FOWL— THIED DAY 



539 



The body of the embryo ' lying over on its left side is closely in- 

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

 constituting the serous membrane. At sa the two membranes 

 are united by the sero-amniotic connexion. In the mesoderm of the 

 two folds of splanchnopleure which are approaching one another 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 lying to the right of the body of the 

 embryo. 



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

 ance shown in Pig. 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 



li2 



j£l ent am. fqm. p.c.v. 



div 



sOra.. 



Fig. 237c. — Transverse section a little in front of the hind end of the heart. 

 am, amnion ; A, dorsal aorta ; d.v, ductus venosus ; ent, alimentary canal ; /.am, false amnion ; li.l, 

 anterior liver rudiment ; H.2, posterior ditto ; N, notochord ; p.c.v, posterior cardinal vein ; som, soma- 

 topleure ; spl, splanchnopleure ; splc, splanchnocoele ; 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 (li.l). This is 

 the anterior liver rudiment. It will be 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 being bounded by the 

 recurved edge along which the somatopleure of the body is continuous 



