84 PRACTICAL HISTOLOGY. 



THE KIDNEYS. 



THE COURSE AND THE STRUCTURE OF THE URINARY 



TUBULES. 



THE course of the uriniferous tubules is very complicated, and the epithelium differs in different 

 sections of the tubules. 



The urinary tubules begin as a blind extremity at the Malpighian corpuscle, and open on 

 the free surface of a papilla. Every tubule consists of the following sections, which are con- 

 tinuous with each other. 



(l) The Malpighian capsule, which passes by (2) a short, narrow neck or constriction into (3) 

 the proximal convoluted tube, which passes into (4) the spiral tubule (Schachowa), lying in 

 a pyramid of Ferrein. All the above lie in the cortex. As the spiral tube passes from the 

 cortex into the boundary layer, it suddenly becomes straight and narrow as (5) the descending 

 limb of Henle's loop, which is continued into the beginning of the papillary portion, where it 

 bends on itself and forms (6) Henle's loop, which ascends into the boundary layer, where it 

 suddenly enlarges and becomes slightly wavy, to form (7) the first thick part of tlie ascending 

 limb of Henle's loop. It again becomes narrow and spiral, when it forms (8) the spiral part of 

 the ascending limb. It now (9) re-enters the cortex, and, becoming narrower, ascends in a 

 pyramid of Ferrein, which it soon leaves, and enters the labyrinth amongst the convoluted 

 tubules, as (10) the irregular tube, so called because of its irregular size, breadth, and course. 

 This passes into (Ilj the intercalated segment (schwelgger-Seldcl) which is the distal convoluted 

 tube, exactly like (3). It passes into (12) the curved part of the collecting tube, a narrow curved 

 tube which passes through the labyrinth, where it is joined by other similar tubes, and forms 

 (13) the straight part of the collecting tube, which descends in a pyramid of Ferrein, and then 

 enters the boundary portion, and finally passes into the papillary portion, there to be joined by 

 other branches, and form a large (14) collecting tube, opening on the free surface of a papilla 

 (Klein). 



The membrana propria of Bowman's capsule is continuous throughout all the sections of 

 the urinary tubules, but its epithelial lining varies greatly in different parts of its course. 



Bowman's capsule is lined with a single layer of squames ; the proximal convoluted tubule 

 (3) with a single layer of low nucleated columnar epithelial cells, which leave a lumen the size 

 of one-third the diameter of the tube. All the other sections of the tube, except the de- 

 scending part of Henle's loop (5), and all the parts of the collecting tube ( 1 2, 13, and 14) are lined 

 with polyhedral nucleated epithelial cells, whose outer half contains vertically placed ' reds ' or 

 fibrils (p. 87). 



The descending limb of Henle's loop (5 and 6) is lined with a layer of very flat transparent 



