DISSECTION OF THE ABDOMEN. 345 



is connected only by delicate processes and vessels. If a horizontal 

 section be made from the convex border to the hilus of the kidney, 

 the organ will be seen to possess a cavity towards the hilus, termed 

 the pelvis, and to consist of three strata of substance — the cortex, 

 the boundary layer, and the medulla 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 crest — on 

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

 by a funnel-shaped opening with the lumen of the ureter. 



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

 is disposed around the pelvis, and the boundary layer is interposed 

 between these two. The cortex is the thickest, and the boundary layer 

 the thinnest, of the three strata. It will be noticed that the three 

 layers contrast with one another in the following respects : The cortex 

 comprises the labyrinth, and the medullary rays or pyramids of Ferrein. 

 The labyrinth forms the dark-red ground-work of the cortex, and it 

 contains the malpighian bodies, which may be just visible to the naked 

 eye as darker points. From the boundary layer it is penetrated by the 

 series of medullary rays, which are lighter in colour than the labyrinth. 

 On the cut surface each ray presents itself as a tapering streak, of which 

 the base is continuous with one of the light stripes of the boundary 

 layer, and the point is lost to sight near the surface of the cortex. 



The medulla is pale red, striated, and fibrous-looking, less friable than 

 the cortex, and without any malpighian bodies. The intermediate 

 boundary layer is somewhat similar in appearance to the medulla ; but, 

 especially in a congested kidney, it shows alternate radial light and 

 dark stripes, the former being bundles of straight uriniferous tubes, and 

 the latter bundles of vessels. 



Uriniferous Tubides. — The largest tubes, or papillary ducts, open on the 

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

 outwards 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 pass through the boundary layer (of which they form the light 

 stripes), and enter the cortex in bundles as the medullary rays or 

 pyramids of Ferrein. At the surface of these pyramidal bundles, the 

 straight tubes curve outwards in the cortex, and become dilated and 

 tortuous, 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 runs up 

 again into the cortex. There is thus formed the looped 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 



