104 
THE DEVELOPMENT OF THE CHICK 
Fig. 59. — Embryo of 7s from above drawn 
in balsam with transmitted light. x 30. 
a.c.s., Anterior cerebral suture. ceph. 
Mes., Cephalic Mesoblast. EF. G., Fore-gut. 
N’ch., Notochord. n.'T., Neural tube. op. 
Ves., Optie vesicle. Pr’a., Proamnion. — pr. 
str., Primitive streak. s 2, s 7, Second and 
seventh somites. V. 0. m., Omphalo-mes- 
enteric vein. 
