2 HAND-BOOK OF PHYSIOLOGY. 



Structure. The spleen is covered externally almost completely by 

 a serous coat derived from the peritoneum, while within this is the proper 

 fibrous coat or capsule of the organ. The latter, composed of connective 

 tissue, with a large preponderance of elastic fibres, and a certain propor- 

 tion of unstriated muscular tissue, forms the immediate investment of the 

 spleen. Prolonged from its inner surface are fibrous processes or trabeculce, 

 containing much unstriated muscle, which enter the interior of the organ, 

 and, dividing and anastomosing in all parts, form a kind of supporting 



FIG. 254. Section of dog's spleen injected: c, capsule; tr, trabeculae; m, two Malpighian bodies 

 with numerous small arteries and capillaries; a, artery; Z, lymphoid tissue, consisting of closely- 

 packed lymphoid cells supported by very delicate retiform tissue; a light space unoccupied by cells is 

 seen all round the trabeculae, which corresponds to the " lymph path 11 lymphatic glands. (Schofleld.) 



framework or stroma, in the interstices of which the proper substance of 

 the spleen (spleen-pulp) is contained (Fig. 254). At the hilus of the 

 spleen, the blood-vessels, nerves, and lymphatics enter, and the fibrous 

 coat is prolonged into the spleen-substance in the form of investing sheaths 

 for the arteries and veins, which sheaths again are continuous with the 

 trabeculce before referred to. 



The spleen-pulp, which is a dark red or reddish-brown color, is com- 

 posed chiefly of cells, imbedded in a matrix of fibres formed of the 

 branching of large flattened nucleated endotheloid cells. The spaces of 

 the network only partially occupied by cells form a freely communicating 



