

THE SPLEEN 



1285 



each containing numerous nuclei or one compound nucleus. Nucleated red-blood corpuscles 

 have also been found in the spleen of young animals. 



Bloodvessels of the Spleen. The lienal artery is remarkable for its large size in proportion 

 to the size of the organ, and also for its tortuous course. It divides into six or more branches, 

 which enter the hilum of the spleen and ramify throughout its substance (Fig. 1190), receiving 

 sheaths from an involution of the external fibrous tissue. Similar sheaths also invest the nerves 

 and veins. 



Each branch runs in the transverse axis of the organ, from within outward, diminishing in 

 size during its transit, and giving off in its passage smaller branches, some of which pass to the 

 anterior, others to the posterior part. These ultimately leave the trabecular sheaths, and ter- 

 minate in the proper substance of the spleen in small tufts or pencils of minute arterioles, which 

 open into the interstices of the reticulum formed by the branched sustentacular cells. Each of 

 the larger branches of the artery supplies chiefly that region of the organ in which the branch 

 ramifies, having no anastomosis with the majority of the other branches. 



The arterioles, supported by the minute trabeculse, traverse the pulp in all directions in bundles 

 (pencilli) of straight vessels. Their trabecular sheaths gradually undergo a transformation, 

 become much thickened, and converted into adenoid tissue; the bundles of connective tissue 

 becoming looser and their fibrils more delicate, and containing in their interstices an abundance 

 of lymph corpuscles (W. Miiller). 



Trabecula 



Lymphatic 

 nodule 



Spleen pulp 



Fio. 1191. Transverse section of a portion of the spleen. 



ie altered coat of the arterioles, consisting of adenoid tissue, presents here and there thick- 

 enings of a spheroidal shape, the lymphatic nodules (Malpighian bodies of the spleen). These 

 bodies vary in size from about 0.25 mm. to 1 mm. in diameter. They are merely local expansions 

 or hyperplasise of the adenoid tissue, of which the external coat of the smaller arteries of the spleen 

 is formed. They are most frequently found surrounding the arteriole, which thus seems to 

 tunnel them, but occasionally they grow from one side of the vessel only, and present the appear- 

 ance of a sessile bud growing from the arterial wall. In transverse sections, the artery, in the 

 majority of cases, is found in an eccentric position. These bodies are visible to the naked eye 

 on the surface of a fresh section of the organ, appearing as minute dots of a semiopaque whitish 

 color in the dark substance of the pulp. In minute structure they resemble the adenoid tissue 

 of lymph glands, consisting of a delicate reticulum, in the meshes of which lie ordinary lymphoid 

 cells (Fig. 1191). The reticulum is made up of extremely fine fibrils, and is comparatively open 

 in the center of the corpuscle, becoming closer at its periphery. The cells which it encloses 

 are possessed of ameboid movement. When treated with carmine they become deeply stained, 

 and can be easily distinguished from those of the pulp. 



The arterioles end by opening freely into the splenic pulp; their walls become much attenuated, 

 they lose their tubular character, and the endothelial cells become altered, presenting a branched 

 appearance, and acquiring processes which are directly connected with the processes of the 

 reticular cells of the pulp (Fig. 1192). In this manner the vessels end, and the blood flowing 

 through them finds its way into the interstices of the reticulated tissue of the splenic pulp. Thus 





