736 



THE URINARY TRACT. 



and the whole being turned upon itself, the two hands joining, 

 while the middle, broad portion, spread and folded, represents 

 the tuft. (See Fig. 330.) 



The tufts, or glomeruli, or Malpighian corpuscles, are globular 

 formations of 0.02 to 0.03 mm. diameter, composed of a number 

 of convolutions of capillary blood-vessels, which both in the 

 human and in the dog's kidney are arranged in two main lobes ; 

 hence, the glomerulus is a bilobate for- 

 mation of capillaries. One lobule is 

 always larger than the other, and the 

 summit of the larger lobule is directed 

 toward the opening of the uriniferous 

 tubule. Each tuft is enveloped in a 

 delicate connective-tissue capsule (Bow- 

 man, H. Miiller) in a manner similar to 

 that in which the pericardium surrounds 

 the heart. Both layers, the free or par- 

 ietal, as well as the reduplicated glo- 

 merular, are composed of connective tis- 

 sue rich in elastic substance, the glome- 

 rular portion being more delicate than 

 the parietal; both are covered with aflat 

 epithelial layer. The glomerular portion 

 sends prolongations between the capil- 

 laries of the tuft, and a marked prolong- 

 ation, together with the covering epithe- 

 lium, into the groove between the two 

 lobules of the tuft (Axel Key). The epithe- 

 lium covering the glomerular portion of 

 the capsule is cuboidal in the foetus and 

 in children, and becomes flattened in the 

 adult; while the epithelium of the par- 

 ietal portion of the capsule is always flat and blends with the 

 cuboidal epithelium of the uriniferous tubule, the beginning of 

 which it represents. At the point where the afferent vessel enters 

 and the efferent leaves the tuft, the capsule turns over to the 

 tuft, and the connective tissue at this point is more freely sup- 

 plied with plastids having the appearance of nuclei than else- 

 where. (See Fig. 331.) 



The efferent vessel invariably leaves the tuft near the entrance 

 of the afferent vessel ; it contains arterial blood, though the mus- 

 cle-coat is very imperfect, or absent. Its diameter is decidedly 



FIG. 330. DIAGRAM OF 

 THE TUFT (C. LUDWIG). 



A V, afferent vessel ; T, capil- 

 laries composing the tuft; EV, 

 efferent vessel ; C, capillaries 

 for the supply of the cortical 

 substance. 



