HUMAN PHYSIOLOGY. 



(Fig. 20). From the apex to the base of the pyramids they are known as the 

 tubules of Bellini. In the cortical portion of the kidney each tubule becomes 

 enlarged and twisted, and after pursuing an extremely convoluted course, 

 turns backward into the medullary portion for some distance, forming the 

 descending limb of Henle's loop: it then turns upon itself, forming the ascend- 

 ing limb of the loop, ree'nters the cortex, again expands, and finally terminates 

 in a spheric enlargement known as Mutter's or 

 Bowman's capsule. Within this capsule is contained 

 a small tuft of blood-vessels, constituting the glomer- 

 ulus, or Malpighian corpuscles. 



Structure of the Tubules. Each tubule consists 

 of a basement membrane lined by epithelium cells 

 throughout its entire extent. The tubule and its 

 contained epithelium vary in shape and size in 

 different parts of its course. The termination of 

 the convoluted tube consists of a little sac or cap- 

 sule, which is ovoid in shape and measures about 

 ^ 7 of an inch. This capsule is lined by a layer of 

 flattened epithelial cells, which is also reflected over 

 the surface of the glomerulus. During the periods 

 of secretory activity the blood-vessels of the glomer- 

 ulus become filled with blood, so that the cavity of 

 the sac is almost obliterated ; after secretory activity 

 the blood-vessels contract and the sac-cavity be- 

 comes enlarged. In that portion of the tubule 

 lying between the capsule and Henle's loop the 

 epithelial cells are cuboid in shape; in Henle's loop 

 they are flattened, while in the remainder of the 

 tubule they are cuboid and columnar. 



Blood-vessels of the Kidney. The renal artery is of large size and 

 enters the organ at the nilum; it divides into several large branches, which 

 penetrate the substance of the kidney between the pyramids, at the base of 

 which they form an anastomosing plexus, which completely surrounds them. 

 From this plexus vessels follow the straight tubes toward the apex, while 

 others, entering the cortical portion, divide into small twigs, which enter 

 the Malpighian body and form a mass of convoluted vessels, the glomerulus. 

 After circulating through the Malpighian tuft, the blood is gathered together 

 by two or three small veins, which again subdivide and form a fine capillary 

 plexus, which envelops the convoluted tubules; from this plexus the veins 

 converge to form the emulgent vein, which empties into the vena cava. 



FIG. 20. DIAGRAM- 

 MATIC EXPOSITION OF 

 THE METHOD IN WHICH 

 THE URINI FERGUS 

 TUBES UNITE TO FORM 

 PRIMITIVE CONES. 

 (Tyson, after Ludwig.) 



