-572 \^ETERINARY PHYSIOLOGY 



cortex may be subdivided into these rays and the parts between 

 the rays — the labyrinth of the cortex. 



It is in this tliat the Malpighian bodies already described 

 are situated. 



Extending away from each of them is a proximal convoluted 

 tubule, also in the labyrinth {P.C.T.), lined by pyramidal and 

 granular epithelial cells. This dives into the boundary zone of 

 the medulla, becomes constricted and lined by a transparent 

 flattened epithelium, and is known as the descending livib of 

 the looped tubule of Henle. Turning suddenly upwards and 

 becoming lined by a cubical granular epithelium, it forms the 

 ascending limb, and, reaching the labyrinth of the cortex, it ex- 

 pands into the distal convoluted tubule (D.C.T.), Avhich resembles 

 the proximal. It opens into a collecting tubule, running in 

 a medullary ray, and (C.T.), lined by a low transparent epi- 

 thelium, which conducts the urine to the pelvis of the kidney. 



The renal artery breaks up and gives off a series of straight 

 branches — the interlobular arteries (IL.A.) — which, as they run 

 towards tJje surface, give off short side branches which terminate 

 in the glomeruli. The efferent vein passing from each glomerulus 

 breaks up again into a series of capillaries between the con- 

 voluted tubules, and these pour their blood into the interlobular 

 veins (IL.V.). This arrangement helps to maintain a high 

 pressure in the capillary loops of the glomerular tuft. 



Nerves to the kidney in the dog pass in the splanchnic 

 nerves from the anterior roots of the sixth to the thirteenth 

 dorsal nerves, and from the vagus, chiefly through the semilunar 

 ganglion, and the renal plexus upon the renal blood-vessels. 

 The terminal fibres not only supply the arterioles, but may be 

 traced into the secreting cells of the tubules. 



Apparently the old differentiation of the nephridium with 

 the arrangement for allowing the escape of coelomic fluid and 

 for the excretion of waste material is preserved in the vertebrate 

 kidney, but now the coelomic fluid is confined to blood-vessels 

 which are related to both the coelomic expansions and the 

 tubules. 



II. Physiology of the Formation of Urine. 



Bowman, from his investigations of the structure of the 

 kidney, but without giving consideration to its phylogenetic 



