334 THE ANATOMY OF THE HORSE. 



consist of two diftercnt kinds of tissue — the cortical and the medullary 

 substance of the kidney. 



The renal pelvis is a curved cavity, its extremities being termed the 

 arms. On its outer side there is a horizontal ridge — the renal a-est — 

 on which the uriniferous tubules open, and on its inner side it is con- 

 tinuous by a funnel-shaped opening with the lumen of the lu'eter. 



The cortical substance forms a layer beneath the capsule ; the medulla 

 is disposed around the pelvis and is internal to the cortical substance. 

 The cortex is about twice as thick as the medulla, but the two layers 

 meet along a sinuous line, and slightly intei-penetrate one another. It 

 will be noticed that the two layers contrast with one another in the 

 following respects : — The cortex is of a deep red colour, it is granular, 

 friable, and studded with numerous small shining points — the Malpigkian 

 bodies. The medulla, on the other hand, is pale red, striated, and 

 fibrous-looking, less friable than the cortex, and without any ^lalpighian 

 bodies. 



Uriniferous tvbules. — The largest tubes, or papillari/ ducts, open on the 

 crest of the pelvis. If such a tube be traced, it will be found to pass 

 oxitwards through the medulla, having a straight course, and branching 

 dichotomously. The smaller tubes resulting from this division are 

 called the collecting tubes ; and, still preserving their rectilinear course, 

 they enter the cortex in bundles termed the pi/ramids of Ferrein. At 

 the surface of these pyramidal bundles, the straight tubes curve out- 

 wards in the cortex, and become dilated and tortiious, forming the 

 intermediary or junctional tubules. Each of these is succeeded by a 

 narrow straight tubule, which descends from the cortex to the medulla, 

 where it forms a bend, or loop, and i-uns up again into the cortex. 

 There is thus formed the loojied tube of Henle, which is shaped like the 

 letter U. Having re-entered the cortex, Henle's tube becomes dilated 

 and tortuous, constituting the convoluted tube, which becomes constricted 

 and then expands into a bladder-like dilatation — Bowman's capsule. 

 Boivman's capside siuTounds a clue-like tuft of capillary vessels called 

 the glomerulus, and the whole constitutes a Malpighian body. It is 

 more natural, but less simple at first, to regard the tube as beginning 

 not at the crest of the pelvis, but at Bowman's capsule. The student 

 should mentally work it out in that direction for himself The urini- 

 ferous tubules consist of a basement membrane with an epithelial lining. 

 In the convoluted and intermediary tubes the cells are irregularly 

 columnar, but their outlines are obscure; in the descending limb of 

 Henle's tiibe (neai'est the capsule of Bowman) the cells are flattened ; 

 and elsewhere the cells lining the tubes are cubical or columnar. 



The Renal Vessels. The renal artery divides into a number of 

 branches which penetrate the kidney near the lulus. Reaching the 

 boundary line between the cortex and medulla, the artei'ies divide 



