VIII 



THE EXCRETION OF URINE 



421 



the papillae into the calicos of the renal sinus. Each tubular 

 orifice with its multiple ramifications represents a pyramid of 

 Ferrein the morphologi- 

 cal unit from which the 

 pyramids of Malpighi arise. 

 For physiologists the 

 chief interest attaches to 

 the structure of the differ- 

 ent parts of the uriniferous 

 tubules, and the epithelial 

 cells with which these are 

 lined, in the hope of dis- 

 tinguishing the secretory 

 portion of the tubules from 

 such parts as simply con- 

 duct the urine. 



Bowman's capsule, 

 which surrounds the 

 glomerulus as the serous 

 coat surrounds the viscera, 

 consists of an external 

 layer, formed of a struc- 

 tureless basement mem- 

 brane, lined with flattened 

 epithelium, and an internal or visceral layer which lines the 



glomeruli, and dips down 

 between the loops and lobules. 

 In the adult its cells do 

 not form a definite and con- 

 tinuous layer (Fig. 111). In 

 the foetus, on the contrary 

 (when the vascular loops of 

 the glomerulus are still un- 

 developed), the stratum of 

 cells that completely sur- 

 rounds the glomerulus is 

 much more distinct (Fig. 112). 

 There is an intracapsular 

 space between the two layers, 

 which almost disappears when 



FIG. 112. Section of cortical substance of kidney ; the VCSSels of the glomerulus 

 human foetus. Highly magnified. (Klein.) a, . . -, -, , . , 



glomerulus with blood-vessels not fully developed ; are injected \ and. WniCn COni- 



b, connective tissue between the blood-vessels ; c, Tniin ; nn f p a frpplv with the* 



epithelium covering it continuous with d', flattened J L1 ^ V w 1 1 



Bowman's capsule ; /, /, con- 



FIG. 111. Structure of a Bowman's capsule from cortical 

 substance of human kidney. (Bohm and v. Davidoff.) 

 a, basement membrane of outer layer of capsule ; e, 

 epithelium of capsule ; eg, glomerular epithelium ; 

 vs, section of blood-vessel; 1, 2, 3, k, 5, lobules of 

 glomerulus ; co, neck at commencement of uriniferous 

 tubule, lined transitional epithelium ; ep, epithelium 

 of convoluted tubule. 



neck of a convoluted tubule, 

 where transitional forms 

 between the flattened epithelium of the outer layer of the capsule 

 and the cubical cells that line the tubules, may be detected. 



