CHAP. XXXIV.] MATRIX. 485 



animals, it is also conspicuous. In the ox, the division into lobes 

 extends only to the pyramids. 



Parenchyma. The parenchyma of the kidney consists of two 

 distinct portions ; the one cortical, about half an inch in thickness, 

 forming the whole convex surface of the organ, of a dark red 

 colour, and to the unaided eye of a granular appearance, and 

 exhibiting numerous red spots (Malpighian bodies) abundantly 

 scattered through it. The medullary portion is embraced in 

 this ; it is pale and smooth, arranged so as to form several pyra- 

 mids, varying in number from eight to fifteen; their bases are 

 placed towards the cortex, from which may be traced a number 

 of nearly straight lines, which converge towards the summit of 

 the pyramid to which they belong. In this part of the kidney 

 there are no Malpighian tufts, and even to the unaided eye, it ap- 

 pears to be composed of a number of straight converging lines or 

 tubes. 



These pyramids or cones end by free summits which project on 

 the hilum into the pelvis of the kidney, the mucous membrane 

 lining this cavity being continuous at the summit of the cone (or 

 mamilla) with the tubes. The mucous membrane of the pelvis, 

 however, forms a sort of fossa, or saucer-shaped cavity, around each 

 mamilla, or termination of the pyramid. These calyces receive 

 the urine escaping from the open orifices of the tubes on the sum- 

 mit of the cones, and convey it toward the pelvis; they become 

 enormously increased in dimensions if there be any obstruction 

 to the passage of the urine from the ureter or bladder. 



Matrix. With reference to the presence of a fibro- cellular 

 matrix in the kidney, which serves as a support for the vessels and 

 tubes, there has been much difference of opinion. It was originally 

 described by Goodsir, and has since been noticed by several 

 observers. 



The matrix appears to us to be composed of a firm transparent 

 and granular substance, in which we have seen small granular cells ; 

 but have not been able to ascertain their precise nature. The 

 fibrous appearance seen in thin sections, we believe to be due 

 rather to the crumpled state of the walls of the capillaries and 

 uriniferous tubes, than to the existence of ordinary fibrous tissue 

 in the matrix itself. 



The intervals between the contiguous tubes and capillaries are 

 greater in the pyramids than in the cortical portion of the organ, 

 and consequently the matrix is more distinct in this situation ; but 



