208 



STUDY OF YOUNG CHICK EMBRYOS. 



structures and relations which appear. A little piece of the ventricular limb of 

 the heart with its double walls, m.ht,endo, still appears. The section is, strictly 

 speaking, beyond the venous end of the heart and passes through the sinus venosus 

 Si. V, which is formed by the union of the omphalo-mesaraic veins entering the 

 body of the embryo from the splanchnopleure of the yolk-sac, or, in other words, 



endo. 



Ent. 



FIG. 157. SECTION OF CHICK EMBRYO WITH ABOUT TWENTY-EIGHT SEGMENTS. TRANSVERSE SERIES 92, 



SECTION 165. 



Am, Amnion. Ao, Aorta, card, Cardinal vein. Cho, Chorion. Cos, Cce', Ccelom. EC, Ectoderm, endo 

 Endothelial heart. Ent, Entoderm. Li, Liver, mes, Mesoderm. m.ht, Muscular heart. ' msth, Meso- 

 thelium. My, Primitive segment, nch, Notochord. raph, Raphe of amnion. Si. V, Sinus venosus of 

 heart. Som, Somatopleure. Sp.c, Spinal cord. Spl, Splanchnopleure. Ve, Vein, x, Accumulation of 

 mesodermic tissue about the omphalo-mesaraic vein. X 50 diams. 



from the area vasculosa. ]n the splanchnopleure, Spl, there is a thickening, x, 

 ^derm which .narks the crossing of the veins from the yolk-sac to ' the 

 The entoderm of the embryo forms a tube, Ent, which 

 so-ventral diameter. The entoderm itself is quite 

 From the ventral side of >he^ entoder- 







