170 SIXTEENTH LECTURE. 



A variety of views prevail, however, concerning the vascular 

 relations of the medulla. Elongated vascular tufts, which 

 appear in the upper portion of the medullary substance, the 

 so-called boundary layer (Fig. 150,/), are called vasa recta 

 (Fig. 151, f\ 155, k and /). They pass, sometimes further 

 upwards, sometimes further downwards, in a looped or 

 noose-like manner, into each other, and may be mistaken 

 for the looped canals of the urinary passages (Fig. 151, e). 

 Our vasa recta then form an elegant net-work (Fig. 155, m) 

 around the apertures of the uriniferous canals at the apex of 

 the medullary pyramids. 



These vasa recta have frequently, if not predominantly, a 

 venous character (/) ; they are continuations of the capillary 

 net-work of the cortical pyramids. 



Then — and we regard this source of supply as the more 

 important — the medullary vessels arise from the breaking 

 up of the vasa efferentia of the deepest glomeruli (Fig. 



155,0- 



Quite isolated arterial branches, which have left the coil- 

 bearing arteries before the giving off of the glomerulus 

 branches, are, according to our views, of little consequence, 

 though many investigators have considered these so-called 

 arteriolae rectae to be of great importance. 



The combination of the vasa recta into venous roots (/) 

 presents a similar condition. They frequently have a tuft- 

 like character. Their affluent tubes are the returning sides 

 of the looped vessels and the effluent canals of the papillary 

 apices. These venous roots empty in part into the lower 

 terminal portion of the cortical veins, in part into the arched 

 communications at the margin between the cortex and the 

 medulla. 



We are familiar with the lymphatics of the dog's kidney 

 (Ludwig and Zawarykin). They occupy the interstices of a 

 connective tissue full of clefts, which is situated beneath the 

 capsule, and from here are in communication with the capsu- 

 lar passages, and then form in the cortical pyramids finer, 

 deeper canals between the uriniferous canals, capsules of the 



