342 



SPLANCHNOLOGY. 



capilliary blood-vessels, arranged in a tuft or glomurulus, sur- 

 rounded by epithelium, and enclosed in a membranous capsule, 

 the capsule of Bowman, which is the dilated origin of a 

 uriniferous tube. The small branch of the renal artery, entering 

 the capsule, is the afferent vessel (vas afferens), whence proceed 

 the capillaries which form the tuft. The efferent vessel (vas 

 efFerens), which leaves the tuft near the afferent one, forms a 

 capillary plexus round the adjacent tubes, terminating in th(^ 

 veins. A dark line separates the cortical from the medullary 

 layer, and has been termed the limiting layer, or periphery of the 

 medulla. In or near this layer the larger blood-vessels ramify.. 

 The medullary substance is denser in structure, fibrous in 

 appearance, and consists of pale, conical 

 masses — the pyramids of Malpighi ; these 

 have their bases directed outwards, their 

 apices converging to the pelvis, and are 

 composed of minute diverging uriniferous 

 tubes, separated from each other by capil- 

 lary vessels and intermediate tissue, similar 

 to that of the cortical substance. The 

 termination of the pyramids in the pelvis 

 varies in different animals. In the horse 

 they terminate in a continuous ridge, which 

 projects into the pelvis ; and on the surface 

 of this ridge are numerous minute orifices, 

 the outlets. In the centre of the kidney, 

 and nearly surrounded by the medullary 

 substance, is an irregular cavity formed by 

 the dilatation of the ureter, the infundi- 

 hulum, having lateral prolongations called 

 the arms, the whole constituting the pelvis. 



The urine secreted by the tubuli uriniferi and Malpighian 

 bodies is thus poured into the pelvis. The tubes pass up the 

 pyramids in straight but slightly diverging lines, subdividing at 

 very acute angles until they reach the cortical substance, where 

 they dilate and become ' tortuous ; this part has been termed an 

 intermediary tube, and from it a constricted tube passes inwards, 

 dipping more or less into the medullary layer, and then returning 

 to the cortex, so forming a loop. To the looped tube succeeds a 

 second dilated portion, greatly convoluted, and known as a con- 

 voUited tube, which finds its origin in a dilatation — one of the 



Fio. 122. 

 Distribution of the renal 

 vessels, a, Branch of renal 

 artery ; of, Afferent vessels ; 

 m, Malpighian tuft ; ef, Efifer- 

 ent vessels ; p, Capillary plex- 

 us around the uriniferous 

 tubes ; st, Straight tube ; ct. 

 Convoluted tube. 



