Animal Models and Human Reproduction E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Our knowledge of reproductive biology has increased enormously in recent years on cellular, molecular, and genetic levels, leading to significant breakthroughs that have directly benefitted in vitro fertilization (IVF) and other assisted reproductive technologies (ART) in humans and animal systems.
Animal Models and Human Reproduction presents a comprehensive reference that reflects the latest scientific research being done in human reproductive biology utilizing domestic animal models. Chapters on canine, equine, cow, pig, frog, and mouse models of reproduction reflect frontier research in placental biology, ovarian function and fertility, non-coding RNAs in gametogenesis, oocyte and embryo metabolism, fertilization, cryopreservation, signal transduction pathways, chromatin dynamics, epigenetics, reproductive aging, and inflammation. Chapters on non-human primate models also highlight recent advancements into such issues as human in vitro fertilization (IVF) and assisted reproductive technologies (ART).
This book offers animal scientists, reproductive biology scientists, clinicians and practitioners, invaluable insights into a wide range of issues at the forefront of human reproductive health.
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Contents
Cover
Title Page
Copyright
List of Contributors
Chapter 1: Anatomy of the Reproductive System
1.1 Male Genital Organs in Domestic Mammals
1.2 Female Genital Organs in Domestic Mammals
1.3 The Genital System in Domestic Mammals Species by Species
1.4 Genital Organs in Laboratory Mammals
References
Chapter 2: Anatomy of Mammalian (Endocrine) Glands Controlling the Reproduction
2.1 The Hypothalamus Including the Hypophysis
2.2 The Cerebral Epiphysis
2.3 The Thyroid Gland
2.4 The Adrenal Glands
2.5 The Sexual Glands
2.6 The Liver
References
Chapter 3: Models for Investigating Placental Biology
3.1 Introduction
3.2 Classification of Placenta
3.3 Development of Human Placenta
3.4 Modeling Placental Development and Diseases of Placental Origin
3.5 Summary
References
Chapter 4: Early Developmental Programming of the Ovarian Reserve, Ovarian Function, and Fertility
4.1 Introduction
4.2 Impact of Prenatal Environmental Challenges on Fetal Oogonia (Germ Cells)
4.3 Impact of Prenatal Environmental Challenges on Fetal Follicle/Oocyte Numbers (Healthy versus Atretic) and Oocyte Quality
4.4 Impact of Prenatal Environmental Challenges on the Ovarian Reserve (Total Number of Morphologically Healthy Follicles/Oocytes in Ovaries) in Offspring
4.5 Impact of Prenatal Environmental Challenges on Ovarian Function (e.g., Pituitary Gonadotropin Secretion, Ovarian Hormone/Growth Factor Production, Response to Gonadotropins, Follicle Development, Irregular Reproductive Cycles, and Ovulation Rate) in Offspring
4.6 Impact of Prenatal Environmental Challenges on Fertility (as Measured by Conception Rates, Fecundity, or Age at Puberty or Menopause) in Offspring
4.7 Summary and Conclusion
References
Chapter 5: Small Non-Coding RNAS in Gametogenesis
5.1 Small Non-Coding RNAs
5.2 Function of sncRNAs in Gametogenesis
Acknowledgment
References
Chapter 6: The Ovarian Follicle of Cows as a Model for Human
6.1 Introduction
6.2 A Similar Physiology of Folliculogenesis
6.3 Assisted Reproduction
6.4 Testing the Competence Hypothesis
6.5 Conclusion
References
Chapter 7: Production of Energy and Determination of Competence: Past Knowledge, Present Research, and Future Opportunities in Oocyte and Embryo Metabolism
7.1 Introduction
7.2 Measuring Metabolism
7.3 The Relationship Between Oocyte Metabolism and Quality
7.4 Embryo Metabolism
7.5 Metabolic Biomarkers
7.6 Toward Personalized Culture Media: Formulating Media for Specific Maternal Conditions
7.7 Summary
References
Chapter 8: Signal Transduction Pathways in Oocyte Maturation
8.1 Introduction
8.2 Phosphodiesterase
8.3 Gap Junction Communications
8.4 Metabolic Switch (AMPK)
8.5 Conclusion
References
Chapter 9: Pig Models of Reproduction
9.1 Introduction
9.2 Early Embryonic Development
9.3 Oocyte Maturation
9.4 Fertilization
9.5 Tubouterine Contractility
9.6 Development to the Blastocyst Stage
9.7 Pregnancy and Developmental Programming
9.8 Puberty
9.9 Reproductive Disease
9.10 Summary
Acknowledgments
References
Chapter 10: The Mare as an Animal Model for Reproductive Aging in the Woman
10.1 Introduction
10.2 Ovarian Activity and Reproductive Cycles
10.3 The Follicle
10.4 Fertility
10.5 The Oocyte
10.6 Conclusions
References
Chapter 11: Spotlight on Reproduction in Domestic Dogs as a Model for Human Reproduction
11.1 Introduction
11.2 Dog Reproduction
11.3 Dog-Assisted Reproductive Technology
11.4 Dog Contraception
11.5 The Dog as a Model for Human Reproduction
11.6 Concluding Statements
Acknowledgments
References
Chapter 12: Animal Models of Inflammation During Pregnancy
12.1 Introduction
12.2 Local Inflammation of the Pregnant Female Reproductive Tract
12.3 Systemic Inflammation During Pregnancy
12.4 Genetic Models and Cellular Manipulation to Study Inflammation During Pregnancy
12.5 Inflammation During Pregnancy and Offspring Disease
12.6 Perspectives and Conclusions
Acknowledgments
References
Chapter 13: Practical Approaches, Achievements, and Perspectives in the Study on Signal Transduction in Oocyte Maturation and Fertilization: Focusing on the African Clawed Frog Xenopus laevis as an Animal Model
13.1 Introduction to Reproductive Biology of Frog Oocytes and Eggs
13.2 Practical Approaches
13.3 Achievements and Perspectives
Acknowledgments
Appendix
References
Chapter 14: Prezygotic Chromosomal Examination of Mouse Spermatozoa
14.1 Introduction
14.2 Procedure of Sperm Chromosome Screening
14.3 Practical Use of SCS Before Fertilization
