PHYSIOLOGICAL ANATOMY OF THE KIDNEYS. 399 



Malpighian Bodies. These are ovoid or rounded terminal dilatations of the convo- 

 luted tubes, of somewhat variable size, measuring from ^ to T -i-g- of an inch in diam- 

 eter. They are composed of a membrane continuous with the external membrane of 

 the convoluted tubes, of the same homogeneous character, but somewhat thicker, meas- 

 uring about ^oio-o of an mcn > while the membrane of the tubes is only about 40 ^ 00 - of an 

 inch in thickness. This sac, which is sometimes called the capsule of Muller, encloses a 

 mass of convoluted blood-vessels and is lined with a layer of nucleated epithelial cells. 

 In addition to these pale, delicate cells lining the capsule, there are other cells which are 

 applied to the blood-vessels. These latter cells are probably concerned in the elimina- 

 tion of the solid constituents of the urine. 



The cells attached to the capsule of Muller are smaller and more transparent than 

 those lining the convoluted tubes. They are ovoid, nucleated, and finely granular. The 

 cells covering the vessels, however, are larger and more opaque, and they resemble the 

 epithelium lining the tubes. They measure from y^ 1 -^ to T Vo f an mc ^ m diameter, by 

 about -g-jVo- of an inch in thickness. 



Tubes of the Cortical Substance. Following out the tubes in the cortical substance 

 from the Malpighian bodies, we find first a short, constricted portion, which is some- 

 times called the neck of the capsule. The tube soon dilates to the diameter of about 

 TTO f an inch, when its course becomes exceedingly intricate and convoluted. These 

 are what are known as the convoluted tubes of the kidney. The membrane of these 

 tubes is transparent and homogeneous, but quite firm and resisting. It measures about 

 4(^60 of an m h in thickness. It is lined throughout with a single layer of rounded 

 or irregularly polygonal epithelial cells, from y^Vfr to ygVg- of an inch in diameter, some- 

 what larger, consequently, than the cells lining the straight tubes. These cells are 

 nucleated and usually quite granular. It has been found that, in many of the lower orders 

 of animals, the cells lining the neck of the capsule are provided with vibratile cilia ; and 

 it is possible that they may exist in man, although their presence has never been actually 

 demonstrated. 



The course of the tubes, after they have lost the characters which were formerly sup- 

 posed to be peculiar to the tubes of the cortical substance, and their anastomoses, have 

 attracted much attention within the last few years. It has- been shown by Henle, and 

 the most important points in his observations have been confirmed by numerous anato- 

 mists, that the convoluted tubes, instead of connecting directly with the tubes of the 

 pyramidal substance, are continuous with a system of smaller tubes, which pass into the 

 pyramids in the form of loops. 



Narrow Tubes of Henle. According to the most recent observations, the convoluted 

 tubes above described, after a long and tortuous ramification in the cortical substance, 

 invariably become continuous, near the pyramids, with tubes of much smaller diameter, 

 which form loops, extending to a greater or less depth into the pyramids. The loops 

 formed by these canals (the narrow tubes of Henle) are nearly parallel with the tubes of 

 Bellini and are much more numerous near the bases of the pyramids than toward the 

 apices. The diameter of these tubes is very variable, and they present enlargements at 

 irregular intervals in their course. The narrow portions are about yjnnr f an mc ^ m 

 diameter, and the wide portions, about twice this size. The narrow portion is lined by 

 small, clear cells with very prominent nuclei. The wider portions are lined by larger, 

 granular cells. Near the bases of the pyramids, the wide portion sometimes forms the 

 loop ; but, near the apices, the loop is always narrow. The difference in the size of the 

 epithelium is such, that, while the diameter of the tube is variable, its caliber remains 

 nearly uniform. The membrane of these tubes is quite thick, thicker, even, than the 

 membrane of the tubes of Bellini. 



Intermediate Tubes. After the narrow tubes of Henle have returned to the cortical 

 substance, they communicate with a system of flattened, ribbon-shaped canals, measuring 

 from y^-fr to T oYo f an m ch in diameter, with excessively thin, fragile walls, lined by 



