1784 



HUMAN ANATOMY. 



pigments, when injected into the arteries, pass into the veins. The walls of the 

 ampullse are very thin and, towards the junction with the venous radicles, imper- 

 fect, being here composed of the reticulum of the surrounding pulp-tissue. The 

 channels, however, are sufficiently definite to prevent the escape of the blood-cells 

 under normal conditions, although the plasma constantly passes into the intercellular 

 spaces of the pulp (Mall). The walls of the venous spaces are even more pervious 

 than those of the ampulke, and, like the latter, possess only an incomplete endothelial 

 lining, supported externally by a mesh of circularly disposed elastic fibres. The endo- 

 thelium consists of narrow, elongated spindle-cells instead of the usual plate-like ele- 

 ments which line the larger splenic blood-vessels. The round or oval nuclei project 

 into the lumen of the venous space beyond the level of the protoplasm of the cell, which 

 often presents a distinct striation. 



The venous spaces between the pulp-cords are the beginnings of more definite 

 channels, the intralobular veins, which pass from the primary compartments towards 



Fig. I 506. 



Primary compartment 



Venous space 



Intralobular vein 



Interlobular trabecula  



Intralobular trabecula 



Interlobular vein 



Malpighian body 



Capsule 



Venous space 



nterlobular vein 



Splenic artery 



Diagram showing architecture of splenic unit ; splenic pulp is represented in only one compartment. {After Malt.) 



the trabeculae between the lobules to become tributaries of the larger interlobular 

 veins occupying the periphery of the lobules within the boundary septa. These veins 

 follow the larger trabeculae until, finally, they emerge at the hilum to form the splenic 

 vein. 



In their journey through the lobule, shortly after leaving the trabeculae, the 

 branches of the splenic artery present marked local accumulations of lymphoid tissue 

 within their adventitia. These aggregations constitute the Malpighian bodies, or 

 spleriic nodules. When seen in transverse section, they appear as conspicuous oval 

 areas of dense lymph-tissue surrounding the artery, which usually occupies a somewhat 

 eccentric position. Longitudinally sectioned, the splenic nodules appear as cylinders. 

 They correspond in structure with true lymph-nodes, possessing germ-centres. Sur- 

 rounding the Malpighian bodies, the spleen-tissue presents the usual arrangement of 

 Jhe pulp-cords. 



The splenic pulp consists of a delicate supporting reticulum, continuous with 

 the terminal ramifications of the intralobular trabeculae, and the cells contained within 