14.4 Conclusion
Acknowledgments
References
Chapter 15: Molecular and Cellular Aspects of Mammalian Sperm Acrosomal Exocytosis
15.1 Introduction
15.2 Structure of the Acrosome
15.3 Intermediate Stages of Exocytosis
15.4 Sperm Capacitation Prepare the Sperm to Undergo Acrosomal Exocytosis
15.5 Physiological Site for the Occurrence of Acrosomal Exocytosis
15.6 SNARES and Other Proteins from the Fusion Machinery
15.7 Hyperpolarization
15.8 Actin Cytoskeleton
15.9 Calcium
References
Chapter 16: Sperm Chromatin Dynamics Associated with Male Fertility in Mammals
16.1 Introduction
16.2 Sperm Chromatin Structure Modulates Sperm Nuclear Shape and Function
16.3 The Bull Is a Suitable Model for the Study of Male Fertility in Humans
16.4 Conclusions and Prospects
Acknowledgments
References
Chapter 17: Epigenome Modification and Ubiquitin-Dependent Proteolysis During Pronuclear Development of the Mammalian Zygote: Animal Models to Study Pronuclear Development
17.1 Introduction
17.2 Milestones of Pronuclear Development
17.3 Nuclear Envelope, Nuclear Pore Complexes, and Nuclear Lamina Changes During Pronuclear Development
17.4 Molecular Mechanism of Paternal and Maternal Pronucleus Biogenesis
17.5 Role of UPS in Pronuclear Biogenesis
17.6 Posttranslational Modifications of Pronuclear Histones
17.7 Sirtuin Family Histone Deacetylases in Gametogenesis and Development
17.8 Clinical and Technological Considerations
17.9 Conclusions
Acknowledgments
References
Chapter 18: Alterations of the Epigenome Induced by the Environment in Reproduction
18.1 Introduction
18.2 Epigenetic Reprogramming
18.3 Environment and Epigenetic Alterations
18.4 Animal Models Used in Reproduction to Research Epigenetic Alterations Induced by the Environment
18.5 Effects of Environment on Epigenetic Modifications in Humans
18.6 Epigenetics and Assisted Reproductive Technology (ART)
18.7 Priorities for the Future
Acknowledgments
References
Chapter 19: Toward Development of Pluripotent Porcine Stem Cells by Road Mapping Early Embryonic Development
19.1 Introduction
19.2 Current Status on the Pluripotent State in the Pig Embryo
19.3 Current Status of the Establishment of Porcine Embryonic Stem Cells (pESCs)
19.4 Current Status in Establishment of Porcine-Induced Pluripotent Stem Cells
19.5 Future Perspectives: Use of Global Profiling on Pluripotent Cells from Pig Embryo and Pluripotent Stem Cells
19.6 Discussion and Conclusions
Acknowledgments
References
Chapter 20: Applications of Metabolomics in Reproductive Biology
20.1 Introduction
20.2 Metabolomics and Reproductive Biology
20.3 Metabolomics Studies in Large Animals as Models for Humans
20.4 Conclusions and Future Prospects
Acknowledgments
Conflict of Interest
References
Chapter 21: Cryopreservation of Mammalian Oocytes
21.1 Principles of Cryopreservation
21.2 Cryopreservation of Mammalian Oocytes
Acknowledgments
Abbreviations
References
Index
End User License Agreement
List of Tables
Table 3.1
Table 4.1
Table 4.2
Table 6.1
Table 8.1
Table 9.1
Table 9.2
Table 9.3
Table 9.4
Table 11.1
Table 11.2
Table 11.3
Table 11.4
Table 11.5
Table 11.6
Table 11.7
Table 12.1
Table 12.2
Table 12.3
Table 14.1
Table 19.1
Table 19.2
Table 19.3
Table 19.4
Table 19.5
Table 19.6
Table 20.1
Table 21.1
Table 21.2
List of Illustrations
Figure 1.1
Figure 1.2
Figure 1.3
Figure 1.4
Figure 1.5
Figure 1.6
Figure 1.7
Figure 1.8
Figure 1.9
Figure 1.10
Figure 1.11
Figure 1.12
Figure 1.13
Figure 1.14
Figure 1.15
Figure 1.16
Figure 1.17
Figure 1.18
Figure 1.19
Figure 1.20
Figure 1.21
Figure 1.22
Figure 1.23
Figure 1.24
Figure 1.25
Figure 1.26
Figure 1.27
Figure 1.28
Figure 1.29
Figure 1.30
Figure 1.31
Figure 1.32
Figure 1.33
Figure 1.34
Figure 1.35
Figure 1.36
Figure 1.37
Figure 1.38
Figure 1.39
Figure 1.40
Figure 1.41
Figure 1.42
Figure 1.43
Figure 1.44
Figure 1.45
Figure 1.46
Figure 1.47
Figure 1.48
Figure 1.49
Figure 1.50
Figure 1.51
Figure 1.52
Figure 1.53
Figure 1.54
Figure 1.55
Figure 1.56
Figure 1.57
Figure 1.58
Figure 1.59
Figure 1.60
Figure 1.61
Figure 1.62
Figure 1.63
Figure 1.64
Figure 1.65
Figure 1.66
Figure 1.67
Figure 1.68
Figure 1.69
Figure 1.70
Figure 1.71
Figure 1.72
Figure 1.73
Figure 1.74
Figure 1.75
Figure 2.1
Figure 2.2
Figure 2.3
Figure 2.4
Figure 3.1
Figure 3.2
Figure 3.3
Figure 3.4
Figure 5.1
Figure 5.2
Figure 5.3
Figure 5.4
Figure 6.1
Figure 7.1
Figure 8.1
Figure 8.2
Figure 8.3
Figure 8.4
Figure 8.5
Figure 11.1
Figure 11.2
Figure 11.3
Figure 11.4
Figure 11.5
Figure 11.6
Figure 11.7
Figure 11.8
Figure 11.9
Figure 11.10
Figure 11.11
Figure 11.12
Figure 11.13
Figure 11.14
Figure 11.15
Figure 11.16
Figure 11.17
Figure 11.18
Figure 11.19
Figure 11.20
Figure 11.21
Figure 11.22
Figure 11.23
Figure 11.24
Figure 11.25
Figure 11.26
Figure 11.27
Figure 11.28
Figure 11.29
Figure 11.30
Figure 11.31
Figure 11.32
Figure 11.33
Figure 11.34
Figure 12.1
Figure 12.2
Figure 13.1
Figure 13.2
Figure 14.1
Figure 14.2
Figure 14.3
Figure 14.4
Figure 14.5
Figure 15.1
Figure 15.2
Figure 15.3
Figure 17.1
Figure 17.2
Figure 18.1
Figure 18.2
Figure 18.3
Figure 18.4
Figure 19.1
Figure 21.1
Figure 21.2
Figure 21.3
Figure 21.4
Figure 21.5
Figure 21.6
Figure 21.7
Figure 21.8
Guide
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Table of Contents
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Animal Models and Human Reproduction
Edited by
Heide SchattenDepartment of Veterinary PathobiologyUniversity of Missouri-Columbia, Columbia, USA
and
Gheorghe M. ConstantinescuDepartment of Biomedical SciencesCollege of Veterinary MedicineUniversity of Missouri-Columbia, Columbia, USA
Copyright © 2017 by John Wiley & Sons, Inc. All rights reserved 2017
Published by John Wiley & Sons, Inc., Hoboken, New JerseyPublished simultaneously in Canada
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission.
