THE SMALL INTESTINE. 



after supplying the serous coat, penetrate the muscular tunic to reach the submucosa. 

 Within the latter branches arise which, in conjunction with those directly given off 

 during the passage through the muscular coat, supply the muscular tissue. The more 

 important and larger arterial twigs from the vessels of the submucosa enter the 

 mucous coat, in which some break up into capillaries forming net-works surrounding 

 the gland-tubules and supplying the muscular and stroma tissue ; others pass directly 

 towards the villi, which they enter and supply by capillary net-works occupying the 

 periphery of the projections. The veins of the intestinal walls commence within the 

 mucosa beneath the epithelium and, gradually enlarging as they descend, become 

 tributary to the larger veins within the submucosa. The latter follow the arteries in 

 their passage through the muscular tunic, uniting to form the larger emergent venous 

 channels which accompany the arterial trunks between the peritoneal folds. 



The lymphatics of the small intestine, long known as the lacteals from their 

 conspicuous milky appearance when filled with emulsified fat during certain stages of 

 digestion, begin as the absorbent or chyle-vessels within the villi. In addition to 

 these, radicles commence within the stroma-tissue of the mucosa, in which the lym- 



Branch of mesenteric artery 

 Mesenteric vein 



Lymph-node 



Lymphatics 



Cut edge of removed 

 peritoneum 



Nerves 



Portion of small intestine and mesentei 



quicksilver. 



,-, showing arteries, nerves, and lymphatics; latter have been injected with 

 Anterior layer of mesentery has been removed. 



phatics form a plexus in the plane of the muscularis mucosae. From the latter tribu- 

 taries descend to the larger plexus within the submucosa, which is characterized by 

 channels of irregular form and calibre containing numerous valves. The emergent 

 lymphatics form larger vessels within the serous coat, which pass to the lymph- 

 nodes situated between the peritoneal layers ; from these smaller lymphatic masses 

 efferent vessels converge to the larger mesenteric lymph-nodes at the root of the 

 mesentery. 



The nerves supplying the small intestine, derived from the solar plexus and 

 consisting of both medullated and non-medullated fibres from the cerebro-spinal and 

 sympathetic systems, closely follow the disposition observed in the stomach (page 

 1 628). After piercing the other longitudinal layer they form the intramuscular plexus 

 of Auerbach, consisting of both varieties of fibres and microscopic sympathetic gan- 

 glia. The nerves continue obliquely through the circular muscular layer and form 

 within the submucous coat the plexus of Meissncr. From this plexus non-medullated 

 fibres enter the mucous coat and are distributed as periglandular and subepithelial 

 net-works, as well as supplying the muscular tissue, in which, according to Berkley, 

 additional special end-organs exist. Within the villi a rich plexus of non-medullated 



