122 



NORMAL HISTOLOGY. 



The trabeculae all along their course give off numerous ramifi- 

 cations ; each of these breaks up into still finer bands, until the final 

 divisions of the fibrous tissue terminate in the delicate reticulum con- 

 stituting the supporting framework in whose meshes the lymphoid 

 cells are held. In the areas of denser tissue the cells are so closely 

 placed that the supporting reticulum is almost completely masked. 

 The surfaces of the fibrous bundles and partitions, especially those 

 directed towards the lymph-sinuses, support numerous plate- like 

 connective-tissue cells, in places these elements constituting 

 almost an endothelial covering. 



The blood-vessels supplying the lymphatic glands are arranged 

 as two groups : the one set gains entrance at the periphery and is 

 distributed principally to the capsule and larger trabeculae ; the other 

 group enters at the hilum, the majority of the arterial branches pass- 

 ing directly into the lymphoid 'tissue, while a few follow the course of 

 the larger septa ; these, following the latter course, give off numerous 

 twigs to the surrounding adenoid tissue, the terminal branches con- 

 tinuing to the capsule, where they finally are distributed. The cap- 

 illaries derived from the breaking up of the arterial twigs entering at 

 the hilum especially ramify through the denser adenoid tissue, avoid- 

 ing the loosely reticulated lymph-sinuses. The distribution of the 

 nerves passing to the compound lymphatic glands is uncertain, the 

 supply including bundles of both the medullated and the pale fibres. 



In addition to the numerous well-developed compound lymphatic 

 follicles, many of which, as the mesenteric and the bronchial glands, 

 reach conspicuous dimensions, certain organs present special modifi- 

 cations of adenoid tissue ; such are the spleen and the fully-developed 

 thymus body, which therefore may be included with propriety in the 

 account of the lymphatic structures. 



THE SPLEEN. 



The spleen may be regarded as a specialized compound lymphatic 

 gland, modified by the arrangement of its blood-supply. The organ 

 is invested by a firm capsule, composed of a dense felt- work of 

 bundles of fibrous tissue, with which are mixed numerous elastic 

 fibres. The outer surface of the capsule, with the exception of a 

 limited area, is covered by the serous coat of the peritoneum, the 

 union between the two being very intimate. 



On the inner surface the capsule is continuous with numerous 

 prolongations, the trabeculae. These penetrate deeply into the 

 interior from all sides, and by the free union of their processes form 

 a spongy connective-tissue framework throughout the organ, 

 enclosing an elaborate system of intercommunicating spaces occupied 

 by the lymphoid tissue. 



