302 



THE DIGESTIVE ORGANS. 



again as areas of embryonic gland tissue. From their structure 

 and distinct blood supply, and the fact that no ducts have been 

 traced into these areas, it seems probable that they are small masses 

 of cells forming a secretion which passes into the blood-vessels in- 

 ternal secretion. 



The blood-vessels after entering the gland, divide into smaller 

 branches in the lobules, and finally break up into capillaries which 



Fig. 243. Scheme showing relation of three adjoining alveoli to excretory duct, 

 illustrating origin of centro-acinal cells. 



< 



,. 



? .<$: 



.>,',*. ?'.> . 



Blood capillary. 



Alveolus or gland. 



Area of Langer- 

 hans. 



Fig. 244. From section of human pancreas, showing gland alveoli surrounding an area 



of Langerhans. 



encircle the secreting alveoli. The blood-vessels do not follow the 

 course of the ducts so regularly as in the salivary glands (Flint). 

 The meshes of the capillary network are not all of the same size. 

 In some regions they are so wide that quite large areas of the 

 alveoli are without blood-vessels. 



The nerves of the pancreas have been investigated by Cajal and 

 Sala (91) and Erik Muller (92), who find in this gland large num- 

 bers of nonmedullated nerve-fibers, some coming from sympathetic 



