298 THE DIGESTIVE ORGANS. 



The nerve-fibers following the hepatic arteries are in every respect like 

 the vascular nerves in other glands. Some of the terminal branches 

 seem, however, to end on hepatic cells. The nerve-fibers following 

 the bile-ducts may be traced to the smaller and medium-sized 

 ducts, forming a network about them, and ending here and there 

 in small twigs on the outer surface of the cells, and occasionally, 

 it would seem, between the epithelial cells lining the ducts. The 

 suggestion seems warranted that these terminal fibrils are the end- 

 ings of. sensory nerves. Some of the nerve-fibers following the 

 bile-ducts may be traced into the hepatic lobules. The intralobu- 

 lar plexus is formed, therefore, by the terminal branches of the non- 

 medullated nerve-fibers accompanying the portal and hepatic ves- 

 sels and the bile-ducts. In the wall of the gall-bladder are found 

 numerous small sympathetic ganglia formed by the grouping of the 

 cell-bodies of sympathetic neurones (Dogiel). The neuraxes of these 

 innervate the nonstriated muscle of this structure. Large, medul- 

 lated nerve-fibers may be traced through these ganglia which 

 appear to end in free sensory endings in and under the epithelium 

 lining the gall-bladder (Huber). 



In the human embryo the liver originates from the intestine 

 during the second month as a double ventral diverticulum. Later 

 solid trabecular masses are developed which then unite and become 

 hollow. At this stage the whole gland is uniform in structure, as 

 a division into lobules does not take place until later. The bile 

 capillaries are surrounded by more than two rows of cells. In this 

 stage the embryonal liver suggests a condition which is permanent 

 during the life of certain animals. Only later when the venae ad- 

 vehentes, which later represent the branches of the portal vein, 

 penetrate the liver, is there a secondary division into lobules (about 

 the fourth month), by which process the primitive type gradually 

 changes to that characteristic of the adult. 



E. THE PANCREAS, 



Like the liver, the pancreas is an accessory intestinal gland, and 

 originates as a diverticulum of the intestine. It remains in perma- 

 nent communication with the intestine by means of its duct the 

 pancreatic or Wirsungia^ duct. The pancreas is composed of 

 numerous microscopic lobules, surrounded by connective tissue 

 which penetrates into the lobules and between the alveoli and 

 is accompanied by vessels and nerves. The secretory portion 

 of the organ may be regarded as a compound, branched alveo- 

 lar gland, the general structure of which is shown in Fig. 

 240, the alveoli forming the principal portion of the gland. 

 The epithelial walls of the alveoli consist of a number of 

 secretory cells, whose appearance varies according to the func- 

 tional state of the organ. The basilar portions of the cells present 



