Fig. 47. — Surface view (dorsal) of an embryo of 33 hours. 

 (After Duval.) 



^w, head-fold of amnion. C, heart. (? iV", nerve ganglion. L M^ medul- 

 lary fold. LP, mesoblast that will segment into mesoblastic somites. /'/', primi- 

 tive streak Z' /', mesoblastic somites. S R^ sinus rhomboidalis. K2 and V%, 

 mid- and hind-brains, i' A^ auditory pits. V O M^ vitelline vein. 



140 



