1. Introduction and Some Preliminary Considerations 1
•• Basic Qualities of Living Organisms 1
•• Reproduction 1
•• Development of a Human Being 2
•• Embryology 3
•• Subdivisions of Embryology 3
•• Importance of Embryology in the Medical Profession 4
•• Basic Processes in Embryology 4
2. Genetics and Molecular Biology in Embryology 7
•• Genetic Basis of Developmental Anatomy 7
•• Genes 8
•• Chromosomes 11
•• Inheritance of Genetic Disorders 16
•• Cell Division 18
3. Reproductive System, Gametogenesis, Ovarian and Menstrual Cycles 22
•• Male Reproductive System 23
•• Female Reproductive System 25
•• Gametogenesis 27
•• Ovarian Cycle 33
•• Menstrual Cycle 39
•• Hormonal Control of Ovarian and Uterine Cycles 43
4. Fertilization and Formation of Germ Layers 45
•• Fertilization 46
•• Sex Determination 51
•• Test Tube Babies/In Vitro Fertilization 51
•• Cleavage 52
•• Formation of Germ Layers 54
•• Time Table of Events Described in this Chapter 58
•• Embryological Explanation for Clinical Conditions or
Anatomical Observations 59
5. Further Development of Embryonic Disc 61
•• Formation of Notochord 62
•• Formation of the Neural Tube 65
•• Subdivisions of Intraembryonic Mesoderm 65
•• Lateral Plate Mesoderm—Formation of Intraembryonic Coelom 67
•• Intermediate Mesoderm 67
•• Yolk Sac 67
•• Folding of Embryo 67
•• Connecting Stalk 69
•• Allantoic Diverticulum 69
•• Effect of Head and Tail Folds on Positions of Other Structures 71
•• Time Table of Events Described in this Chapter 72
xii Human Embryology
6. Placenta, Fetal Membranes and Twinning 73
•• Formation of Placenta 73
•• Fetal/Extraembryonic Membranes 88
•• Multiple Births and Twinning 93
•• Embryological Basis for Clinical Conditions or
Anatomical Observations 95
7. Formation of Tissues of the Body 98
•• Epithelia 99
•• Connective Tissue 101
•• Muscular Tissue 112
•• Nervous Tissue 114
8. Integumentary System (Skin and Its Appendages, Mammary Gland) 118
•• Skin 118
•• Appendages of Skin 120
•• Time Table of Some Events Described in this Chapter 124
•• Embryological Explanation for Clinical Conditions or
Anatomical Observations in Skin 124
9. Pharyngeal Arches 126
•• Pharyngeal/Branchial Arches 127
•• Derivatives of Skeletal Elements 128
•• Nerves and Muscles of the Arches 129
•• Fate of Ectodermal Clefts 129
•• Fate of Endodermal Pouches 131
•• Development of Palatine Tonsil 132
•• Development of the Thymus 132
•• Development of Parathyroid Glands 133
•• Development of Thyroid Gland 133
•• Time Table of Some Events in the Development of
Pharyngeal Arches 135
•• Embryological Explanation for Clinical Conditions or
Anatomical Observations 135
10. Skeletal System and Muscular System 137
Part 1: Skeletal System 138
•• Somites 138
•• Development of Axial Skeleton 139
•• Formation of Limbs 145
•• Joints 146
Part 2: Muscular System 147
•• Skeletal Muscle 147
•• Development of Muscular System 148
•• Time Table of Some Events 150
•• Clinical Case with Prenatal Ultrasound and Aborted Fetal Images:
Embryological and Clinical Explanation 151
11. Face, Nose and Palate 152
•• Development of the Face 152
•• Development of Various Parts of Face 153
•• Development of Palate 159
•• Time Table of Some Events in the Development of Face,
Nose and Palate 161
•• Embryological Explanation for Clinical Conditions or
Anatomical Observations 162
Contents xiii
12. Alimentary System—I: Mouth, Pharynx and Related Structures 163
•• Mouth 163
•• Teeth 164
•• Pharynx 168
•• Tongue 168
•• Derivatives of Oral Cavity 170
•• Salivary Glands 171
•• Time Table of Some Events Described in this Chapter 171
13. Alimentary System—II: Gastrointestinal Tract 172
•• Derivation of Individual Parts of Alimentary Tract 176
•• Rotation of the Gut 181
•• Fixation of the Gut 183
•• Time Table of Some Events Described in this Chapter 185
•• Embryological Basis for Clinical Conditions or
Anatomical Observations 185
14. Liver and Biliary Apparatus; Pancreas and Spleen; Respiratory System;
Body Cavities and Diaphragm 190
Liver and Biliary Apparatus 190
•• Liver and Intrahepatic Biliary Apparatus 190
•• Gallbladder and Extrahepatic Biliary Passages
(Extrahepatic Biliary Apparatus) 193
Pancreas and Spleen 197
•• Pancreas 197
•• Spleen 199
Body Cavities and Diaphragm 201
•• Body Cavities 201
•• Diaphragm 211
Respiratory System 214
•• Larynx 215
•• Trachea 217
•• Extrapulmonary Bronchi 217
•• Intrapulmonary Bronchi and Lungs 217
•• Embryological Basis for Clinical Conditions or
Anatomical Observations 224
15. Cardiovascular System 226
Part 1: Heart 227
•• Components of Blood Vascular System 227
•• Formation of Blood Cells and Vessels 227
•• Extraembryonic Blood Vascular System 228
•• Intraembryonic Blood Vascular System 228
•• Development of Heart 229
•• Development of Various Chambers of the Heart 230
•• Exterior of the Heart 239
•• Valves of the Heart 239
