DEVELOPMENT OF THE LIVER. 



943 



cular than those of the left auricle. This condition lasts for some days after 

 birth, when the left heart gradually attains the superiority in thickness 

 which is usual in adults. 



784. The Altmcntai-i/ Canal has been shown ( 777) to have its origin in 

 the blastodermic vesicle ; being a portion pinched off (as it were) by the in- 

 folding of the splanchuopleure from that part of it which is just beneath the 

 spinal column of the embryo, whilst the remainder, which is at that time the 

 largest part of it, forms the vitelline or umbilical vesicle. In its earliest 

 form it is merely part of a long narrow tube (Fig. 348, ra), nearly straight, 



FIG. 348. 



Embryo of Dog, 25 days after last copulation : a, a, nostrils ; 6, 6, eyes ; c, c, first visceral arches, form- 

 ing the lower jaw ; d, d, second visceral arches ; e, right auricle ; /, left auricle ; g, right ventricle; ft, left 

 ventricle; i, aortic bulb ; k, k, liver, between the two lobes of which is seen the divided orifice of the 

 omphalo-mesenterie vein; /.stomach; m, intestine, communicating with the umbilical vesicle n, n; 

 o, o, corpora Wolffiana; p, allantois; q, g, anterior extremities; r, r, posterior extremities. 



and communicating with the umbilical vesicle (n, n) at about the middle 

 of its length ; thus it may be regarded as composed of the union of two divi- 

 sions, an upper and a lower. At first, neither mouth nor anus exists; but 

 these are formed early in the second month, if not before. The tube gradu- 

 ally manifests a distinction into its special parts, oesophagus, stomach, small 

 intestine, and large intestine; and the first change in its position occurs in 

 the stomach, which, originally disposed in the line of the body, afterwards 

 takes an oblique direction. The curves of the large and small intestine pre- 

 sent themselves at a later period. It is at the lower part of the small intes- 

 tine, near its termination in the large, that the entrance of the vitelline duct 

 persists; and a remnant of this canal is not unfrequently preserved through- 

 out life, in the form of a small pouch or diverticulurn from that part of the 

 intestine. 



785. In immediate connection with the intestinal tube, we find the first 



