CONTEXTS vii 



PAGE 



The Turning of the Embryo and the Embryonic Flexures 133 



II. Origin of the Embryonic Membranes 135 



Origin of the Amnion and Chorion 135 



The Yolk-sac 143 



Origin of the Allantois 143 



Summary of Later History of the Embryonic Membranes . 145 



III. The Xervous System 147 



The Brain 147 



The Neural Crest and the Cranial and Spinal Ganglia 156 



IV. The Organs of Special Sense (Eye, Ear, X'ose) . 164 



The Eye ^ . 164 



The Auditory Sac 168 



The Nose (Olfactory Pits) 169 



V. The Alimentary Canal and its Appendages . . . 170 



The StomodoEum 173 



The Pharynx and Visceral Arches 173 



(Esophagus and Stomach 179 



The Liver 179 



The Pancreas 181 



The Mid-Gut 181 



Ancd Plate, Hind-gut, Post-anal gut and Allantois 182 



VI. History of the Mesoderm 183 



Somites 183 



The Intermediate Cell-mass 190 



The Vascular System 197 



VII. The Body-cavity and Mesenteries 205 



PART II 



THE FOrRTH DAY TO HATCHING, ORGANOGENY, 

 DEVELOPMENT OF THE ORGANS 



CHAPTER VII. THE EXTERXAL FORM OF THE EM- 

 BRYO AXD THE EMBRYONIC :\IEMBRAXES 211 



I. The External Form 211 



General 211 



Head 213 



II. Embryonic Membranes . . . 216 



General 216 



The Allantois 220 



The Yolk-sac 225 



The Amnion 231 



Hatching . . 232 



