372 



FXCRETION 



which begin at the opening on the Malpighian pyramid and, after a devious 

 course, end in the capsule of the glomerulus. 



Tubuli Uriniferi. The tubuli uriniferi, figure 287, are composed 

 of a nearly homogeneous membrane, and are lined internally by epithelium. 

 They vary considerably in size in different parts of their course, but are, 

 on an average, about 40 fj. in diameter, and are found to be made up of several 

 distinct sections. The first section or part to be identified is the Malpi- 



FIG. 286. Longitudinal Section of Kidney through Hilum. a, Cortical pyramid; b, medullary 

 ray; c, medulla; d, cortex; e, renal calyx; f, hilum; g, ureter; h, renal artery; *, obliquely cut tubules 

 of medulla; / and k, renal arches; /, column of Bertini; m, connective tissue and fat surrounding 

 renal vessels; n, medulla cut obliquely; o, papilla; p, medullary pyramid. (Merkel-Henle.) 



ghian, or Bowman's, capsule, figure 287. It is composed of a hyaline membrana 

 propria, thickened by a varying amount of fibrous tissue, and lined by flattened 

 nucleated epithelial plates. This capsule is the dilated extremity of the 

 uriniferous tubule which is invaginated to receive the glomerulus of con- 

 voluted capillary blood-vessels. The invaginated portion of the tubule is of 

 particular importance since it is the membrane through which a large part 

 of the urine is secreted. The glomerulus is connected with an efferent and 

 an afferent blood-vessel. The Malpighian capsule is connected by a con- 

 stricted neck, figure 287, N, with the proximal convoluted tubule. This forms 



