THE INTESTINES. 



405 



smallest scarcely measure more than some few hundredths of an inch square ; 

 while the diameter of the largest increases to 1 J inch. 



(Each of these patches is composed of a group of small, round, whitish 

 vesicles, covered with mucous membrane; these vesicles consist of a 



Fig. 200. 



Fig. 201. 



PERPENDICULAR SECTION THROUGH THE INTESTINAL WALL TO SHOW A SOLITARY FOLLICLE. 



a, Lieberfciihnian glands ; 6, Solitary follicle ; c, Lacteal vessels surrounding, but 



not penetrating, the follicles ; c?, Large efferent vessels, provided with valves. 



moderately-thick external capsule, having no excretory canal, and containing 

 a similar secretion to that in the solitary follicles. They are surrounded 

 by a zone or band of simple follicles, and the 

 spaces between them are covered with villi. 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, oppo- 

 site the Peyerian glands.) 



4. Vessels and nerves. The small intestine 

 receives its arteries almost exclusively from the 

 great mesenteric artery. One, which goes to the 

 duodenum, comes from the coeliac 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 sur- 

 rounds each Lieberkuhnian gland, and is observed 

 in each villus ; while a spherical reticulation sur- 

 rounds each solitary follicle, loops being given off VILLI OF INTESTINE, 

 which penetrate nearly to the centre of the THEIR CAPILLARY 

 follicle. INJECTED. 



The veins have the same arrangement, and finally enter the vena porta>. 

 29 



WITH 

 PLEXUS 