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Library of Congress Cataloging-in-Publication Data:
Names: Schatten, Heide, editor. | Constantinescu, Gheorghe M., 1932- editor.
Title: Animal models and human reproduction / edited by Heide Schatten, Gheorghe M. Constantinescu.
Description: Hoboken, New Jersey : John Wiley & Sons Inc., [2017] | Includes bibliographical references and index.
Identifiers: LCCN 2016045187| ISBN 9781118881606 (cloth) | ISBN 9781118881422 (Adobe PDF) | ISBN 9781118881347 (epub)
Subjects: | MESH: Reproduction | Models, Animal | Reproductive Physiological Phenomena | Reproductive Techniques
Classification: LCC QH481 | NLM QH 481 | DDC 571.8/4—dc23LC record available at https://lccn.loc.gov/2016045187
List of Contributors
Muhammad Anzar
Agriculture and Agri-Food Canada
Saskatoon Research and Development Center
Saskatoon, Canada
Annick Bergeron
Centre de Recherche en Biologie de la Reproduction
Département des Sciences Animales
Faculté des sciences de l'agriculture et de l'alimentation
Université Laval
Québec, Canada
Mariano G. Buffone
Instituto de Biología y Medicina Experimental (IBYME)
National Research Council of Argentina (CONICET)
Buenos Aires, Argentina
Elaine M. Carnevale
Equine Reproduction Laboratory
Department of Biomedical Sciences
Colorado State University
CO, USA
Gheorghe M. Constantinescu
Department of Biomedical Sciences
College of Veterinary Medicine
University of Missouri-Columbia
Columbia, USA
Thu Dinh
Department of Animal and Dairy Sciences
Mississippi State University
MS, USA
Sule Dogan
IVF Michigan P.C.
MI, USA
Alex C.O. Evans
School of Agriculture and Food Science
University College Dublin
Dublin, Ireland
Kristine Freude
Faculty of Health and Medical Sciences
Department of Veterinary Clinical and Animal Sciences
University of Copenhagen, Denmark
Zhao-Jia Ge
College of Animal Science and Veterinary Medicine
Qingdao Agricultural University
Qingdao, China
Vanessa Hall
Faculty of Health and Medical Sciences
Department of Veterinary Clinical and Animal Sciences
University of Copenhagen
Denmark
Jason R. Herrick
Colorado Center for Reproductive Medicine
CO, USA
Poul Hyttel
Faculty of Health and Medical Sciences
Department of Veterinary Clinical and Animal Sciences
University of Copenhagen
Denmark
James J. Ireland
Michigan State University
MI, USA
Fermin Jimenez-Krassel
Michigan State University
MI, USA
Abdullah Kaya
Department of Animal Reproduction and Artificial Insemination
Selcuk University
Konya, Turkey
Daulat Raheem Khan
Centre de Recherche en Biologie de la Reproduction
Département des Sciences Animales
Faculté des sciences de l'agriculture et de l'alimentation
Université Laval
Québec, Canada
Dario Krapf
Institute of Molecular and Cell Biology of Rosario (CONICET-UNR) and Área Biología
Facultad de Ciencias Biológicas y Farmacéuticas
UNR
Rosario, Argentina
Rebecca L. Krisher
Colorado Center for Reproductive Medicine
CO, USA
Naseer A. Kutchy
Department of Animal and Dairy Sciences
Mississippi State University
MS, USA
Keith E. Latham
Department of Animal Science
Reproductive and Developmental Science Program
Michigan State University
MI, USA
Kaveh Mashayekhi
Faculty of Health and Medical Sciences
Department of Veterinary Clinical and Animal Sciences
University of Copenhagen
Denmark
and
BioTalentum Ltd.
Aulich Lajos str. 26. 2100
Gödöllő, Hungary
and
Sandor Life Sciences
Sandor Medicaids Group Pvt. Ltd.
Hyderabad, 500043 India
Erdogan Memili
Department of Animal and Dairy Sciences
Mississippi State University
MS, USA
B.R. Mordhorst
Division of Animal Science
University of Missouri-Columbia
Columbia, USA
Francesca Mossa
Dipartimento di Medicina Veterinaria
Università degli Studi di Sassari
Sassari, Italy
Arlindo Moura
Department of Animal Sciences
Federal University of Ceara
Fortaleza, Brazil
Jan Nevoral
Department of Veterinary Sciences
Czech University of Life Sciences
Prague, Czech Republic
and
Division of Animal Science
University of Missouri-Columbia
Columbia, USA
Rodrigo Oliveira
Department of Animal Production
Federal Rural University of Rio de Janeiro
Rio de Janeiro, Brazil
D. V. Krishna Pantakani
Department of Clinical Chemistry
University of Göttingen
Göttingen, Germany
Laramie Pence
Animal Bioscience and Biotechnology Laboratory
USDA Agricultural Research Science
MD, USA
and
Department of Animal and Avian Sciences
University of Maryland
MD, USA
Stoyan Petkov
Institute for Farm Animal Genetics
Friedrich-Loeffler-Institute
Neustadt, Germany
R.S. Prather
Division of Animal Science
University of Missouri-Columbia
Columbia, USA
and
National Swine Resource and Research Center
University of Missouri-Columbia
Columbia, USA
Karen E. Racicot
Department of Obstetrics
Gynecology and Reproductive Biology
Reproductive and Development Science Program
Van Andel Institute
Michigan State University
MI, USA
François J. Richard
Centre de Recherche en Biologie de la Reproduction
Département des Sciences Animales
Faculté des sciences de l'agriculture et de l'alimentation
Université Laval
Québec, Canada
Nicolas Santiquet
National Foundation for Fertility Research
Lone Tree
CO, USA
Ken-ichi Sato
Laboratory of Cell Signaling and Development
Department of Molecular Biosciences
Faculty of Life Sciences
Kyoto Sangyo University
Kyoto, Japan
Heide Schatten
Department of Veterinary Pathobiology
University of Missouri-Columbia
Columbia, USA
Elena Silva
Colorado Center for Reproductive Medicine
CO, USA
Marc-André Sirard
Département des Sciences Animales Pavillon des services
Chaire de Recherche du Canada en Génomique Animale, Canada
Lukasz Smorag
Institute of Human Genetics
University of Göttingen
Göttingen, Germany
Florenza A. La Spina
Instituto de Biología y Medicina Experimental (IBYME)
National Research Council of Argentina (CONICET)
Buenos Aires, Argentina
Cintia Stival
Institute of Molecular and Cell Biology of Rosario (CONICET-UNR) and Área Biología
Facultad de Ciencias Biológicas y Farmacéuticas
UNR
Rosario, Argentina
Peter Sutovsky
Division of Animal Science
University of Missouri-Columbia
