SECRETION. 



319 



is of a deep red color, of a variable shape, generally oval, somewhat 

 concavo-convex. Vessels enter and leave the gland at the inner side or 

 hilus. 



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 framework or stroma, in the interstices of which the 

 proper substance of the spleen (spleen-pulp) is contained (fig. 228). 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 



Fie. 227. Section of injected dog's spleen: c, capsule: tr, trabeculse; m, two Malpighiaa 

 bodies with numerous small arteries and capillaries ; a, artery ; I, lymphoid tissue, consisting of 

 closely-packed lymphoid cells supported by very delicate retiform tissue ; a lightspace unoccupied 

 -Us is seen all round the trabeculae, which corresponds to the "lymph path" in lympiatic 



byc^l 

 glands. 



(Schofleld.) 



of investing sheaths for the arteries and veins, which sheaths again are 

 continuous with the trabecnlae before referred to. 



