THE URINARY ORGANS. 



203 



not veins, bnt in their nature, and to some extent in their 

 structure, minute arteries, a character that they retain until, in 

 their further course, they are merged in the capillary plexus 

 of the kidney. This plexus exists in the cortical substance and 

 in the pyramids, presenting somewhat different characters in 

 these two situations. In the former (fig. 245, d) the vasa 

 efferenlia 0-004 — 0-008'" in size, after a short course, terminate 

 in a very rich plexus of capillaries 0*002 — 0*004 — 0006'" in 

 diameter, the rounded-angular meshes of which, 0*005 — O'OIS'" 

 wide, encompass the convoluted tubuli on all sides and must be 



Fig. 249. 



regarded as continuous throughout the 

 whole cortical substance. The efferent 

 vessels of the glomeruli in nearest con- 

 tiguity to the Malpighian pyramids 

 alone present an exception to this 

 condition, inasmuch as, characte- 

 rised by their more considerable size 

 (001— 0*016'"), they are distributed 

 not in the cortical substance, but in 

 the pyramids, and are distinguished by 

 their long, straight course, and upon 

 the whole, scanty ramifications. These 

 vessels (fig. 245 g), which, with Arnold, 

 I would term arterioles recta, penetrate 

 around the entire circumference of the 

 pyramids, in a straight course, be- 

 tween the ducts of Bellini, and descend, 

 repeatedly dividing at acute angles, 

 and gradually attenuated to the dia- 

 meter of 0*004 — 0*01'", towards the 

 papillae, in which, as in the inte- 

 rior of the medullary substance (in 

 the latter situation, either by their 



extremities or by twigs given off at right angles), they are 

 continuous with the capillaries in those regions, measuring 

 from 0*002 to 0*004'". These capillaries are very importantly 



Fig. 249. Glomerulus from the innermost part of the cortex of the kidney of the 

 Horse, after Bowman: «, arter. interlobular is / af, vas afferens ; m m, glomerulus ; 

 ef, vas efferens s. arjeriola recta ; b, divisions of the same in the medullary sub- 

 stance ; x 70 diam. 