Columbia, USA
and
Department of Obstetrics
Gynecology and Women's Health
University of Missouri-Columbia
Columbia, USA
Hiroyuki Tateno
Department of Biological Sciences
Asahikawa Medical University
Asahikawa, Japan
Bhanu P. Telugu
Animal Bioscience and Biotechnology Laboratory USDA Agricultural Research ScienceMD, USA
and
Department of Animal and Avian Sciences
University of Maryland
MD, USA
Ana Luiza Cazaux Velho
Department of Animal and Dairy Sciences
Mississippi State University
MS, USA
and
Department of Animal Science
Federal University of Ceara
Fortaleza, Brazil
Siobhàn W. Walsh
Department of Chemical and Life Sciences
Waterford Institute of Technology
Waterford, Ireland
Hiroyuki Watanabe
Department of Biological Sciences
Asahikawa Medical University
Asahikawa, Japan
Shirley J. Wright
Department of Biology
University of Dayton
OH, USA
Shen Yin
Key Laboratory of Animal Reproduction and Germplasm Enhancement in Universities of Shandong
College of Animal Science and Technology
Institute of Reproductive Sciences
Qingdao Agricultural University
Qingdao, China
1Anatomy of the Reproductive System
Gheorghe M. Constantinescu
Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri-Columbia, Columbia, USA
The complexity of the organs that the mammalian reproductive system consists of, necessitates a general view of the systematization and short description of each structure involved. The following domestic mammals are subject of this chapter: cat (Felis catus), dog (Canis familiaris), pig (Sus scrofa domestica), large ruminant (Bos Taurus), sheep (Ovis aries), goat (Capra hircus), and horse (Equus caballus).
The anatomy of the reproductive system of laboratory animals and the nonmammalian animal models follow the description of domestic mammals' anatomy (König and Liebich, 2004; Nickel et al., 1984). The laboratory animals are the rabbit (Oryctolagus cuniculus), the mouse (Mus musculus), and the rat (Rattus norvegicus). The nonmammalian animal models are the African clawed frog (Xenopus laevis L.) and the zebrafish (Brachidanio/Danio rerio).
The English anatomical terms are translated from Nomina Anatomica Veterinaria (NAV) (2012, op. cit. as ICVGAN) and from Gheorghe M. Constantinescu and Oskar Schaller, Illustrated Veterinary Anatomical Nomenclature 4th edn, Thieme (2012, op. cit.). For the corresponding terms in humans, the following reference is suggested: Heinz Feneis and Wolfgang Dauber, Pocket Atlas of Human Anatomy Based on the International Nomenclature (2000, op. cit.).
1.1 Male Genital Organs in Domestic Mammals
The male reproductive system of all mammalian species, including the laboratory animals, consists of the paired testicle, epididymis, ductus deferens, spermatic cord, accompanying tunics, accessory genital glands (single structures or pairs), the male urethra, the penis, and the prepuce.
Details of all components of the male reproductive system can be found in Schatten and Constantinescu (2007), Blackwell (op. cit.), Constantinescu and Constantinescu (2010), Omphaloskepsis (op. cit.), deLahunta and Habel (1986), Saunders (op. cit.), and Dyce (2010), 4th edn, Elsevier (op. cit.). For the laboratory animals except the rabbit, the details can be found in Constantinescu (2011) (a Color (water color) Atlas and Text, AALAS (op. cit.)). For the rabbit the details can be found in Barone (1973) Masson (op. cit.), and Barone (1978) École Nationale Vétérinaire Lyon (op. cit.).
1.1.1 The Testicle
The male gonad, with endocrine and exocrine functions, the testicle, is the essential organ of the male reproductive system, producing testosterone and spermatozoa, respectively. It has an ovoid shape, with the long axis species-specific oriented, a lateral and a medial surfaces, a free and an epididymal border, a head end, where the head of the epididymis is attached, and a tail end, where the tail of the epididymis is attached. (The body of the epididymis is not attached to the testicle.)
The testicle is intimately covered by a white and inextensible fibrous capsule called Tunica albuginea, which runs inside of the testicle walls, called Septa or Septula, which separate the testicular tissue into lobes (see Figure 1.1). Within the lobes, the testicular parenchyma, which is the functional tissue of the testis, consists of seminiferous tubules, Leydig cells, and Sertoli cells. The seminiferous tubules start as convoluted, and end as straight tubules that build up the rete testis within the mediastinum testis. The septa/septula converge into a structure called mediastinum testis.
Figure 1.1 Internal organization of testicle and epididymis.
1.1.2 The Epididymis, Ductus Deferens, and Spermatic Cord
The epididymis is the first excretory organ of the male reproductive system. It presents a head, a body, and a tail, all surrounded by the continuation of the testicular albuginea. The epididymis consists of ductuli efferentes—the continuation of the rete testis, and the ductus epididymidis.
The ductus deferens is the continuation of the ductus epididymidis and opens on the roof of the prostatic urethra at the level of colliculus seminalis. Within the spermatic cord it is connected to the mesorchium by the mesoductus deferens, whereas within the peritoneal cavity it is connected with the symmetrical duct and the paired ureter by the genital fold. An embryonic remnant of the fetal uterus (uterus masculinus) can be seen in some species within the genital fold.
The spermatic cord (Funiculus spermaticus) (see Figure 1.2) consists of the following:
The ductus deferens with its blood and nerve supply surrounded and attached to the
mesorchium
by the
mesoductus deferens
The blood and lymphatic vessels and nerves supplying the testicle and the epididymis and smooth muscle fibers, all surrounded by the
visceral lamina of the vaginal tunic
and collectively called mesorchium.
Figure 1.2 Transverse section through the spermatic cord (outlined by the broken line).
The spermatic cord is connected to the parietal lamina of the vaginal tunic by the mesofuniculus.
