STRUCTURE OF THE TUBULES. 



389 



space between the glomerulus and the capsule into which the filtered urine passes. The neck 

 is lined by cubical cells. These cells, in some animals, e.g., the rabbit, sheep, mouse, and frog, 

 are ciliated. 



The proximal convoluted tubule is lined by characteristic epithelium. The cells, which are 

 short or polyhedral, contain a 

 turbid or cloudy protoplasm (fig. 

 244, III, 1 and 2), which notun- 

 frequently contains oil-globules, 

 and they form a single layer. 

 Each cell consist of two parts ; 

 the inner, containing the spheri- 

 cal nucleus, is next the lumen, 

 and granular (III, 2, g), while 

 the outer part, next the mem- 

 brana propria, appears fibril- * 

 lated, or "rodded," from theft 

 presence of rods or fibrils placed 

 vertically to the basement-mem- 

 brane (fig. 245). These appear 

 like the hairs of a brush pressed 

 upon a plate of glass (III, 2). 

 The cells are not easily separated 

 from each other, as neighbouring 

 cells interlock by means of the 

 branched ridges on their sur- 

 faces (III, 1 ) ( Hcidenhain, 

 Schachowa). The lumen is well 

 defined, but its size seems to 

 depend upon the state of imbibi- 

 tion of the cells bounding it. 



The spiral tubule has similar 

 epithelium and a corresponding 

 lumen, although the epithelium 

 becomes lower and somewhat 

 altered in its characters at the 

 lower part of the tube. 



The descending limb of 

 Henle's loop, and the loop itself . 

 with a relatively wide lumen, 

 are bounded by clear, flattened, 

 epithelial cells, with a bulging 

 nucleus (IV, S) ; the cells lying 

 on one side of the tube being so 

 placed that the bulging part of 

 the bodies of the cells is oppo- 

 site the thin part of the cells on 

 the opposite side of the tube. 

 [These tubes might be mistaken 

 for blood-capillaries, but in ad- 

 dition to their squamous lining, 

 they have a basement-membrane, 

 which capillaries have not] In 

 the ascending limb, the lumen 

 is relatively wide, while its epi- 

 thelium agrees generally with 

 that in the convoluted tubule, 

 excepting that the "rods" are T 

 shorter. Sometimes the cells 

 imbricate " 



are arranged in an 

 manner. 



In the irregular tubule, which 

 has a very small lumen, the 

 polyhedral cells lining it contain 

 oval nuclei, and are shorter than 

 those of the convoluted tubules. 



Fig. 243. 

 Blood-vessels and uriniferous tubules of the kidney (semi- 

 diagrammatic); A, capillaries of the cortex, B, of the me- 

 dulla; a, interlobular artery ; 1, vasafferens; 2, vas efferens; 

 r, e, vasa recta ; c, venae rectae ; v, v, interlobular vein ; S, 

 origin of a vena stellata; i, i, Bowman's capsule and glo- 

 merulus ; X, X, convoluted tubules ; t, t, Henle's loop ; n, n, 

 junctional piece ; 0, 0, collecting tubes ; 0, excretory tube. 



The cells, again, are very irregular in size, while their 



rodded" character is much coarser and more defined (fig. 246). 



The distal convoluted tubule closely resembles in its structure the proximal convoluted 



