MAMMALIA. 



229 



the head it exhibits a series of well-marked dilatations. The 

 foremost of these (vh) is the rudiment of the fore-brain, from the 

 sides of which there project the two optic vesicles (ab)\ the next 



A. 



B. 



ao 



FIG. 144. EMBRYO RABBITS OF ABOUT NINE DAYS FROM THE DORSAL SIDE. 



(From Kolliker.) 



A. magnified 22 times, and B. 21 times. 



ap. area pellucida ; rf. medullary groove ; //'. medullary plate in the region of the 

 future fore-brain; h". medullary plate in the region of the future mid-brain; vh. fore- 

 brain; ab. optic vesicle; mh. mid-brain; hh. and h'" . hind-brain; nw. mesoblastic 

 somite; stz. vertebral zone; pz. lateral zone; hz. and h. heart; ///. pericardial section 

 of body cavity; vo. vitelline vein; of. amnion fold. 



is the mid-brain (m/t), and the last is the hind-brain (////), which 

 is again divided into smaller lobes by successive constrictions. 

 The medullary groove behind the region of the somites dilates 

 into an embryonic sinus rhomboidalis like that of the Bird. 

 Traces of the amnion (<?/) are now apparent both in front of and 

 behind the embryo. 



