JCHNOLOG] 



the blood passing through the spleen is brought into intimate relation with the elements of tht: 

 pulp, and no doubt undergoes important changes. 



After these changes have taken place the blood is collected from the interstices of the tissue 

 by the rootlets of the veins, which begin much in the same way as the arteries end. The con- 

 nective-tissue corpuscles of the pulp arrange themselves in rows, in such a way as to form ar 

 elongated space or sinus. They become elongated and spindle-shaped, and overlap each other 

 at their extremities, and thus form a sort of endothelial lining of the path or sinus, which is the 

 radicle of a vein. On the outer surfaces of these cells are seen delicate transverse lines or markings, 

 which are due to minute elastic fibrilla3 arranged in a circular manner around the sinus. Thus 

 the channel obtains an external investment, and gradually becomes converted into a small 



Branching cell 



Small 

 artery 



Vessel continuous 

 with processes of 

 network cells 



Branching cell 





FIG. 1192. Section of the spleen, showing the termination of the small bloodvessels. 



vein, which after a short course acquires a coat of ordinary connective tissue, lined by a layer of 

 flattened epithelial cells which are continuous with the supporting cells of the pulp. The smaller 

 veins unite to form larger ones; these do not accompany the arteries, but soon enter the tra- 

 becular sheaths of the capsule, and by their junction form six or more branches, which emerge 

 from the hilum, and, uniting, constitute the lienal vein, the largest radicle of the portal vein. 



The veins are remarkable for their numerous anastomoses, while the arteries hardly anastomose 

 at all. 



The lymphatics are described on page 711. 



The nerves are derived from the celiac plexus and are chiefly non-medullated. They are 

 distributed to the bloodvessels and to the smooth muscle of the capsule and trabeculse. 



