952 



THE ORGANS OF DIGESTION. 



by a delicate reticulum of branched connective-tissue corpuscles the interstices of 

 which are occupied by blood, and in which the blood-vessels terminate in the 

 manner now to be described. 



Blood-vessels of the Spleen. The splenic 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. 524), receiving sheaths from the 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 terminate 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 trabeculae, traverse the pulp in 

 all directions in bundles or penicilli of straight vessels. Their external coat, on 

 leaving the trabecular sheaths, consists of ordinary connective tissue, but it gradu- 

 ally undergoes a transformation, becomes much thickened, and is converted into 

 a lymphoid material. 1 This change is effected by the conversion of the con- 

 nective tissue into a lymphoid tissue, the bundles of connective tissue becoming 

 looser and laxer, their fibrils more delicate, and containing in their interstices 

 an abundance of lymph-corpuscles (W. Mttller). This lymphoid material is 

 supplied with blood by minute vessels derived from the artery with which they 

 are in contact, and which terminates by breaking up into a network of capillary 

 vessels. 



The altered coat of the arterioles, consisting of lymphoid tissue, presents here 

 and there thickenings of a spheroidal shape, the Malpighian bodies of the spleen. 

 These bodies vary in size from about the yj-g- of an inch to the -^ of an inch in 

 diameter. They are merely local expansions or hyperplasise of the lymphoid 

 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 

 appearance of a sessile bud growing from the 

 arterial wall. Klein, however, denies this, and 

 says it is incorrect to describe the Malpighian 

 bodies as isolated masses of adenoid tissue, but 

 that they are always formed around an artery, 

 though there is generally a greater amount on 

 one side than the other, and that, therefore, 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 semi-opaque whitish color in the 

 dark substance of the pulp. In minute structure 

 they resemble the adenoid tissue of lymphatic 

 glands, consisting of a delicate reticulum in the 

 meshes of which lie ordinary lymphoid cells. 

 The reticulum of the tissue is made up of extremely delicate fibrils, and is 

 comparatively open in the centre of the corpuscle, becoming closer at the periphery 



1 According to Klein, it is the sheath of the small vessel which undergoes this transformation, 

 and forms a " solid muss of adenoid tissue which surrounds the vessel like a cylindrical sheath " (Atlas 

 tf Histology, p. 424). 



!o. Part of a Malpighian capsule 

 of the spleen of man. (Klein and Noble 

 Smith.) , Arterial branch in longitudinal 

 section, b. Adenoid tissue, still containing 

 the lymph-corpuscles ; only their nuclei 

 are shown, c, Adenoid reticulum, the 

 lymph-corpuscles accidentally removed. 



