422 



EXCRETION 



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^ in diameter, and are found to be made up of several 

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

 pighian, or Bowman's capsule, figure 287. It is composed of a hyaline mem- 

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



a b 



FIG. 286. Longitudinal Section of Kidney through Hilum. a, Cortical pyramid; 6, 

 medullary ray; c, medulla; d, cortex; e, renal calyx;/, hilum; g, ureter; h, renal artery; , 

 obliquely cut tubules of medulla; j 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.) 



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, TV, with the proximal convoluted tubule. This forms 

 several distinct curves and is lined with short columnar cells. The tube 



