CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 737 



the branches of which are membranous and flange-like rather than 

 filamentous. These flanges of neighbouring cells join with each 

 other, and thus form a labyrinthine network, the walls of the minute 

 passages of which are formed not of fibres but of irregular sheets. 

 In son ic parts of the spleen, however, these flange-like processes are 

 replaced by fibres, and, the bodies and nuclei of the constituent 

 cells being rare, the reticulum appears as a more ordinary 

 reticulum of fine fibres. 



The bars of this reticulum, whether flange-like or filamentous, 

 are at the edges of the trabeculae continuous with the substance of 

 the trabeculae ; the smaller trabeculas break up into the reticulum, 

 and the larger trabeculae are fringed with processes continuous 

 with the bars of the reticulum. Thus the coarser network of the 

 trabecular system is continuous with the finer network of the 

 reticulum. 



The reticulum of the lymphatic gland contained, it will be 

 remembered, besides fluid, leucocytes, these being crowded in 

 the follicle and more sparse in the lymph sinus. The splenic 

 reticulum also contains leucocytes, but these are thrown into 

 the background by the large number of red corpuscles with 

 which the meshes of the reticulum are crowded. The reticulum \ 

 in fact is filled with blood ; and peculiar arrangements exist by \ 

 which the blood gains access to the spaces of the reticulum. What 

 we spoke of above as 'spleen pulp' expressed from the fresh spleen 

 consists of fragments of the reticulum together with the red and 

 white corpuscles occupying the meshes of that reticulum. 



471. The splenic arteries entering the spleen at the hilus 

 are in some animals at first supported by the trabeculas, along 

 which they run dividing as they go, but the branches at last leave 

 the trabeculae and plunge into the reticulum. In other animals 

 the arteries run more independent of the trabecula?. As they leave 

 the trabeculaB, or to.wards their terminations, the small arteries are 

 apt to divide into pencils of small twigs. In a similar manner 

 the veins may be traced back along the trabeculse, small and 

 great, along which they are gathered up from smaller veins 

 of the reticulum ; but the veins do not run in the reticulum 

 as distinct vessels to the same extent that the arteries do. 



In the reticulum the minute arteries, according to most 

 observers, are not continuous in the usual manner with veins by 

 means of closed capillaries; but a peculiar arrangement is met 

 with. The epithelioid plates forming the capillary wall, instead 

 of being cemented together to form a continuous tubular sheath, 

 are separate from each other, come asunder as it were, and thus 

 allow the lumen of the capillary or rather of the minute artery to 

 open out into the splenic reticulum ; indeed the epithelioid plates 

 no longer retain their simple spindle shape, but becoming branched - 

 and irregular are transformed into the cells of the reticulum. 

 In this way the channel of the blood vessel becomes continuous 



F. 47 



