994 



OF GENERATION. 



receives through the placenta, which is conducted to it by the vessels of the 

 umbilical cord. This state of things is represented in Figs. 266. 267, n n', o o'. 

 The allantois has a correspondence in origin with the Urinary Bladder ; but 

 it is only the lowest part of it, pinched off as it were, from the rest, which re- 

 mains as such. The duct by which it is connected with the abdomen gradually 

 shrivels ; and a vestige of this is permanent, forming the Urachus or suspensory 

 ligament of the Bladder by which it is connected with the Umbilicus. Before 

 this takes place, however, the Allantois is the receptacle for the secretion of 

 the Corpora Wolffiana, and of the true Kidneys, when they are formed ( 1007). 

 1002. It will be seen, from the succeeding diagram, that the Umbilical Cord 

 receives an investment from the Amnion, which forms a kind of tubular sheath 

 around it; it is continuous at the umbilicus with the integument of the foetus; 

 and at the point where the cord enters the placenta, it is reflected over its in- 

 ternal or fcetal surface. The Amnion (which thus forms a shut sac, like that 



Fig. 266. 



Fig. 267. 



Diagram of the Circulation in the Human Embryo and its Appendages, as seen The game, as seen 



in profile from the right side, at the commencement of the formation of the Pla- from the front, 



centa: a, venous sinus receiving all the systemic veins ; 5, right auricle; I/, left 

 auricle : c, right ventricle ; d, bulbus aorticus, subdividing into e, e', e", branchial 

 arteries;/, arterial trunk formed by their confluence ; g, vena azygos superior ; h, 

 confluence of the superior and inferior azygos ; j, vena cava inferior ; k, vena azy- 

 gos inferior; m, descending aorta; n, n, umbilical arteries proceeding from it; o, 

 umbilical vein ; q, omphalo-mesenteric vein ; r, omphalo-mesenteric artery, dis- 

 tributed on the walls of the vitelline vesicle t ; v, ductus venosus ; y, vitelline 

 duct ; z, chorion. 



of the pleura, arachnoid, &c.) contains a fluid known as the liquor amnii; this 

 consists of water holding in solution a small quantity of albumen and saline 

 matter, and resembling, therefore, very diluted serum. During the first two 

 months of gestation, the amnion and the inner lining of the chorion (which is 



