518 PEYER'S PATCHES. [BOOK n. 



blood vessels and lymphatics are abundant. Over each follicle 

 both glands and villi are absent so that the upper surface of the 

 follicle is in contact with the epithelium of the intestine, which is 

 here shorter and more cubical than elsewhere. 



Each follicle consists of a somewhat spherical vascular mass 

 of adenoid tissue surrounded more or less completely by a lymph 

 sinus ; in fact the structure of each of these aggregated follicles 

 repeats so completely that of a solitary follicle that the same 

 description and discussion will serve for both. 



292. Lymphatic Glands. If the structure of a follicle just 

 described be borne in mind, that of a lymphatic gland is made 

 more easy; for, as a Peyer's patch is a mere aggregation of 

 otherwise unchanged follicles, so a lymphatic gland is a collection 

 of similar follicles differentiated into a compact and somewhat 

 complex organ. 



A typical lymphatic gland has, though the form varies a good 

 deal, the shape of a kidney, in so far at all events that a more or 

 less convex side can be distinguished from a concave side in which 

 is placed the hilus where the blood vessels enter and issue ; from 

 the hilus also issue lymphatic vessels, which since they carry 

 lymph away from the gland are called efferent lymphatics. The 

 afferent vessels carrying lymph to the gland pass into the gland in 

 a scattered fashion on the convex side. 



The gland is invested by a capsule of connective tissue, 

 containing in the case of many animals a very considerable 

 number of plain muscular fibres. Two layers may at times be 

 distinguished in the capsule : an outer layer of coarser and an 

 inner layer of finer connective tissue, a rich plexus of lymphatic 

 vessels being placed between the two. From the capsule a 

 number of partitions or trabeculce, starting from various points of 

 the surface and consisting, like the capsule, of closely interwoven 

 bundles of connective tissue mixed up with a variable number of 

 plain muscular fibres, pass into the gland in a direction converging 

 towards the hilus. In the outer or circumferential part of the 

 gland these trabeculse are large, run in a straight direction, are 

 but little branched, and are so arranged that they cut up the 

 outer part of the gland into a number of chambers, having more 

 or less the form of truncated pyramids, converging to or radiating 

 from the inner portion of the gland near the hilus. These 

 chambers have been called alveoli, and constitute together the 

 cortex of the gland, the inner portion being called the medulla. 

 On reaching the medulla the trabeculse, the course of which as we 

 have just said is in the cortex on the whole straight and unbranched, 

 rapidly divide becoming thinner and more slender and, running 

 and joining together in all directions, form an irregular open 

 network giving rise to a labyrinth of passages into which the 

 alveoli of the cortex open. 



The trabeculae in fact starting from the capsule divide the 



