202 



SPECIAL HISTOLOGY. 



In fact, each interlobular artery gives off, in its whole length, on 

 two, three, or four sides, a great number of fine twigs possess- 

 ing the structure of arteries and 0-008 — 0-02"' in diameter, 

 which, after running a short distance, either directly or after 

 dividing once, penetrate the tunic of the Malpighian body, 

 becoming the vasa afferentia of its vascular coil. Each of 

 these (fig. 247, 248) consists of a close convolution of fine 



vessels 0-004— 0-008'" in dia- 

 meter, having the usual struc- 

 ture of capillaries (structure- 

 less coat and nuclei) and 

 possesses, besides the affe- 

 rent artery, an efferent vessel, 

 the vas eff evens. The mode 

 in which these two vessels 

 are connected is not that 

 which usually obtains in ar- 

 teries and veins, but corres- 

 ponds with the arrangement 

 presented in the bipolar retia 

 mirabilia, as they are termed • 

 the vas afferens, immediately 

 after its entrance into the 

 coil, dividing into 5 — 8 

 branches and each of these 

 into a bundle of capillaries, 

 which are much convoluted 

 and interlaced, without anastomosing, and ultimately, in the 

 same way as that in which they were formed, re-unite into a 

 single trunk. Usually the two main vessels enter and quit 

 the glomerulus near together, opposite the origin of the urini- 

 ferous duct, and its finest vessels of 0*003 — 0-004'", the 

 peripheral loops as it were, are invariably situated exactly at the 

 commencement of the duct. In Birds, Amphibia, and Fishes, 

 each glomerulus consists of a single convoluted vessel. 



The vasa efferentia, although composed of capillaries, are 



Fig. 248. From the Human kidney, after Bowman : a, extremity of an interlobular 

 artery; b, afferent arteries; c, naked glomerulus; d, efferent vessel ; e, glomeruli, 

 surrounded by the Malpighian capsules ; /, tubuli uriniferi springing from them ; 

 x 45 diam. 



