THE URETERS THE URINARY BLADDER 475 



and becomes tortuous, constituting the distal convoluted tubule. The tubule then narrows, 

 enters a medullarj^ ray, and opens with other tubules into a straight collecting tubule; this passes 

 axially tlirough a pyramid, and unites with other collecting tubules to form the relatively large 

 papillary ducts, which open into the renal pelvis. 



Stroma. — The interstitial tissue forms a reticulum throughout which supports the tubules 

 and l)lood-vessels. It is very scanty in the cortex, much more abundant in the medulla, in which 

 it increases in amount toward the pelvis. 



Blood-supply. — The kidnej's receive a large amount of l)]ood through the 

 renal arteries. Branches of these enter at the hilus and on the ventral surface of 

 the gland, and reach the intermediate zone, where they form anastomotic arches 

 (Arteriae arciformes). From these arciform arteries branches pass into the cortex 

 and medulla. The cortical branches (Arteriie interlobulares) have in general a 

 radial course between the cortical lobules, and give off short lateral branches, each 

 of which ends as the afferent vessel (Vas afferens) of a renal corpuscle. The blood 

 is carried from the glomerulus by a smaller efferent vessel, which breaks up im- 

 mediately into capillaries which form networks around the tubules. The medul- 

 lary branches descend in the pyramids, forming in them bundles of straight twigs 

 (Arteriolce rectae). 



The veins correspond in general to the arteries. In the superficial part of 

 the cortex the veins form star-like figures (Venae stellatae) by the convergence of 

 several small radicles to a common trunk. 



Lymph Vessels. — These may be divided into two sets, capsular or superficial, 

 and parenchymatous or deep. 



Nerve-supply. — The nerves are derived from the renal plexus of the sym- 

 pathetic, and form a plexus around the vessels. 



THE URETERS 



The ureters are the narrow jiart of the excretory ducts of the kidneys. Each 

 begins at the renal pelvis and terminates at the bladder. It is about ^ to | inch (ca. 

 6 to 8 mm.) in diameter, and its average length is about 28 inches (ca. 70 cm.). The 

 abdominal part (Pars abdominalis) of each ureter emerges ventrally from the hilus 

 of the kidney, and curves backward and inward toward the lateral face of the 

 posterior vena cava (right side) or the posterior aorta (left side). They then pass 

 almost straight backward in the subperitoneal tissue on the surface of the psoas 

 minor, cross the external iliac vessels, and enter the pelvic cavity. The pelvic 

 part (Pars pelvina) passes backward and a little downward on the lateral wall of 

 the pelvic cavity, turns inward, and pierces the dorsal wall of the bladder near the 

 neck. 



In the male the pelvic part enters the urogenital fold and crosses the vas 

 deferens. In the female the ureter is situated in the greater part of its coiuse in 

 the dorsal part of the broad ligament of the uterus. 



The wall of the ureter is composed of three coats. The outer fibrous coat 

 (Tunica adventitia) is composed of loose fibrous tissue. The muscular coat 

 (Tunica muscularis) consists of inner and outer layers of longitudinal fibers, with 

 a stratum of circular fibers between them. The mucous membrane (Tunica 

 mucosa) is covered with transitional epithelium; glands (Glandulae mucosae 

 ureteris) resembling those of the renal pelvis occur in the first three or four inches 

 of the ureter. 



THE URINARY BLADDER 



The urinary bladder (Vesica urinaria) (Figs. 270, 271, 272) differs in form, size, 



and position according to the amount of its contents. When empty and contracted, 



it is a dense, pyriform mass, about the size of a fist, lies on the ventral wall of the 



pelvic cavity, and does not reach to the inlet. When moderately filled, it is ovoid 



