THE ABDOMEN 819 



contorti), though there are also bundles of straight tubules {tubuli 

 recti) which have issued from the Malpighian pyramids, and form 

 the medullary rays or pyramids of Ferrein. 



Cortex. — The cortical part is composed of the labyrinth and the 

 medullary rays or pyramids of Ferrein. 



Labyrinth. — ^This portion of the cortex is so named from the very 

 complicated arrangement of its tubules. It is situated in the 

 interspaces between the medullary rays, and is composed of convo- 

 luted uriniferous tubules, bloodvessels, and Malpighian corpuscles, 

 each of which corpuscles is enclosed within a capsiile of Bowman. 



Uriniferous Tubules, — Each tubule commences in the labyrinth 

 of the cortex in a spherical dilatation, called the capsule of 

 Bowman, within which there is a tuft of convoluted capillary 

 bloodvessels, known as a glomerulus (Ruysch) or Malpighian 

 corpuscle. Bowman's capsule presents two poles. One of these 

 is formed by two bloodvessels, afferent and efferent, which pierce 

 the capsule at separate points, but close to each other. At 

 the other pole Bowman's capsule becomes constricted, and forms 

 the neck of a cylindrical tubule. After the tubule has passed the 

 neck it becomes convoluted, and forms the first or proximal convo- 

 luted tubule. The basement membrane and lining epithelium of 

 Bowman's capsule are continuous with the basement membrane 

 and lining epithelium of the proximal convoluted tubule, and 

 the space between Bowman's capsule and the glomerulus is con- 

 tinuous with the lumen of the tubule. The proximal convoluted 

 tubule soon becomes straight, though slightly wavy, and, entering a 

 medullary ray, it forms the spiral tubule. This tubule, on reaching 

 the junction of the cortex and boundary layer, becomes suddenly 

 very narrow, and traverses the boundary zone of a Malpighian 

 pyramid. It is known as the descending tubule of Henle. On 

 leaving the boundar^'^ zone it enters the papUlary zone, and after a 

 short course it describes a very sharp bend, called the loop of Henle's 

 tubule. It now retraces its steps from the papillary zone into the 

 boundary zone of a Malpighian pyramid, in which latter situation it 

 becomes suddenly enlarged. This part, which retraces its steps, 

 is called the ascending tubule of Henle. It re-enters the cortex, where 

 it becomes narrower, and passes into a medullary ray, in which 

 it lies for a short distance. It subsequently, however, leaves the 

 ray, and, entering the labyrinth, winds between the convoluted 

 tubules as the irregular or zigzag ttibule, which has become slightly 

 enlarged. This zigzag tubule then passes into the second or distal 

 convoluted (intercalary) tubule. This tubule, becoming narrow, 

 passes into the junctional or collecting tubule, which is slightly wavj\ 

 The junctional tubule leads into the straight collecting ttcbule 

 which is slightly enlarged, and is situated in a medullary ray. This 

 straight collecting tubule now passes to the boundary zone of a 

 Malpighian pyramid, taking up in its course other junctional 

 tubules from the labyrinth. In passing through the various parts 

 of a Malpighian pyramid the straight collecting tubules unite at 



