VIII 



THE EXCRETION OF URINE 



421 



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

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

 epithelium of capsule ; eg, glomerular epithelium ; 

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

 glomerulus ; co, neck at commencement of uriniferous 

 tubule, lined transitional epithelium ; ep, epithelium 

 of convoluted tubule. 



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 J.../ 

 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 tne SerOUS p IO m_ structure of a Bowman^ capsule from cortical 



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 

 the vessels of the glomerulus 

 are injected ; and which com- 

 municates freely with the 

 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. 



Fir,. 112. Section of cortical substance of kidney ; 

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

 glomerulus with blood-vessels not fully developed ; 

 b, connective tissue between the blood-vessels ; c, 

 epithelium covering it continuous with d', flattened 

 epithelium lining Bowman's capsule ; /, /, con- 

 voluted tubes. 



