324 



EMBRYOLOGY. 



more and more flattened, and in the adult become so thin that 

 formerly the presence of an epithelial covering was wholly denied. 

 Then they assume a condition similar to that of endothelial cells ; 

 as in the case of the latter, their boundaries are demonstrable only 

 after treatment with a weak solution of silver nitrate. 



C. The Glands of the Small Intestine : Liver and Pancreas. 

 (1) The Liver. 



In the section which treats of the liver we must enter upon a dis- 

 cussion not only of the development of the parenchyma of the gland, 

 but also of the various hepatic ligaments the 

 lesser omentum, the ligamentum suspensorium, 

 etc. ; in fact, we must begin with the latter 

 because they are developed out of a structure 

 a ventral mesentery which is ontogenetically 

 older than the liver itself. In view of the 

 manner in which the body-cavity arises, as a 

 pair of cavities, such a structure ought to be 

 found along the whole length of the ventral 

 side of the alimentary canal in the s :me manner 

 as on its dorsal side. Instead of that, it is found 

 only at the anterior region of the alimentary 

 canal, along a tract which extends from the 

 throat to the end of the duodenum. 



This ventral mesentery acquires a special 

 significance, because several important organs 

 take their origin in it ; in front, the heart, 

 together with the vessels that bring the blood 

 back to it the terminal parts of the venae 

 omphalomesentericae and of the vena umbili- 

 is; immediately behind the latter, the liver with its outlet and 

 its blood-vessels. 



The part which, during an early stage of development, encloses the 

 heart is called mesocardium anterius and postering ; we shall return 

 to it later in considering the development of that organ. The 

 portion (fig. 184) which joins this behind [caudad] has been hitherto 

 less regarded by embryologists. Since it stretches from the lesser 

 curvature of the stomach and the duodenum (du) to the anterior 

 [ventral] wall of the trunk, it may be especially designated as the 

 ventral gastric and duodenal mesentery, or, under a more compre- 



fig. 184. Diagram (view 

 of a cross section) to 

 show the original re- 

 lations of duodenum, 

 pancreas, and liver, 

 and of the ligamentous 

 structures belonging to 

 them. 



II K, Posterior wall of the 

 trunk ; du, duodenum ; 

 p, pancreas ; l t liver ; 

 dms, dorsal mesentery ; 

 Ihd, ligamentum hepa- 

 to duodenale ; It, liga- 

 mentum suspeusorium 

 hepatia. 



