VESSELS AND NERVES OF THE SMALL INTESTINE. 367 



The lacteal plexuses, which are abundant in the whole extent of the 

 intestine, are especially rich where they sui-round the follicles of Peyer's 

 glands (fig. 204), often forming sinuses as in the case of the solitary 

 follicles above described. 



In all, from twenty to thirty of these oblong patches may in general 

 be found ; but in young persons dying in health, as many as forty-five 

 have been observed. They are larger and placed at shorter distances 

 from each other, in the lower part of the ileum ; but in the upper portion 

 of that intestine and in the lower end of the jejunum, the patches occur 

 less and less frequently, become smaller, and are of a nearly circular 

 form ; they may, however, be discovered occasionally in tlic lower por- 

 tion of the duodenum. 



Still smaller irregularly shaped clusters of these follicles are some- 

 times found scattered throughout the intestine. 



It was fonneiiy presumed without question that Peyer's and tlie other closed 

 follicles in the alimentary tract constituted a peculiar capsular form of secreting 

 glands ; but there is now no doubt that they are more immediatelj^ connected 

 A^-ith the Ijnnphatic system, and their similarity on a small scale to the stmctm-e 

 of the lymphatic glands is immistakeable. It is found that tlie glands of Peyer 

 are best marked in the young subject. After middle life they become less obvious, 

 and are said to disajipear completely in advanced age. 



Vessels and Nerves.— The branches of the mesenteric artery, ha^-ing reached 

 the attached border of the intestine, pass round its sides, dividing into numerous 

 ramifications and frequently anastomosing at its free border. Most of the larger 

 branches run immediately beneath the serous coat ; they then pierce the mus- 

 cular coat, supplying it with vessels as they pass, and ramify in the submucous 

 areolar laj-er. so as to form a close network, from which still smaller vessels pass 

 on into the mucous coat, and terminate in the capillary network of the folds, 

 villi, and glands of that membrane. The fine capillaries of the muscular 

 coat are an-anged in two layers of oblong meshes, which con-espond in dii-ection 

 with the longitudinal and cii'cidar muscular fibres. The veins accompany the 

 arteries. 



The Ii/))q)hatii's of the intestine (lacteals) may he conveniently distinguished as 

 those of the mucous membrane, and tliose of the muscular coat. Those of the 

 mucous membrane form a copious plexus (fig. 26-1) which receives the central 

 vessels of the villi and pervades both the mucous and submucous layers — in the 

 latter being of considerable size, and fonning, as before mentioned, a close plexus 

 or a sinus around the base of each lymphoid follicle ; but there is not, in 

 the human subject at least, the same distinct division into two strata which has 

 been found in the stomach (Teichmann). From the submucous plexus larger 

 vessels proceed and pierce the muscular coat to open into the lymphatics which 

 lie under the peritoneal coat, and which are esi^eciallj' developed along a nan-ow 

 strip at the attachment of the mesenterj-. "Witli regard to the lymjihatics of the 

 muscular coat, the main plexus is situated between the circular an<l longitudinal 

 layers of fibres ; and there are likewise close plexuses threading- the whole 

 thickness of the muscular wall. These muscular lymphatics are in complete 

 continuity with those of the mucous membrane, and iiaes into larger vessels at 

 the mesenteric border, whicli again run into the lacteal vessels of the mesentery. 

 To these absorbents of the muscular coat Auerbach gives the name of " inter- 

 laminar plexus." * 



The nerves of the small intestine are chiefl}^ derived from the superior 

 mesenteric plexiis. This plexus is formed superiorly by neiwous branches, 

 of which those in the middle come from the celiac plexus, and the lateral 

 ones proceed directly from the semilunar ganglion, and it also receives con- 

 tributions from the vagus nerve. The plexus and j^lexiform branches into 

 which it divides cling at fii'st very closely to the larger divisions of the 

 superior mesenteric artery, and, dividing similarly with the ramifications 

 * Virchow's Archiv, vol. xxxiii, p. 310. 