1.1.3 The Descent of the Testicle
Starting its development on the roof of the abdominal cavity, the testicle with the epididymis is connected to the skin by a long mesenchymal tract (ligament) called gubernaculum testis, which runs within the inguinal canal. (The inguinal canal is outlined by the superficial and deep inguinal rings, the arcus inguinalis, and the internal abdominal oblique M. For details, see any veterinary anatomy book.) Pushing the transverse fascia and the parietal peritoneum through the deep inguinal ring, it will appear lined by the peritoneum under the name of vaginal ring. The space between the parietal and the visceral laminae of the vaginal tunic (continuation of peritoneum) within the inguinal canal is called vaginal canal, and that surrounding the testicle is called vaginal cavity. Before the testicle passes through the inguinal canal surrounded by the intraabdominal tunics (see below), these tunics enclosing the gubernaculum testis protrude through the inguinal canal under the embryological term of vaginal process. By the retraction of gubernaculum testis, the testicle passes through the inguinal canal and establishes finally within the scrotum (see below). After birth, the gubernaculum testis is represented by three ligaments: proper ligament of testicle (between the tail head of the testicle and the tail of the epididymis), the ligament of the tail of the epididymis (between the tail of epididymis and the external spermatic fascia), and the scrotal ligament (between the external spermatic fascia and dartos).
1.1.4 The Tunics of the Spermatic Cord and the Testicle
The systematization of these tunics in intraabdominal and extraabdominal eases their comprehension.
1.1.4.1 The Intraabdominal Tunics
These are the structures that are brought by the testicle from the abdominal cavity during its descent. The internal spermatic fascia is the continuation of the transverse fascia. The vaginal tunic is the continuation of the peritoneum (see above). The cremaster M. protected by the cremasteric fascia is intimately attached to the internal spermatic fascia, as a bundle of fibers from the internal abdominal oblique M.
1.1.4.2 The Extraabdominal Tunics
These are structures outside of the inguinal canal. They consist of the external spermatic fascia, which continues the superficial fascia of the abdomen and the loose subcutaneous connective tissue, and the skin which in the testicular area duplicates in a skin layer, the scrotal skin, and a layer of smooth muscle fibers called Tunica dartos. Together the scrotal skin and the tunica dartos are called Scrotum. The symmetrical external spermatic fascia surrounds the penis as the superficial fascia of penis, and continues in the perineal region as the deep perineal fascia. Tunica dartos surrounds the penis as the deep fascia of penis and continues as the superficial perineal fascia.
1.1.5 The Accessory Genital Glands
The glands of the ampullae of the ductus deferens, the vesicular glands/seminal vesicles, the prostate, and the bulbourethral glands differ from species to species in number and aspect, and from intact male to a sexually immature or an orchiectomized male.
There are no ampullae of the ductus deferens in the cat and in the pig. The vesicular glands are present in ungulates, but in the horse they are called seminal vesicles. The carnivores lack the vesicular glands. The prostate is the only accessory gland in the dog. In all species it consists of a body (surrounding the prostatic urethra) and a disseminate part (within the walls of the urethra). The latter is found in the pig, ox, and goat, is deficient ventrally in the sheep, and represented by a few lobules in carnivores. No disseminate part of prostate is found in the horse. The bulbourethral glands, absent only in the dog, are located symmetrically at the level of the curvature made by the urethral isthmus, between the pelvic and the penile parts of urethra.
1.1.6 The Penis and the Prepuce
The penis is an external genital, and the male organ of copulation. It consists of a root, a body, and a free part surrounded and protected by the prepuce, and the glans penis.
The root of the penis consists of two crura and the bulbus penis. The paired crus penis is the origin (proximal end) of corpus cavernosum penis. They are attached to the ischiatic arch covered by the ischiocavernosus muscles and join with each other in a “V”-shaped fashion to build up the corpus cavernosum penis. Between the two crura the bulbus penis is located. The latter is a proximal enlargement (at the origin) of spongy tissue that surrounds the penile urethra, spongy tissue called corpus spongiosum penis.
The body of the penis is represented by the continuation of the two crura, distally, and is called corpus cavernosum penis. The penile urethra surrounded by the corpus spongiosum penis runs on the ventral side of it.
The free part of the penis includes the glans penis, distal to the attachment of the prepuce. The glans penis is the head of the penis, containing the corpus spongiosum glandis. In the tomcat a cartilage, and in the dog, mouse, and rat an os penis is included. Species-specific characteristics will be detailed later on.
The prepuce is the skin surrounding and protecting the free part of the penis in the resting position. It is a fold of skin consisting of an external and an internal laminae, continuous at the preputial ostium. The internal lamina attaches to the origin (proximal end, or base) of the free part of the penis, where it continues with the skin of the free part of the penis, visible when the penis is fully erect.
1.2 Female Genital Organs in Domestic Mammals
The female reproductive system of all mammalian species consists of the paired ovary, uterine, or fallopian tube (salpinx), and the uterus, the vagina, the vestibule, vulva, and clitoris. The mammary glands are associated with the female genital organs, and will be described in general terms.
Details of all components of the female reproductive system can be found in Schatten and Constantinescu (2007, op. cit.)
1.2.1 The Ovary
Similar to the male, the female gonad is a mixed gland with endocrine and exocrine functions. The ovary is the essential organ of the female genital system, producing progesterone, and estradiol, also oxytocin, relaxin, inhibin, and activin. As the exocrine function the ovary produces ovules (ovocytes, oocytes). Ovoid in shape, with a medial and a lateral surface, a free and mesovarian borders, tubal and uterine extremities, the ovary is provided with a hilus.
Notice that the mesovarium is attached to the mesovarian border, opposite to the free border, and the uterine extremity (toward the tip of the uterine horn) is opposite to the tubal extremity, in close proximity to the infundibulum of the uterine tube. Also, the hilus is the area of attachment of the mesovarium, and entrance of ovarian vessels.
A tunica albuginea intimately covers the ovary, similar to that of the testicle. In all species the stroma is the framework of the ovary (see Figures 1.3 and 1.4), consisting of fibrous tissue and smooth muscle, whereas the parenchyma is the functional tissue of the ovary. Except in the horse, the ovary consists of a peripheral cortex and a central medulla. In the mare the cortex is central, and the medulla is peripheral.
Figure 1.3 Internal organization of the mare's ovary.
Figure 1.4 Internal organization of the cow's ovary.
