170 



NORMAL HISTOLOGY. 



In structure, the component lymph-nodules correspond to the solitary nodules, 

 the aggregated nodules being blended into a continuous mass by the less dense 

 lymphoid tissue filling the spaces between the individual nodules. The entire 

 patch is defined from the surrounding tissues by an imperfect fibrous capsule. 

 The submucous coat of the small intestine, although lax, does not 

 allow displacement of the plicae circulares, except in the lower part of the 

 tube. In addition to most of Brunner's glands and the lymph-nodules, the 



submucosa contains blood- 

 vessels and lymphatics of 

 considerable size and the 

 nerve-plexus of Meissner. 



The muscular coat, 

 about .4 mm. thick, consists 

 of an inner circular and an 

 outer longitudinal layer of 

 involuntary muscle. The 

 circular stratum is some two 

 or three times as thick as 

 the longitudinal one and is 

 the more regular in arrange- 

 ment. The thin longitudi- 

 nal layer is often imperfect, 

 especially along the attach- 

 ment of the mesentery. The 

 entire muscular coat dimin- 

 ishes in thickness towards 

 the lower end of the small 

 intestine. 



The serous coat, with 

 the exception of parts ot 

 the duodenum, completely 

 invests the gut except along 

 the line of attachment of the 

 mesentery, where the two 

 layers of peritoneum diverge, 

 leaving a non-serous area 

 between them for the passage of blood-vessels, lymphatics and nerves. 

 In structure the serous coat of the intestine corresponds to that of the 

 stomach, and includes essentially the fibro-elastic connective tissue stroma, 

 covered on the free surface with mesothelium. 



The blood-vessels supplying the small intestine reach the walls of the 

 tube between the peritoneal folds constituting the mesentery. After sending 

 branches to the serous coat, the arteries penetrate the muscular tunic (to the 

 outer part of which twigs are given in passing) to gain the submucosa. 

 Within the latter, additional twigs are given to the muscular coat, while 

 others supply the glands and lymph-nodules lying in this tunic. Larger 

 branches pass from the vessels of the submucosa into the mucous membrane, 

 some to break up into capillaries forming networks around the gland-tubules 

 and others to supply the villi. Each villus receives from one to three arteri- 

 oles, which resolve into capillaries occupying the peripheral part of the 

 stroma. The blood is returned by a single axial vein which traverses the 

 projection and becomes tributary to the larger venous stems within the sub- 

 mucous coat, as do the other veins of the tunica propria that commence near 



. 



FIG. 212. Transverse section of injected small intestine, show- 

 ing general distribution of vessels. X 45. 



