i88o 



HUMAN ANATOMY. 



Fig 1603. 



apparent, since the close relations of glomerulus and capsule result from the growth of the latter 

 around the vascular tuft and not from invagination of the dilated tubule. The capsule consists 



of a distinct membrana propria and a lining composed 

 of a single layer of flat, plate-like cells, the modified 

 epithelium of the uriniferous tubule. In sections pass- 

 ing through the afferent vessel and the neck the lumen 

 of the capsule appears crescentic in outline, since the 

 space between its outer and inner walls is widest at 

 the neck and reduced to a mere slit where the two 

 layers are continuous around the narrow stalk tra- 

 versed by the afferent and efferent vessels. The inner 

 or "visceral" layer of the capsule, the thicker of the 

 two, is firmly attached to the glomerulus by the deli- 

 cate intervening connective tissue, the entire complex 

 appearing rich in nuclei which belong to the epithe- 

 lium of the capsule, the endothelium of the capillaries, 

 and the connective-tissue cells. 



2. The Proximal Convoluted Tubule. — After un- 

 dergoing the conspicuous constriction marking the 

 ticck of the capsule, the uriniferous tubule abruptly 

 enlarges into the convoluted segment which forms ap- 

 proximatel)- one-fifth of the length of the entire canal 

 and has a diameter of from .040-.060 mm. In com- 

 mon with other parts of the tubule, its wall consists of a 

 membrana propria, apparently structureless, but com- 

 posed of a delicate reticulum and intervening homoge- 

 neous substance and a single layer of epithelial cells. 

 Although the histological details of the latter 

 vary in different, but not constant, parts of the convo- 

 luted segment, the lining cells present certain charac- 

 teristics, chief among which is the differentiation of 

 the cytoplasm of the cells into a broader outer and 

 a narrow inner zow^. The former exhibits coarse radial striations, the so-called "rods," pro- 

 duced by rows of granules within the vertically disposed threads of spongioplasm (Rothstein) 

 which occupy approximately the pe- 



FiG.* 1 604. 



Blood-vessel 



Convoluted tubules, cut transversely aiid ob- 

 liquely, showing character of epithelial lining 

 X 400' 



ecting 



tubule 



Blood- 

 essel 



ripheral half of the cell extending 

 from the membrana propria towards 

 the inner zone. The latter, next the 

 lumen, usually appears as a well- 

 defined narrow border which, when 

 successfully preserved, presents a 

 fine vertical striation ("bristle bor- 

 der") that depends not upon rows 

 of granules, as do the rods of the outer 

 zone, but upon the disposition of 

 the threads of the spongioplasm. In 

 consequence of maceration and other 

 post-mortem changes, the inner zone 

 may undergo partial disintegration 

 and break up into short hair-like rods 

 which have been mistaken for cilia. 

 Although the spherical nuclei (.005- 

 .007 mm.) of the epithelium of the 

 convoluted tubule are sharply de- 

 fined, the demarcations between the 

 individual cells are obscure and often 

 v/anting, the tubule being lined by a 

 seemingly continuous nucleated layer 

 or syncytium. The lumen is not 

 uniform throughout the convoluted 

 tubule, in some places being wide and 

 in others reduced to mere clefts; these 

 differences depend chiefly upon the 

 varying height of the epithelial lining. 



3. The Spiral Tubule. — Following the tortuous path of the convoluted tubule, the canal is 

 usually continued into the medullary ray by a segment which, while comparatively straight, de- 



Portion of medullary ray 



Blood-vessel 

 showing spiral and collecting tubules. X 400. 



