FOWL THIRD DAY 



539 



The body of the embryo lying over on its left side is <-los.-ly in- 

 vested by the .-minimi (am) while over this lies the thin roof (/.am) 

 constituting tin- serous membrane. At sa the two membranes 

 are united l>y tin- sem-amniotic connexion. In the me.soderm of the 

 two folds of splanchnopleure which are approaching one anth< -r to 

 floor in the alimentary canal (ent) are seen the two large vitelline 

 veins (v.v). The ventricle and the conus are seen cut longitudinally 

 in the wide coelomic space lyiii.^ to the right of the body of the 

 embryo. 



A section a little farther forward in the series has the appear- 

 ance shown in Fig. 237c. The definitive gut (ent) is completely 

 separated at this level from the yolk-sac, and corresponding with this 

 the two vitelline veins, which in sections farther back lay one on each 



ent. ani. /am. n.c.u 



som.< r 



sbm. 



Fie,. 237c. Transverse section a little in front of the hind end of the heart. 



"///, ainnion ; .1, dorsal aorta ; d.r, ductus venosus ; eit-t, alimentary canal ; ;."w. false ainnion ; /t.l, 

 anterior liver rudiment ; //.-_', posterior ditto ; A r , notochord ; p.c.v, posterior cardinal vein ; s-nn, soma- 

 Inpleure; .-//, splanchnoplenre ; >/-/, s]lanchnocoele ; V, ventricle. 



side of the yolk-stalk, are now completely fused into a large median 

 vessel, the ductus venosus (d.v), which is simply the backward 

 prolongation of the heart. The posterior liver rudiment, a blindly 

 ending pocket of the gut-wall projecting forwards ventral to the 

 ductus venosus, is seen in the section figured (li.2), although its com- 

 munication with the gut-wall is no longer visible, lying as it does 

 several sections farther back. At this level however a second pocket- 

 like outgrowth of the gut-wall has made its appearance (/t.l). This is 

 the anterior liver rudiment. It will he noticed that it lies dorsal to 

 the ductus venosus. In the coelomic space ventral to the ductus 

 venosus and liver rudiments, and quite isolated, is the rounded section 

 through the ventricular region of the heart ( V). 



In the sections studied so far the body-wall of the embryo is 

 widely open on its ventral side the opening heinir bounded by the 

 recurved edge along which the somatopleure of the body is continuous 



