108 



DEVELOPMENT OF THE INTESTINES. 



mouth, that corresponding to the anus, and along the entire vertebral 

 line. While this separation is taking place, masses of cells from the 

 mucous layer are left between the two laminae; from these the liver 

 and the Wolffian bodies are formed. When thus separated from the 

 serous layer, the mucous layer forms a completely closed sac containing 

 the yolk-nucleus. Shortly, over its whole external surface, there is de- 

 veloped a fine layer of cells, which at the above-mentioned points of attach- 

 ment, becomes continuous with a similar layer of cells simultaneously 

 developed along the inner surface of the serous lamina ; and from these 

 united layers of cells are subsequently formed the peritoneal sac and the 

 mesentery. By the absorption of the membranes at the points correspond- 

 ing to the cavity of the mouth and the anus, the sac formed by the 

 mucous layer is opened, and the character of the Alimentary canal is 

 thus assumed by it. During the subsequent growth of the intestine the 



Fig. 24* 



* Fig. 24. An embryo dog representing the junction of the umbilical vesicle with the 

 intestinal canal, a, rudimentary nostrils; b, rudimentary eyes; c, the first visceral arch; d, 

 the second visceral arch ; e, the right,/, the left auricular appendage ; </, the right, h, the left 

 ventricle of the heart; z, the aorta; k, the liver, between the two lobes of which is perceived 

 the divided orifice of the omphalo-mesenteric vein ; Z, the stomach ; /, the intestine, com- 

 municating with the umbilical vesicle n ; o, the Wolffian bodies ; j>, the allantois ; 7, the 

 upper extremities; r, the lower extremities. After Bischoff. (Entwick. des Hunde-eies.) 



