374 THE DIGESTIVE SYSTEM 



ply the adjacent portion of the inner layer of the muscular coat, but most 

 of them pass to the mucous membrane, in which a plexus lies just within 

 the muscularis mucosse and distributes its branches to the capillaries 

 about the intestinal glands and to the intestinal villi. 



The artery of the villus enters at its base, and distributing capillaries 

 along its course, forms in the distal part of the villus an abundant 

 capillary network from which efferent venules return by a similar course. 

 The artery, however, is found near the axis, the venules near the per- 

 iphery of the villus. 



Branches from the submucous and mucous arterial plexuses also 

 supply capillaries to the duodenal glands in the duodenum as well as to 

 the solitary and agminated lymph nodules. About each of the lymph 

 nodules they form circular anastomoses, from which radial capillaries 

 are distributed within the nodule. 



The veins pursue a course exactly similar to that of the arteries. On 

 their way to the mesenteric vessels they form mucous, submucous, intra- 

 muscular, and subserous plexuses, and drain into the portal system. 

 The portal vein and its main tributaries lack valves. Valves are present 

 only in the smaller tributaries, beginning in the tunica muscularis 

 throughout the digestive tube and prevailing generally in the mesenteric 

 veins. 



Lymphatics. The lymphatics or lacteals of the small intestine be- 

 gin in the distal part of the villi as lymphatic capillaries, each having, 

 as a rule, a pouched, blind extremity. 'During the digestion of fats 

 they become distended with a whitish fatty lymph called chyle. At their 

 origin the lacteals are frequently branched, or they may even form 

 a scanty anastomosis. They finally unite to form a central lacteal in 

 the axis of the villus, which empties into a rich plexus about the intes- 

 tinal glands, or like the efferent vessels of this plexus, they may pass 

 directly to the larger lymphatic vessels of the submucosa. 



From the submucous plexus numerous efferent lymphatic vessels 

 penetrate the muscular coat, receiving the lymph from the vessels of 

 the intramuscular septum. They empty into the larger lacteal vessels 

 of the mesentery which are intimately connected with numerous mesen- 

 teric lymph nodes. In the mucosa and submucosa the lacteals form 

 sinuses which surround the bases of the solitary and agminated nodules. 

 Thus, much of the chyle is permitted to come into relation with the 

 parenchyma of these organs before leaving the intestinal mucosa. 



Nerve Supply. The nerve supply of the intestine is exactly similar 

 to that of the stomach. The non-medullated fibers form an intra- 



