530 PHYSIOLOGY CHAP. 



traversing the follicles, yields up some materials and acquires 

 others. 



The so-called Peyer's Patches, of an oblong oval form, which 

 are found to the number of 20-30 in the small intestine (particu- 

 larly in the ileum), consist of groups of the solitary follicles, so 

 that they are also termed agminated follicles. Each patch in man 

 consists of 50-100 follicles, arranged in one plane, which lie 

 immediately beneath the intestinal epithelium, and dip down so 

 far into the submucosa that they interrupt the muscular layer. 

 From the physiological standpoint they differ in no essential from 

 the solitary follicles. 



A more complex structure attaches to the lymphatic glands, 

 numerous and widely distributed bodies which lie along the 



FIG. 249. Vertical section of dog's lymphatic gland, the afferent lymphatics injected with Prussian 

 blue, stained with picrocarmine. (Klein.) c, Capsule, showing a lymph vessel cut trans- 

 versely, communicating with cortical sinuses ; a, lymph follicles of cortex surrounded by lymph 

 sinuses, and separated by trabeculae ; b, medullary portion of gland, showing' reticular 

 adenoid tissue and lymphatic sinuses injected with blue. Magnification of 25 diameters. 



course of the lymphatic vessels. They differ in size, and are for 

 the most part bean-shaped or kidney- shaped, with a concavity 

 which is called the hilum of the lymphatic gland, whence issue 

 the efferent lymphatics, while the afferent vessels enter on the 

 convex side. The arterial and venous blood - vessels enter and 

 leave respectively at the hilum. Each ganglion is invested with 

 a capsule composed of two layers, the outer of which consists of 

 loose connective tissue, and the interior of more compact connective 

 tissue with numerous smooth muscle cells. From this internal 

 capsular layer septa, or trabeculae, of the same connective and 

 muscular character as the capsule, run out, and pass to the hilum, 

 where they divide the cortical part of the gland into various com- 

 partments known as alveoli. On joining the internal or medullary 

 part of the gland the trabecular tissue divides into finer 

 strands interconnecting in every direction, and forming an open 