•• Conducting System of the Heart 240
•• Pericardial Cavity 240
Part 2: Arteries 243
•• Pharyngeal Arch Arteries and their Fate 243
•• Development of Other Arteries 246
Part 3: Veins 251
•• Visceral Veins 251
•• Somatic Veins 253
xiv Human Embryology
•• Veins of the Abdomen 255
•• Azygos System of Veins 257
Part 4: Fetal Circulation 258
•• Changes in the Circulation at Birth 260
Part 5: Lymphatic System 260
•• Time Table of Some Events Described in this Chapter 261
•• Embryological Basis for Clinical Conditions or
Anatomical Observations 261
16. Urogenital System 264
•• Development of Kidneys 265
•• Absorption of Lower Parts of Mesonephric Ducts into Cloaca 269
•• Development of the Ureter 270
•• Development of the Urinary Bladder 270
•• Development of the Female Urethra 271
•• Development of the Male Urethra 271
•• Development of the Prostate 272
•• Paramesonephric Ducts 273
•• Development of Uterus and Uterine Tubes 273
•• Development of Vagina 274
•• Development of External Genitalia 275
•• Development of Testes 278
•• Development of the Ovary 283
•• Fate of Mesonephric Duct and Tubules in the Male 284
•• Fate of Mesonephric Ducts and Tubules in the Female 285
•• Control of Differentiation of Genital Organs 286
•• Time Table of Some Events Described in this Chapter 287
17. Nervous System 288
•• Neural Tube and Its Subdivisions 289
•• Neural Crest Cells 292
•• Spinal Cord 293
•• Brainstem 296
•• Cerebellum 300
•• Cerebral Hemisphere 300
•• Autonomic Nervous System 308
•• Time Table of Some Events in Nervous System Development 311
•• Embryological Explanation for Clinical Conditions or
Anatomical Observations of Nervous System 312
18. Endocrine Glands 313
•• Classification of Endocrine Glands 313
•• Hypophysis Cerebri or Pituitary Gland 314
•• Pineal Gland 315
•• Adrenal Gland 315
•• Chromaffin Tissue 316
•• Time Table of Some Events Described in this Chapter 316
•• Embryological Explanation for Clinical Conditions or
Anatomical Observations in Eyeball 316
19. Development of Eye 318
•• Formation of the Optic Vesicle 318
•• Formation of Lens Vesicle 318
•• Formation of the Optic Cup 319
Contents xv
•• Derivation of Parts of the Eyeball 320
•• Accessory Structures of Eyeball 323
•• Time Table of Some Important Events Described in this Chapter 326
•• Embryological Explanation for Clinical Conditions or
Anatomical Observations in Eyeball 326
20. Development of the Ear 328
•• Internal Ear 328
•• Middle Ear 330
•• External Ear 330
•• Time Table of Some Events Described in this Chapter 334
•• Embryological Explanation for Clinical Conditions or
Anatomical Observations in Ear 334
21. Clinical Applications of Embryology 336
•• Gestational Period 336
•• Growth of the Embryo 336
•• Determining the Age of an Embryo 337
•• Further Growth of the Fetus 337
•• Determining the Age of a Living Fetus 339
•• Control of Fetal Growth 339
•• Causation of Congenital Anomalies (Teratogenesis) 342
•• Prenatal Diagnosis of Fetal Diseases and Malformations 343
•• Fetal Therapies 344
22. Embryology Ready Reckoner 345
•• Developmental Anatomy at a Glance 345
Index 353

•• Embryology: It is the study of the development of an individual before birth (prenatal period).
Embryo (G): (en = within; bruein= to swell or to be full); Logos = study
Natal = birth; Prenatal = before birth; Postnatal = after birth
•• Embryo: It is the developing individual during the first 2 months or 8 weeks of intrauterine life.
•• Fetus: It is the developing individual from the 3rd month or 9th week of intrauterine life to the time of birth.
•• Development before birth is called prenatal development, and that after birth is called postnatal development.
•• There are three stages in prenatal development. They are (1) preimplantation, (2) embryonic and (3) fetal periods.
•• Gonads: They are the sex organs that produce sex cells or gametes. The testis is the male gonad and the ovary is the
female gonad. Male gametes are called spermatozoa. Female gametes are called ova.
•• Gametogenesis: It is the process of production of gametes in gonads or sex organs. In males it is known as spermatogenesis
and in females as oogenesis.
•• Fertilization: It is the process of fusion of male and female gametes. It takes place in the uterine tube of female genital tract.
•• Zygote: It is the single cell that results from fertilization.
•• Development: It is a process where something grows or changes and becomes more advanced.
•• Growth: It is a quantitative change that increases the size.
•• Ontogeny: Complete life cycle of an organism.
•• Phylogeny: Evolutionary history of a group of organisms.
•• Differentiation: It is a qualitative change in structure for an assigned function.
•• Organizer: Any part of the embryo which exerts stimulus on an adjacent part.
•• Cell potency: It is the potential to differentiate into different cell types