The cortex of the most mammals except the mare, which is also called the parenchymal zone, contains all categories of follicles: primary, secondary, tertiary (vesicular ovarian follicles), the corpus luteum, the corpus albicans, and atretic ovarian follicles. A mature follicle eliberates the ovule, which leaves the ovary through the cortex.
The medulla, also called the vascular zone, consists of vessels and nerves nourishing the ovary and is located in all species except the mare, after entering the hilus. In the mare, the free border of the ovary has an indentation/depression called the ovarian fossa, where the mature ovule leaves the ovary (the ovulation occurs), reason that some clinician call the ovarian fossa ovulation fossa.
The ovary is connected to the surrounding structures by the suspensory ligament (to the diaphragm), the proper ligament (to the apex of the uterine horn), and the mesovarium (which is the most cranial segment of the broad ligament). In a similar manner in which the mesepididymis separates the mesorchium in a proximal and a distal segment, the mesosalpinx separates the mesovarium into a proximal and distal segment.
Two groups of vestigial structures from the developmental life called epoöphoron and paroöphoron may be associated with the ovary after birth.
1.2.2 The Uterine Tube: Salpinx, Fallopian Tube
The uterine tube extends from the apex of the uterine horn (where it is attached to), and this is called the uterine end, to the vicinity of the ovary (and this is called the ovarian end) on the lateral side of the broad ligament. It is flexuous and has an uneven size, basically being divided into two distinct portions, the ampulla and the isthmus. We can distinguish two openings or ostia, the infundibulum, and the fimbriae, and in some species (carnivores, horse) the uterine part of the uterine tube, provided with a papilla.
The closest opening to the ovary is the abdominal ostium within the infundibulum. The latter is the funnel-shaped ovarian end of the tube. The infundibulum is provided with a fringe of processes called fimbriae, around the opening of the infundibulum. The fimbria, which is intimately attached to the ovary, is called ovarian fimbria. It is important to mention that the abdominal opening of the uterine tube corresponds to the peritoneal cavity, allowing the connection between the external environment (through the vagina) and the peritoneal cavity. The ampulla is the widest part of the tube, between the abdominal ostium and the isthmus. The isthmus is the narrow part of the salpinx, continuing with the uterine part of the tube. The uterine part of the salpinx is the shortest segment of the tube. It passes through the wall of the apex of the uterine horn and in some species (see above) ends on a papilla, whereas in the other species the salpinx gradually continues with the uterine horn. At this level, the salpinx opens into the uterus through the uterine ostium of the uterine tube.
As a part of the broad ligament, the mesosalpinx holds in place the uterine tube. The ovarian bursa is outlined by the distal mesovarium, the mesosalpinx, and the ovary. The entrance into the ovarian bursa is medially oriented.
1.2.3 The Uterus
The uterus is the organ of pregnancy, or gestation. In most mammals it consists of three major components: two horns, one body, and one cervix or neck, and it is called uterus bicornis. In the rabbit and the rat, the horns and cervix are paired, this type of uterus being called uterus duplex. In these two species the uterine horns run together side by side for a short distance caudally, and end by their own cervices. Therefore, there is no body of uterus in these two species. In primates, including humans, the uterus has only one body and the cervix, which is a characteristic of the uterus simplex. Nevertheless, Feneis and Dauber (2000) 5th edn Thieme (op. cit.) listed on p. 168.9 right and left uterine horns as “pointed extensions of the uterus at the entrance of the uterine tubes owing to the incomplete union of both paramesonephric ducts” (from the intrauterine development).
The uterine horns of the uterus bicornis and duplex expose mesometrial and free borders, and corresponding cavities. The uterine body and the cervix of the uterus bicornis have a right and a left mesometrial border, a dorsal and a ventral surface, and a cavity (for the cervix the cavity is called cervical canal). The cervices of the uterus duplex expose short right and left mesometrial borders, dorsal and ventral surfaces, and their own, totally separated from each other, cervical canals. In all species the cervix has two openings: the internal uterine orifice opening toward the uterus and an external uterine orifice, between the cervix and the vagina.
The uterine horns vary from species to species in shape, size, and location. Each uterine horn has two openings: at the apex (tip) it communicates with the uterine tube through the uterine orifice of the tube, whereas caudally it opens into the body of the uterus. Here they are separated by a fold of mucosa called uterine velum, except in the mare. The mesometrial borders serve for the attachment of the mesometrium, the last component of the broad ligament.
The body of uterus is a unique compartment, where the embryo and the fetus develop before birth. In the mare, because of the lack of uterine velum, the caudal extent of the uterine body is called fundus. The mesometrium is provided with the round ligament of the uterus, which may extend from the apex of the uterine horn or uterine body to the deep inguinal ring enclosed in a lateral fold of the broad ligament. The round ligament of the uterus in carnivores will be described later.
The cervix has thick muscular walls and a narrow canal through which the fetus will exit the uterus. It has different species-specific structures, which make easy or complicate the birth and the artificial insemination (A.I.). It is important to note that the cervix has two distinct parts: a prevaginal and a vaginal part. The former is the part of the cervix cranial to the vagina, and the latter is the part that protrudes into the vagina. The more the cervix projects into the vagina, the deeper the vaginal fornix, the cranial blind pouch of the vagina surrounding the vaginal part of the cervix. Both vaginal part of the cervix and the fornix are very important structures in the mare and the female dog.
1.2.4 The Vagina and the Vestibule
The vagina is the canal located between the cervix and the external urethral orifice, or the hymen. The vaginal fornix has already been described. The hymen is a poorly developed transverse fold of the floor of the vagina just cranial to the external urethral ostium. The vagina opens into the vestibule through the vaginal ostium. Remnants of embryological structures can be seen on the floor of the vagina, on both sides of the external urethral orifice in the cow.
The last compartment of the female genital organs, the vestibule, communicates cranially with the vagina and caudally with one of the external parts of the female genital organ, the vulva. It is a very long canal in the domestic mammals in comparison to humans, and with the exception of the cat, shorter than the vagina. In the domestic mammals it is not considered an external organ, as it is considered in humans. On the lateral walls and the floor of the vestibule, an erectile tissue (the vestibular bulb) and several glands can be seen. The constrictor muscle of the vestibule and vagina is well developed in the female dog and the mare. A suburethral diverticulum is shown in the sow and the ruminants. In the female dog a urethral tubercle is seen at the vastibulovaginal junction.
1.2.5 The Vulva and the Clitoris
In the domestic mammals the vulva and the clitoris are considered the female external genital parts.
