326 EMBRYOLOGY. 



hensive title, as ventral alimentary mesentery (Ihd + Is). It has 

 been described by KOLLIKER on sections of Rabbit embryos as liver- 

 ridye (Leberwulst), and by His in his " Anatomie menschlicher 

 Embryonen r> as preliepaticus (Vorleber) ; it has the form of a mass 

 of tissue rich in cells, which inserts itself between the wall of the 

 belly and the regions of the intestine previously mentioned. In 

 cross sections through human and mammalian embryos there are 

 encountered in it the capacious vense omphalomesentericse. As far 

 as a mesocardium and a mesogastrium anterius are developed in 

 Vertebrates, the body-cavity appears even subsequently as a paired 

 structure. 



The cross section through a Selachian embryo (fig. 185) shows this 

 distinctly. The duodenum (du) is enclosed in the connective -tissue 

 mesentery, which reaches from the aorta (ao) to the front [ventral] 

 wall of the trunk ; dorsally the pancreas (pan) is budded forth from 

 its wall, ventrally the liver (hp.d). 



The liver begins to be developed very early in the ventral me- 

 sentery (liver-ridge or prehepaticus), and in this exhibits, as will 

 appear later, two modifications, which are, however, unessential ; for 

 sometimes it appears in the form of a single, sometimes as a paired 

 evagination of the epithelial lining of the ventral wall of the duo- 

 denum. 



The first is the case, for example, in the Amphibia and Selachii. 

 In Bombinator (fig. 159), as GOETTE has shown, the liver arises as a 

 broad ventrally directed evagination of the intestine, which lies im- 

 mediately in front of the accumulation of yolk-material. The liver 

 remains permanently in this simplest form in the case of Amphioxus 

 lanceolatus, in which it is located immediately behind the gill-region 

 as an appendage of the intestinal canal. 



In the case of Birds and Mammals, on the contrary, the funda- 

 ment of the liver is from the beginning double. As has been known 

 since the investigations of REMAK, in the case of the Chick (fig. 186) 

 on the third day of incubation, two sacs (I) grow out of the ventral 

 wall of the duodenum immediately behind the spindle-shaped 

 stomach (<St). They grow into the broad cell-mass of the ventral 

 mesogastrium (the Leberwulst), one passing forward to the left, the 

 other backward to the right, and thereby embrace from above the 

 vena omphalomesenterica on its way to the heart. The process in. 

 Mammals is somewhat different. According to the observations of 

 KOLLIKER in the case of the Rabbit, the primitive hepatic tube of 

 the left side is formed in the embryo of ten days, to which a right 



