350 EPITHELIAL AND ENDOTHELIAL TISSUE. 



varying amount of a brown, granular pigment. The myxoma- 

 tous reticulum in the medullary portion contains in its meshes 

 lymph-corpuscles varying greatly in size. Both in the medulla 

 and the connective-tissue capsule there are numerous ganglionic 

 nerve elements (Von Brunn) which are in connection with the 

 sympathetic nerve, branches of which, in large number, penetrate 

 the suprarenal capsule. This organ has likewise a large supply 

 of blood-vessels. Its development and functions are still physi- 

 ological puzzles. 



The spleen, in its structure, is closely allied to the lymph-gan- 

 glia, though its relation to the lymphatic system is by no means 

 clear. Like the lymph-ganglia, the spleen has also a connective- 

 tissue capsule sending numerous offshoots into the depths of the 

 organ, where it produces a delicate myxomatous reticulum. The 

 meshes of this reticulum contain a comparatively small amount 

 of lymph-corpuscles, while these form larger globular heaps, sim- 

 ilar to the follicles of the lymph-ganglia, the so-called Malpigh- 

 ian corpuscles, and elongated tracts, similar to the follicular 

 cords the so-called pulp-cords. The connective-tissue capsule 

 has for its outer investment the endothelia of the peritoneum ; 

 in many mammals it contains a large number of bundles of 

 smooth muscles, which also pervade the mass of the spleen. In 

 man, the number of fibers of smooth muscle in this organ varies 

 greatly, although small bundles are unquestionably found in many 

 cases. The connective-tissue septa of the spleen are in union 

 with the outer capsule, and produce branching and anastomos- 

 ing trabeculae throughout the pulp. These trabeculae carry the 

 arteries and veins, both of which enter or leave the spleen at dif- 

 ferent points, usually far apart. 



The arterioles in most mammals show a distinct adventitial 

 coat, which is crowded in its whole extent with lymph-cor- 

 puscles, so much so that each pulp-cord is pierced in its center 

 by an arteriole. In man, the lymph-corpuscles around the arter- 

 iole are accumulated in lymph-follicles, varying in size, and either 

 uniformly surrounding the vessel or attached more or less eccen- 

 trically to one side of the vessel. A favorite seat of these so- 

 called Malpighian corpuscles is the point of ramification of the 

 arteriole. In mammals' spleens which abound in muscles, f. i., 

 in the badger's spleen, we observe bundles of smooth muscle- 

 fibers accompanying the artery and surrounding the follicle, 

 which is in connection with the layer of lymph-corpuscles in the 

 adventitia of the artery. (See Fig. 148.) 



