XX.] 



THE SPLEEN. 



243 



In the guinea-pig the lymphoid mass lorms almost a continuous 

 covering. 



The Malpighian corpuscles occur chiefly at the bifurcations of 

 the artery, so that the artery perforates them usually at one side, 

 and thus the mass is arranged in a lob-sided manner on the artery. 

 In structure they resemble the follicular substance of lymphatic 

 glands, and in the centre of some of them is a lymph-knot, in which 

 mitosis occurs. 



The splenic pulp consists of a mesh-work composed of branched 

 cells with membranous expan- 

 sions, and the processes of Ca gule 

 neighbouring cells anastomose 

 to form a fine reticulum, which 

 occupies the irregular chambers 

 of the trabecular framework, Trabeculw. 

 and with which it is continu- 

 ous. The meshes of this fine 

 network are occupied by cellu- 

 lar elements in considerable 

 variety. This reticulum is per- 

 meated by blood-corpuscles in 

 fact, the blood stream of the 

 spleen seems to bear the same 

 relation to this reticulum that 

 the lymph stream bears to a Pulp - 

 lymph gland. Besides red 

 blood - corpuscles there are 

 larger cells called splenic cells ; Trabecula. 

 some of these often contain 

 degenerated blood-corpuscles or 

 pigment. There are also leuco- Artei r- 

 cytes (fig. 232). The arteries 

 enter the spleen at the hilum, 

 and run for a short part of 

 their course in the trabeculse, 

 which they soon leave, enter the reticulum, and break up into 

 pencils or groups of small arteries. Some of these open into true 

 capillaries in the Malpighian corpuscles; other fine branches open 

 directly into the reticulum. The endothelial lining, instead of 

 forming a continuous membrane, leaves apertures between the cells, 

 through which the blood escapes. The veins arise from the spaces 

 of the reticulum, and rapidly pass into the trabecula?, in which they 

 are firmly fixed. Near the hilum, and for part of their course, the 

 arteries and veins lie in a " common sheath," with the corresponding 

 nerves. The vein is always much wider than the corresponding 



FIG. 231. T.S. Part of the Human Spleen. 

 M tiller's fluid, haeniatoxylin, x 10. 



