138 NORMAL HISTOLOGY. 



vary greatly in different animals, being in man only 

 moderately developed. The nodules, or Malpighian 

 bodies, have essentially the same structure as the 

 nodules of the lymph-nodes that is, they are 

 formed by a small mass of supporting recticular 

 connective tissue, whose meshes are narrowest at the 

 periphery, and closely filled throughout with small 

 spheroidal cells, and supplied with a net-work of 

 capillaries ; we usually find here, however, a small 

 artery, passing either through the centre or at one 

 side of the nodule. 



But in order to fully understand the nodules of 

 the spleen, it is necessary to study their relation to 

 the arteries, in which respect they seem entirely to 

 differ from their analogues in the lymph-nodes. 

 The arteries and veins as they enter the hilus of the 

 spleen are surrounded, as above mentioned, by a 

 connective-tissue sheath ; after passing for a short 

 distance inward, they separate, and the arteries, still 

 accompanied by a certain amount of connective 

 tissue, divide and subdivide, proceeding farther in- 

 ward, until the small branches finally break up into 

 brush-like bundles of delicate twigs. If, now, we 

 carefully study the walls of the smaller arteries, we 

 find that in certain parts they undergo a singular 

 modification : at first the connective-tissue sheath 

 and the adventitia become very loose in texture, and 

 their meshes become filled with spheroidal cells re- 

 sembling lymph -cells this is called lymphoid infil- 



