CHAPTER XIV. 

 THE SPLEEN. 



Nearly the whole surface of the spleen is invested with a cov- 

 ering of peritoneum similar to that which partially covers the 

 liver. Beneath this is the true capsule of the spleen, which com- 

 pletely surrounds it. This capsule is composed of dense fibrous 

 tissue, containing a large number of elastic fibres and a few of 

 smooth muscular tissue. From its inner surface bands of the same 

 tissue, called the " trabecular," penetrate into the substance of the 

 organ, where they branch, and the branches join each other to form 

 a coarse meshwork occupied by the parenchyma of the organ, the 

 " pulp." 



The bloodvessels of the spleen enter at the hilum and pass into 

 the large trabecular, which start from the capsule at that point 

 and enclose the vessels until they divide into small branches. The 

 vessels then leave the trabecular and penetrate the pulp, where they 

 break up into capillaries, which do not anastomose with each other. 

 There is some doubt as to the way in which these capillaries end. 

 According to one view, they unite to form the venous radicles, so 

 that the blood is confined within vessels throughout its course in the 

 spleen. Another view is that the walls of the capillaries become 

 incomplete, clefts appearing between their endothelial cells, which 

 finally change their form and become similar to those of the reticu- 

 lum of the pulp. The veins, according to this view, arise in a 

 manner similar to the endings of the arteries. The result of this 

 would be that the blood is discharged, from the capillary termina- 

 tions of the arteries, directly into the meshes of the pulp, after which 

 it is taken up by the capillary origins of the veins (Figs. 159 and 160). 

 Studies of the vascular structures in the spleen made with the aid of 

 injections under varying conditions of pressure, in collapsed and in 

 distended spleens and with different injection-materials, have led to 

 a third view, which, if correct, would explain the divergent opinions 

 just mentioned. The delicate reticulum which pervades the organ is 

 elastic and forms a fine-meshed layer over the small vessels, support- 



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