772 STRUCTURE OF THE SPLEEN. [BOOK n. 



splenic artery with the splenic nerves enter, and whence the 

 splenic veins issue. The mode of branching is irregular, and the 

 branches vary in size, larger trabeculaB giving rise to smaller ones, 

 so that the whole interior of the organ is divided into a labyrinth 

 of irregular communicating chambers, which contain in the fresh 

 state the spleen-pulp mentioned above. 



The basis of both capsule and trabeculse, small and great, is 

 connective tissue well furnished with elastic elements. In some 

 animals, as for instance in the dog, this basis is so richly provided 

 with plain muscular fibres, that both trabeculae and capsule (in its 

 deeper layers) seem to be almost entirely composed of muscular 

 tissue. In other animals, in man for instance, the muscular 

 elements are much more scanty. The capsule and trabeculaB, 

 small and great, thus form a sponge-like framework, which being 

 elastic can, even in the cases where the muscular fibres are scanty 

 or absent, at one moment be distended so that the chambers are 

 capacious, and at another moment can by virtue of its elasticity 

 shrink so that the chambers are reduced in size. In the animals 

 in which muscular fibres are abundant still greater variations of 

 size are possible. When the muscles are relaxed, a distending 

 force, such as is furnished by the pressure of the blood-stream, 

 can swell out the framework to a very great bulk ; and an 

 adequate contraction of the muscular fibres can in turn squeeze 

 the sponge-like mass into very small dimensions. As we shall 

 presently see, rhythmical or other contractions of the capsule and 

 trabecular labyrinth, in animals in which these are largely muscular, 

 do produce remarkable and important variations in the volume of 

 the spleen. 



470. This sponge-like framework of capsule and trabeculse 

 reminds one of the structure of a lymphatic gland, and the re- 

 semblance is carried still further by the chambers of the labyrinth 

 being occupied by a reticular modification of connective tissue. 

 But the resemblance is superficial only. The chambers marked 

 out by the trabeculse of the spleen are wholly irregular ; there is 

 not, as in a lymphatic gland, any distinction between a cortex 

 with large radiating chambers and a medulla with anastomosing 

 tubular chambers; the trabecula? are closest towards the hilus, 

 but otherwise one part of the spleen, as regards the arrangement 

 of trabecula?, is like any other. Moreover the reticular tissue 

 occupying the chambers shews no distinction between lymph-sinus 

 and follicle, is not exactly like the fine reticulum of the one or the 

 coarse reticulum of the other, but of a nature distinct from each, 

 and has no special connection with lymphatics, but has peculiar 

 relations to the minute blood vessels. 



Except at the white spots occupied by the Malpighian cor- 

 puscles, of which we will speak presently, the splenic reticulum is 

 somewhat coarse, coarser than ordinary adenoid tissue ( 259), and 

 over a large part of the spleen is made up of branched nucleated 



