476 



THE DIGESTIVE APPARATUS IN MAMMALIA. 



The vesicles are usually closed ; though it is supposed they open at intervals to 

 discharge their secretion. The mucous and submucous coats of the intestine 

 are intimately adherent and highly vascular, opposite the Peyerian glands.) 



Fig. 278. 



Fig. 279. 



PERPENDICULAR SECTION THROUGH THI'^ INTESTINAL WALL TO SHOW A SOLITARY FOLLICLE. 



a, Lieberkiihnian glariils ; 6, solitary follicle; c, lacteal vessels stirmunding, but not ]ienetrating, 

 the follicles ; d, large efferent vessels, provided with valves. 



4. Vessels and nerves. — The small intestine receives its arteries almost ex- 

 clusively from the great mesenteric artery. One, which goes to the duodenum, 

 comes from the cceKac trunk. These arteries form a submucous network, from 

 which branches pass inwards and outwards, the first to 

 the muscular and serous tunics, the second to the glands 

 and the villi. A tubular network surrounds each 

 Lieberkiihnian gland, and is observed in each villus ; 

 while a spherical reticulation surrounds each solitary 

 follicle, loops being given off which penetrate nearly to 

 the centre of the follicle. 



The veins have the same arrangement, and finally 

 enter the vena portse. 



The lymphatics constitute three superposed networks 

 in the mucous membrane. The first is situated around 

 the glandular orifices ; it receives the central lacteal from 

 each villus ; the second is placed between the glandular 

 and the muscular layer of the mucous membrane ; the 

 third lies in the deep portion of the membrane, and 

 communicates with the meshes encircling the solitary 

 glands. The largest emergent vessels from these three 

 networks pass through the wall of the intestine, accom- 

 panying the blood-vessels between the layers of the mesentery, enter the mesenteric 

 glands, and terminate in the reservoir of Pecquet {receptaculum chyli). There 

 is another lymphatic network in the muscular tunic of the intestine. 



VILLI OF INTESTINE, WITH 

 THEIR CAPILLARY PLEXUS 

 INJECTED. 



