The blood is collected from the interstices of the splenic tissue by the rootlets of the veins, which begin much in the same way as the arteries end.

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 fibrils arranged in a circular manner around the sinus.

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

This article incorporates text in the public domain from page 1286 of the 20th edition of Gray's Anatomy (1918)