THE SPLEEN 



165 



Mall* has shown that each terminal artery enters a lobular 

 compartment which is partially outlined by coarser trabeculae, and 

 within which is a mass of spleen pulp supported by the finer tra- 

 becular processes and the still more delicate reticulum. This 

 schematic structural unit he has termed the lobule of the spleen. 

 The terminal artery enters its axis through that margin which is 

 directed toward the hilum. Within the lobule the artery gives off 

 its terminal twigs, which end in minute dilatations, the ampullce 

 of Thoma. From some of these end twigs, capillary spaces direct 

 the blood current into the broad venous radicals. Elsewhere the 

 blood seems to be poured directly into wide pulp channels, com- 

 parable to the sinuses of the lymphatic glands, by which the 

 blood current under ordinary conditions is directed into the 

 venules, but which under conditions of very slightly increased 

 blood pressure permit the extravasation of considerable quantities 

 of blood into the meshes of the surrounding splenic reticulum. 



The veins begin as wide sinusoidal channels within the splenic 

 pulp. At first, and for a considerable distance, they follow an 

 independent course through 

 the pulp, receiving at the 

 same time frequent acces- 

 sions of blood from other ve- 

 nous radicals. Finally, how- 

 ever, the veins enter the 

 larger trabeculse, but are still 

 devoid of more complete 

 coats than the thin mem- 

 brane of fibro-elastic tissue 

 which surrounds the endo- 

 thelial tube, but which is 

 now ensheathed by the tra- 

 becular tissue. Henceforth 

 the path of the veins lies 

 within the trabeculae, and is 

 directed toward the hilum. On approaching the hilum the larger 

 veins acquire the usual venous coats. Having arrived at the hilum 

 they form several efferent vessels which, in the outlying connective 

 tissue, form by their union the splenic vein. 



The spleen is poorly supplied with lymphatics. These vessels 



FIG. 161. THE ORIGIN OF A VEIN IN THE 



SPLENIC PULP. 



a, venous endothelium ; 6, leucocytes ; c, 

 red blood cells (appearing rather too dark in 

 the reproduction) ; d, a mesh of the splenic 

 pulp. Highly magnified. (After Bannwarth.) 



* Johns Hop. IIosp. Bull., 1898. 



