738 STRUCTURE OF SPLEEN. [BOOK n. 



with the labyrinth of the splenic reticulum ; and by a converse 

 process the same labyrinth is made continuous with the plexiform 

 beginnings of small veins, the so-called venous sinuses, which end 

 in the veins running along the trabeculae. 



Thus the blood flowing along the splenic artery escapes from 

 the open ends of the minute arteries into the splenic reticulum, 

 and is gathered up from the reticulum into the open mouths of 

 minute veins. When the capsule and trabeculse are in a relaxed 

 condition a not inconsiderable portion of blood thus escapes into 

 the reticulum and tarries in the meshes where it undergoes 

 changes of which we shall presently speak : when the capsule and 

 trabeculse are contracted and shrunken, the blood flows in a 

 more direct manner through the narrowed channels from the 

 arteries into the veins. 



472. The lymphatic vessels of the spleen are not very 

 numerous. The capsule and the trabeculse contain lymphatic 

 plexuses opening into lymphatic trunks, which leave the hilus with 

 the blood vessels. There is, however, a remarkable lymphatic 

 development, in the form of a sheath of adenoid tissue, which 

 accompanies the arteries for some distance as they leave the 

 trabeculse and with which the lymphatic vessels of the trabeculse 

 are connected. So long as the arteries are running along the 

 trabeculse this adenoid sheath is either absent or extremely scanty ; 

 but as the finer arterial branches plunge into the reticulum, it is 

 so increased in bulk at intervals, and especially where an artery 

 is dividing into two, as to form an oval or spherical mass visible 

 to the naked eye, and conspicuous from its colour because the 

 adenoid tissue, crowded as usual with leucocytes, appears white or 

 colourless as compared with the dark red spleen pulp. These, in 

 fact, are the Malpighian corpuscles spoken of above. Each 

 Malpighian corpuscle is a more or less globular mass of adenoid 

 tissue, crowded with leucocytes, developed in the adventitia of 

 a minute artery running in the splenic reticulum. As a rule 

 the development takes place on one side of the artery, so that 

 the rounded Malpighian corpuscle seems to be sitting on the 

 artery. Sometimes the development takes place more or less 

 regularly on all sides of the artery, so that the artery appears to 

 pierce and run through the rounded mass, which is then called 

 not a Malpighian corpuscle but a " hyperplasic spot " ; and not 

 infrequently the artery divides in the middle of the mass. 



^The adenoid tissue, as elsewhere ( 259), is composed of a fine 

 reticulum crowded with leucocytes; the corpuscle in fact closely 

 resembles a solitary gland of the intestine or a rounded mass of 

 the follicular substance of a lymphatic gland. But it differs from 

 these structures in not being surrounded by any distinct lymph- 

 sinus ; at the circumference the true adenoid tissue passes suddenly 

 into the coarser splenic reticulum. The artery as it passes through 

 the Malpighian corpuscle gives off to it fine branches which form a 



