It) 



THE ANATOMY OF YERTEBRATED ANIMALS. 



even in this early stage, a clear distinction is drawn between 

 the skull and the spinal column. 



Y^a i. — Successive stages of the development of the "^ead of a Chick. I, II, III, first, sec- 

 ond, and third cerebral vesicles ; /a, vesicle of the cerebral hemisphere ; 76, vesicle of 

 the third ventricle; a, rudiments of the eyes and optic nerves; 6, of the ears; c of th« 

 olfactory organs; d^ the infundibulum ; e, the pineal gland; c, protovertebrje ; h. noto- 

 chord ; 1, 2, 8, 4, 5, visceral arches ; V, YII, VIII, the trigeminal portio dura, and ninth 

 and tenth pairs of cranial nerves ; ^, the nasal process ; l^ the maxillary process ; ec, tlie 

 first visceral clelt. A, B, upper and under views of the head of a Chick at the end of 

 the second day. 0, side-view at the third day. D. side-view at seventy-five hours. 33, 

 aide-view of the head of a Chick at the fifth day, which has been subjected to slight press- 

 xire. F, head of a Chick at the sixth day, viewed from below. 