The vulva is located in a subanal position and is provided by two pairs of labia, major and minor, not easily distinguishable in the domestic mammals, as in humans, with some exceptions. Usually the vulva consists of two symmetrical labiae. The labiae meet in a dorsal and a ventral commissures, differently shaped in the domestic mammals. The contact borders of the two labiae between the two commissures outline the pudendal fissure, the external urogenital opening.
Rudimentary partial homologue of the penis, the clitoris is located on the floor of the vestibule (some exceptions in laboratory animals). The only notable difference between the penis and the clitoris consists of the lack of urethra in the clitoris. The two crura and the body with the corpus cavernosum, the glans with the corpus spongiosum, and the fascia of the clitoris are the major components of this organ. The glans is protected within the fossa of the clitoris. The prepuce and the frenulum are also associated with the clitoris.
1.2.6 The Mammary Gland
The mammary gland(s) are associated with the female genital system. A detailed description for all species of domestic mammals with the blood supply, lymph drainage, and nerve supply is available in Schatten and Constantinescu (2007, op. cit.).
1.3 The Genital System in Domestic Mammals Species by Species
The male and the female genital systems in all species will follow the same step-by-step description as it was chosen for the general description, single or several structures under the same section.
In Section 1.3.1.1, the first section describes the testicle, epididymis, ductus deferens, spermatic cord, and investing tunics in the male. The second section describes the accessory genital glands, the third section describes the penis and the prepuce, and the fourth section describes the male urethra.
Section 1.3.1.2 consists of five sections providing a general description on female reproductive organs. No mammary glands will be described as a separate section. Illustrations are provided for the domestic mammals in Schatten and Constantinescu (2007, op. cit.), and for the laboratory animals (see Figures 1.68–1.70).
1.3.1 The Genital System in the Carnivores: Cat and Dog (Constantinescu, 2002)
1.3.1.1 Male Genitalia
The Testicle, Epididymis, Ductus Deferens, Spermatic Cord, Tunics
The descent of the testicles occurs very late during the development (around the second week after birth). They reach the scrotum at the end of the third week.
The testicles are located just under the anus in the cat, and in the lower perineal region in the dog (between the two thighs). Globular in shape, the testicles of the cats and dogs are oblique, with the long axis cranioventrally oriented. The testicular artery running deep to the albuginea makes a species-specific characteristic design (see Figures 1.5 and 1.6). The average weight of testicles in the cat is 1.3 g, whereas in the dog it varies with the breeds between 7 and 20 g.
Figure 1.5 Testicle of the dog: lateral aspect.
Figure 1.6 Testicle of the dog: medial aspect.
The epididymis is similar in cats and dogs, and it follows the general description. The ductus epididymidis is as long as 1.5–3 mm in the cat, and 5–8 mm in the dog.
The ductus deferens lack the ampulla in the cat, and in the dog is less distinct. Since there are no vesicular glands in both species, there is no ejaculatory duct.
The spermatic cord is the longest in the cat, because of the location of the testicles, and runs horizontally. In the dog it is slightly obliquely oriented in a dorsocranial direction.
The testicular tunics are similar to the general description, but the characteristic for both species is the fact that there is no ligament of the tail of the epididymis. The parietal lamina of the vaginal tunic and the internal spermatic fascia are adherent to the tail of the epididymis, which does not leave any space for the ligament of the tail of the epididymis. Instead, the scrotal ligament connects the tail of the epididymis directly to the tunica dartos.
Accessory Genital Glands
No ampullae of the ductus deferentes, no vesicular glands are present in both species.
The prostate (see Figure 1.7) is common to both species. In the cat the body of the prostate is bilobed, with a slightly lobulated surface, and does not completely surround the urethra, leaving ventrally a free space. The disseminate part is limited to the dorsal wall of the intrapelvic urethra. In the dog the body of the prostate is voluminous, bilobed, with a lobulated surface, and surrounds the urethra completely. The disseminate part is located similar to that of the cat.
Figure 1.7 Accessory genital glands in the male dog: dorsal view.
The bulbourethral glands are present in the cat only. They are located dorsolateral to the urethral isthmus, spheroidal in shape, and pretty voluminous (5–6 mm in diameter).
The Penis and the Prepuce
The main characteristic of the carnivores penis is the fact that a cartilage in the cat, and a bone in the dog (Os penis) are found within the glans penis. The cartilage of the cat may ossify. The os penis of the dog is triangularly shaped on a transverse section and presents a ventral groove that protects the urethra and the corpus spiongiosum glandis.
In the cat the location of the penis is just ventral to the testicles, and obliquely oriented in a ventrocaudal direction, with the urethral aspect in a dorsal position. During the erection it changes to a ventrocranial oblique position, with the urethral side ventral. The penis is provided with more erectile tissues than the penis of the dog. The glans penis is short and conique, and provided with numerous keratinized papillae oriented toward the base of the penis.
In the dog the penis is located in a subabdominal position, parallel to the ventral contour of the abdominal wall. The crura of the corpus cavernosum are long and covered by strong and voluminous ischiocavernosus muscles. They connect with one another in the corpus cavernosum penis, which distinctly shows the separation between the two halves; even though they are fused, a thick septum separates the two halves. The corpus spongiosum penis, which continues with the corpus spongiosum glandis, is poorly developed in comparison to the cat. The former begins with the bulbus penis, which in the dog is paired and covered by the bulbospongiosus muscle. It is big, originates close to the ischial arch, and extends close to the scrotum. The corpus spongiosum glandis surrounds the penile urethra.
The body of the penis is short. Instead, the glans penis is voluminous and long, and consists of a bulb and a long part. The bulbus penis, which covers dorsally the proximal part of the os penis, is 2.5 cm in diameter in the resting functional status, whereas during the copulation it can reach 8 cm in diameter. With the help of the symmetrical constrictor muscle of bulbus vestibuli (of the female), and the slow engorgement of the bulb, the penis is “locked” and allows the male to perform the second time of copulation, which lasts approximately 20 min. For details, see Evans (1993), Saunders (op. cit.), and Evans and deLahunta (2013), Elsevier (op. cit.). The long part of the glans penis surrounds the “V”-shaped part of the os penis. A corona glandis is present in the dog (see Figure 1.8).
Figure 1.8 Penis of the dog.
The prepuce of the cat is detached and placed under the scrotum. It is short and opens in a caudal direction The preputial orifice is directed caudoventrally. In the dog the prepuce is long and in its cranial portion is attached to the ventral wall of the abdomen only by a fold of skin. The internal lamina is attached to the middle of bulbus glandis and covers the rest of the gland as the penis skin. The preputial cavity is wide. A pair of cranial preputial muscles is attached to the prepuce.
