r 



CONTENTS 



PACE 



INTRODUCTION i 



CHAPTER I. THE GERM CELLS: MITOSIS, MATURATION AND FERTILIZATION 7 



The Ovum 7 



Ovulation and Menstruation 10 



The Spermatozoon 1 1 



Mitosis and Amitosis 12 



Maturation 14 



Fertilization 20 



CHAPTER II. CLEAVAGE AND THE ORIGIN OF THE GERM LAYERS 24 



Cleavage in Amphioxus, Amphibia, Reptiles and Birds 24 



Cleavage in Mammals 27 



The formation of Ectoderm and Entoderm (Gastrulation) 28 



Origin of the Mesoderm, Notochord and Neural Tube 30 



The Notochord 36 



CHAPTER III. THE STUDY OF CHICK EMBRYOS 37 



Chick Embryo of Twenty Hours 37 



Chick Embryo of Twenty-five Hours (7 Segments) 39 



Transverse Sections 41 



Chick Embryo of Thirty-eight Hours (17 segments) 45 



General Anatomy 45 



Transverse Sections 48 



Derivatives of the Germ Layers 55 



Chick Embryo of Fifty Hours (27 segments) 5 6 



General Anatomy 56 



Transverse Sections 61 



Extra-embryonic Structures 66 



CHAPTER IV. HUMAN EMBRYOS AND FETAL MEMBRANES 7<> 



Fetal Membranes of the Pig Embryo 7 



The Umbilical Cord 72 



Early Human Embryos and Their Membranes 73 



Anatomy of a 4.2 mm. Human Embryo 81 



The Age of Human Embryos 89 



CHAPTER V. THE STUDY OF PIG EMBRYOS 9' 



The Anatomy of a 6 mm. Pig Embryo 9 1 



External Form and Internal Anatomy 91 



Transverse Sections 105 



The Anatomy of 10-12 mm. Pig. Embryos 114 



External Form and Internal Anatomy 114 



Transverse Sections 127 



CHAPTER VI. THE DISSECTION OF PIG EMBRYOS: DEVELOPMENT OF THE FACE, PALATE, 



TONGUE, SALIVARY GLANDS, AND TEETH '39 



Directions for Dissecting Pig Embryos 139 



Dissections of 18-35 mm - Embryos '42 



Development of the Face 146 



Development of the Palate '48 



Development of the Tongue '5' 



Development of the Salivary Glands '53 



Development of the Teeth 1 54 



CHAPTER VII. THE ENTODERMAL CANAL AND ITS DERIVATIVES 161 



The Pharyngeal Pouches and their Derivatives '62 



The Thyreoid Gland 166 



The Larynx, Trachea and Lungs '66 



vii 



