Vlll CONTENTS 



CHAPTER VIII 



PAGE 

 THE CHANGES BETWEEN TWENTY-FOUR AND THIRTY-THREE HOURS OF 



INCUBATION 52 



The closure of the neural tube; the differentiation of the brain region; 

 the anterior neuropore; the sinus rhomboidalis; the fate of the primitive 

 streak; the formation of additional somites; the lengthening of the 

 fore-gut; the appearance of the heart and the omphalomesenteric 

 veins; organization in the area vasculosa. 



CHAPTER IX 



THE STRUCTURE OF CHICKS BETWEEN THIRTY-THREE AND THIRTY-NINE 



HOURS OF INCUBATION 59 



The divisions of the brain and their neuromeric structure; the auditory 

 pits; the formation of extra-embryonic blood vessels; the formation of 

 the heart; the formation of intra-embryomc blood vessels. 



CHAPTER X 



THE CHANGES BETWEEN FORTY AND FIFTY HOURS OF INCUBATION 75 



Flexion and torsion; the completion of the vitelline circulatory channels; 

 the beginning of the circulation of blood. 



CHAPTER XI 



EXTRA-EMBRYONIC MEMBRANES 80 



The folding off of the body of the embryo; the establishment of the 

 yolk-sac and the delimitation of the embryonic gut; the amnion and the 

 serosa; the allantois. 



CHAPTER XII 



THE STRUCTURE OF CHICKS FROM FIFTY TO FIFTY-FIVE HOURS OF IN- 

 CUBATION 93 



I. External Features. 

 II. The Nervous System. 



Growth of the telencephalic region; the epiphysis; the in- 

 fundibulum and Rathke's pocket; the optic vesicles; the lens; 

 the posterior part of the brain and the cord region of the neural 

 tube; the neural crests. 



III. The Digestive Tract. 



The fore-gut; the stomodaeum; the pre-oral gut; the mid-gut; 

 the hind-gut. 



IV. The Visceral Clefts and Visceral Arches. 

 V. The Circulatory System. 



The heart; the aortic arches; the fusion of the dorsal aortse; the 



cardinal and omphalomesenteric vessels. 

 VI. The Differentiation of the Somites. 

 VII. The Urinary System. 



