X.] THE CRANIAL FLEXURE. 333 



dfjj. splanchnic mesoblast; ph. pericardial section of body- 

 cavity ; ahh. muscular wall of heart ; ihh. epithelioid layer of 

 heart ; mes. lateral undivided mesoblast ; sw. fold of hypo- 

 blast which will form the ventral wall of the pharynx ; sr. 

 commencing throat. 



The later stages in the development proceed in the 

 main in the same manner as in the Bird. The cranial 

 flexure soon becomes very marked, the mid-brain form- 

 ing the end of the long axis of the embryo (Fig. 108). 

 The sense organs have the usual development. Under 

 the fore -brain appears an epiblastic involution giving 



FIG. 108. 



ADVANCED EMBRYO OF A RABBIT (ABOUT TWELVE DAYS) 1 . 



mb. mid-brain ; ih. thalamencephalon ; ce. cerebral hemisphere ; 

 op. eye ; iv.v. fourth ventricle ; moc. maxillary process ; md. 

 mandibular arch ; Jiy. hyoid arch ; fl. fore-limb ; hi. hind- 

 limb ; urn. umbilical stalk. 



1 .This figure was drawn by Mr Weldon. 