The Male Urethra
In the cat the preprostatic part of the pelvic urethra is much longer than that of the dog. In both species the prostatic part is associated with the prostate gland. The urethral crest and the colliculus seminalis are prominent in both species. There are only two symmetrical openings on both sides of colliculus seminalis for the ductus deferentes (no vesicular glands in carnivores). A spongy layer (cavernous tissue) surrounds the pelvic urethra and continues with the corpus spongiosum penis. The urethralis muscle surrounds the pelvic urethra, and continues as the bulbospongiosus muscle, which surrounds the penile urethra and the bulbus penis. The urethra opens distally by the external urethral orifice. The bulboglandularis muscles are present only in the cat.
1.3.1.2 Female Genitalia (see Figure 1.9)
The Ovary
Bean shaped and flat, the ovaries are protected within the ovarian bursae. The entrance into the ovarian bursa of the dog is very narrow. The suspensory ligament is very long, while the proper ligament of the ovary is much shorter.
Figure 1.9 Genital apparatus of the female dog: dorsal aspect.
The Salpinx
Twice as long in the dog as in the cat, the uterine tubes are very narrow and each ends on a small uterine papilla. The flexuosity shown in the large mammals is almost absent.
The Uterus
Twice as long and wide in the dog as in the cat, the uterine horns have rounded cranial ends and they meet with each other to form the body of the uterus caudally.
The uterine body is also twice as long and wide in the dog as in the cat. Inside, it is provided with a uterine velum starting from the junction of the two horns, and which incompletely separates the uterine cavity.
The cervix in carnivores (see Figure 1.10) has unique characteristics, very important during the performing of the A.I. (see McCarthy (2005), p. 414, Elsevier op. cit.). The cervical canal is short, and communicates with the uterine body by the internal uterine orifice. The vaginal part of cervix protrudes into the vagina on the roof as a rounded cervical tubercle, which continues as a very developed dorsal median fold. Thus, the external uterine orifice opens on the ventral aspect of the cervical tubercle, and is directed toward the vaginal floor. The vaginal fornix is located only on the ventral side of the tubercle—the external uterine orifice is not surrounded by the fornix as it is in the large mammals. In the cat the cervical tubercle has fine folds.
Figure 1.10 Sagittal section through the uterus and vagina of the dog. (Modified and redrawn from Evans (1993).)
The broad ligament consists of the mesovarium, mesosalpinx, and mesometrium. The round ligament of the uterus originates from the lateral surface of mesometrium and in the dog it is enclosed in a fold of the broad ligament and passes through the inguinal canal accompanied by the transverse fascia and the parietal peritoneum collectively known as the vaginal process. The round ligament of the uterus concealed within the vaginal process exits the inguinal canal and can be felt under the skin as far as close to the vulva. In the cat the round ligament of the uterus is not accompanied by the vaginal process (see Watson, 2009, op. cit.).
The Vagina and the Vestibule
The vagina is a very long canal in the dog as against that in the cat, and lasts from the external uterine ostium to the external urethral ostium, located on the floor between the vagina and the vestibule. The most important structures of the mucosa are the cervical tubercle and the dorsal median fold. Along with the other smaller longitudinal mucosal folds, the urethral tubercle (in the dog only), and the shallow transversal ridge of the mucosa (the potential hymen) cranial to the external urethral orifice, these are the most relevant structures of the vagina in both species.
The last of the internal genital organs, the vestibule, has a very peculiar position—it is caudoventrally obliquely oriented, which makes the A.I. technique difficult, especially for the beginners. In length the vestibule of the cat is proportionately much longer than that of the dog, and seems to have the same length as the vagina. The external urethral orifice opens in a deep mucosal groove—there is no urethral tubercle. The vestibular bulb, involved in the mating process, is present only in the dog, surrounded by a rich venous plexus. In the cat only the venous plexus persists, richer and denser than in the dog. The minor vestibular glands are present in both species, whereas the major glands are present only in the cat.
The Vulva and the Clitoris
Together with the clitoris, the vulva is a part of the external genital organs. The vulvar labiae are thick in both species, and sometimes the major labiae can be differentiated from the minor labiae, especially in the dog. The dorsal commissure of the vulva is rounded in the dog and pointed in the cat, whereas the ventral commissure is pointed in the dog and rounded in the cat.
Very large in both species especially in the dog, the clitoris consists of two crura (2–3 cm in the dog), a body (4 cm in the dog), and the glans. The crura and the body lie on the floor of the vestibule, whereas the glans (less visible in the cat than in the dog) lies on the floor of the clitoral fossa. The cat clitoral glans includes a small cartilage that resembles the os penis of the male. In the resting position the clitoris of the dog lies in the clitoral fossa with the glans down as shown on page 428, Fig. 13-6 in McCarthy (2005, op. cit.). During copulation, the clitoris becomes erect and takes a considerable role in the process.
1.3.2 The Genital System in the Pig
1.3.2.1 Male Genitalia
The Testicle, Epididymis, Ductus Deferens, Spermatic Cord, and Tunics
In the pig the descent of the testicles occurs several days before birth (around the 110th day of gestation). The cryptorchidism is relatively frequent in this species.
The long and eliptical testicles are very large in the boar. They are located in a subanal position, close to the anus, with the tail ends oriented dorsocaudally. The location of the testicles pulls the spermatic cords far caudally. They are very long, and the inguinal canal is very much obliquely oriented, which causes frequent inguinal herniae. The species-specific design of the testicular artery is shown in Figures 1.11 and 1.12.
Figure 1.11 Testicle, epididymis, and spermatic cord of the boar: lateral aspect.
Figure 1.12 Testicle of the boar: the free border.
The epididymis is voluminous. Its tail is so much detached that it looks like an appendix to the testicle. The epididymal duct is long and tortuous. The proper ligament of the testicle and the ligament of the tail of the epididymis are strong.
The ductus deferens is as long as the spermatic cord. It is not provided with an ampulla. After exiting the vaginal canal it changes the direction in a sharp caudal angle, crosses the direction of the corresponding ureter and ventral to it in its way to the prostatic urethra, covered by the vesicular gland. In castrated males the entire abdominal route of the ductus deferent is exposed. The genital fold binds down the paired ureters, the ductus deferentes, and the cranial extents of the vesicular glands. In the final leg of its journey, the ductus deferens passes through the prostate gland and opens on the corresponding side of the colliculus seminalis.
The spermatic cord is slightly different from the other species in that the mesofuniculus is in a vertical position and attached to the dorsal wall of the vaginal canal.
