736 STRUCTURE OF 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 trabeculae 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 trabeculae, 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 trabeculee 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 trabeculse, 

 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 trabeculae 

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

 resemblance 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 anasto- 

 mosing tubular chambers; the trabeculse are closest towards the 

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

 arrangement of trabeculse, 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 corpuscles, 

 of which we will speak presently, the splenic reticulum is some- 

 what coarse, coarser than ordinary adenoid tissue (259), and over 

 a large part of the spleen is made up of branched nucleated cells, 



