480 



THE HUMAN EMBRYO. 



defined neurenteric passage, NT, leading from the surface into the 

 cavity of the yolk-sac. 



The sections (Figs. 182-84) will render the relations of the 

 parts clearer. Fig. 182, which passes across the anterior part of 

 the head, shows the widely open neural groove, ng ; the fore-gut. 



Figs. 182-184. — Sections across the Human Embryo of the thirteenth day, 



represented in Figs. 180 and 181. (After v. Spee.) x 45. 

 Fig. 182. — Transverse section across the head end of the embryo. 

 Fig. 183. — Transverse section across the middle of the body. 

 Fig. 184. — Transverse section across the hinder end of the embryo and the 

 yolk-sac, the section passing through the neurenteric canal. 



AN", Inner or true amnion. CH, commencing notochord. E, epiblast of tlie 

 embryo. GF, fore-gut. G-T, mid-gut. H, hypoblast. M, mesoblast. ME, somato- 

 pleuric layer of mesoblast. MH, splanclmopleuric layer of mesoblast. NG, neural 

 groove. NT, neurenteric canal. YS, cavity of yolk-sac. 



GF, lined by hypoblast, and just shut off from the yolk-sac, YS ; 

 and the mesoblast, with its contained blood-vessels. Fig. 183 

 passes through the body region, and shows the commencing* 

 notochord, CH, as a thickened plate of hypoblast cells in the 

 mid-dorsal wall of the gut. 



Fig. 184 passes through the neurenteric canal, NT, which 



