1642 



HUMAN ANATOMY. 



Mucous coat 



1-4 cm. and in breadth from 6-16 mm. ; exceptionally their length may reach 10 cm. 

 or more. In general the size of the patches increases as the termination of the ileum 

 is approached. Each patch contains usually from twenty to thirty lymph-nodules, 

 although as many as sixty or less than ten may be present. The individual nodules 

 are commonly somewhat pear-shaped, and when well developed occupy both the 

 mucous and submucous coats, their smaller end almost reaching the epithelium and 

 their base the muscular tunic. The free surface of the patches is modelled by minute 

 pits, from .4-2 mm. in diameter, and low. intervening ridges ; the former mark the 

 positions of the component nodules, the latter that of the blending internodular 

 tissue. The villi and the crypts of Lieberkuhn are present over the areas between 

 the pits, although less developed than beyond the patch. In their minute structure 

 the lymph-nodes composing the patch closely correspond to the solitary nodules, the 



aggregated nodules be- 



FIG. 1396. ing blended into a con- 



tinuous mass by the less 

 dense adenoid tissue 

 which fills the spaces 

 between the individual 

 follicles. The entire 

 patch is defined from 

 the surrounding struc- 

 tures by an imperfect 

 capsule. 



The submucous 

 coat is lax, but not 

 enough so to allow the 

 j displacement of the val- 

 vtilae conniventes, ex- 

 cept at the lower part. 

 As in other segments 

 of the intestinal tube, 

 the submucosa contains 

 blood- and lymph-ves- 

 sels of considerable size 

 and the nerve-plexus of 

 Meissner. 



The muscular 

 coat, about .4 mm. 

 thick, consists of an 

 outer longitudinal and 

 an inner circular layer. 

 The latter is some two 

 or three times as thick as 

 the former and is pretty 

 regularly arranged. The 



Transverse section of injected small intestine, showing general distribution. X 55. thill longitudinal layer, 



thickest at the free bor- 

 der, is often Imperfect, especially at the attachment of the mesentery. The entire 



muscular coat diminishes in thickness from above downward. 



The serous coat, with the exception of that of the duodenum, completely sur- 

 rounds the mit except at the line of attachment of the mesentery, where the two layers 

 of peritoneum diverge, leaving an uncovered space between them just large enough 

 for the passage of the vessels and nerves. Its structure resembles that of the serous 

 coal i.l the stomach ( pagr 1627), and includes the tibro-elastic stroma covered with 

 ;lu- endothetium. 



The blood-vessels supplying the small intestine are distributed to the walls of 

 tin- tube in a manner closely agreeing with the arrangement found in the stomach 

 . IM-C I6a; i ; the same general plan applies also to the large intestine. The artfrifs^ 

 ulnch pass to the intestine between the peritoneal tolds constituting the mesentery, 



Muscular 

 coat 



