468 HANDBOOK OF PHYSIOLOGY. 



the cortical portion, while others arise directly as small branches of the 

 renal arteries. 



Between the tubes, vessels, etc., which make up the substance of 

 the kidney, there exists, in small quantity, a fine matrix of areolar 

 tissue. 



Nerves. The nerves of the kidney are derived from the renal plexus 

 of each side. This consists of both medullated and non-medullated 

 nerve-fibres, the former of varying size, and of nerve-cells. The renal 

 plexus is derived from the solar plexus, particularly from the semilunar 

 ganglion. The renal plexus is thus indirectly connected with the vagi and 

 with the splanchnic nerves. It is also directly connected with them by 

 fibres which pass to them without first joining the solar plexus. Fibres 

 from the anterior roots of the eleventh, twelfth, and thirteenth dorsal 

 nerves in the dog also pass to the same plexus, either directly through 

 the sympathetic chain or by first passing into the solar plexus. 



Fig. 297. Epithelium of the bladder; a, one of the cells of the first row: b, a cell of the second row; 

 c, cells in situ, of first, second, and deepest layers. (Obersteiner.) 



The Ureters. The duct of each kidney, or ureter, is a tube about 

 the size of a goose-quill, and from twelve to sixteen inches in length, 

 which, continuous above with the pelvis of the kidney, ends below by 

 perforating obliquely the walls of the bladder, and opening on its inter- 

 nal surface. 



Structure. It is constructed of three principal coats (a) an outer, 

 tough, fibrous and elastic coat; (b) a middle muscular coat, of which the 

 fibres are unstriped, and arranged in three layers the fibres of the cen- 

 tral layer being circular, and those of the other two longitudinal in 

 direction; and (c) an internal mucous lining continuous with that of 

 the pelvis of the kidney above, and of the urinary bladder below. The 

 epithelium of all these parts (fig. 297) is alike stratified and of a some- 

 what peculiar form ; the cells on the free surface of the mucous mem- 

 brane being usually spheroidal or polyhedral with one or more spherical 

 or oval nuclei; while beneath these are pear-shaped cells, of which the 

 broad ends are directed toward the free surface, fitting in beneath the 

 cells of the first row, and the apices are prolonged into processes of va- 



