THORAX AND ABDOMEN OF THE HORSE 143 



The innermost zone of the medullary substance is often the palest 

 part of the section, and forms a curved ridge, the common renal 

 papilla^ (papilla renalis communis), running longitudinally to the long 

 axis of the kidney and projecting into a cavity known as the renal 

 pelvis (pelvis renalis). In conformity with the shape of the kidney as 

 a whole, the pelvis is elongated and crescentic, each horn of the 

 crescent being abruptly curved to form a terminal recess (recessus 

 terminalis). In the concavity of the crescent is the funnel-shaped 

 portion of the pelvis (recessus medius), from whicl^ the ureter arises. 



The ureter,- a tube about 7 or 8 mm. wide and some 65 to 70 cm. 

 long, leaves the central part (middle recess) of the renal pelvis, passes 

 through the renal sinus, and appears at the renal hilus. From the 

 hilus the duct runs backwards between the psoas minor muscle and the 

 peritoneum (in the subperitoneal tissue) and enters the pelvis to end 

 by obliquely piercing the dorsal wall of the urinary bladder. It may, 

 therefore, be divided into an abdominal part (pars abdominalis) and a 

 pelvic part (pars pelvina). Before the pelvis is reached, the ureter 

 crosses the ventral border of the deep circumflex iliac and external iliac 

 arteries : the internal spermatic artery crosses the ventral border of the 

 ureter. At the entrance to the pelvis, the ureter of the male crosses 

 the dorsal surface of the ductus deferens, and from this point is 

 associated with the urogenital fold (plica urogenitalis) of the peri- 

 toneum. In the female the greater part of the tube is enclosed in the 

 dorsal edge of the broad ligament of the uterus. 



The right and left ureters have the caudal vena cava and the aorta 

 respectively on their medial aspect, though they do not as a rule touch 

 these vessels. 



The terminal part of the ureter runs for 3 or 4 cm. between the 

 muscular tunic and the mucous lining of the bladder before opening 

 into this sac. As will be determined when the interior of the urinary 

 bladder is examined in a later dissection, the peculiar mode of termi- 

 nation of the ureter results in a valve-like closure of the tube against 

 the backward passage of urine into it from the bladder, but normally 

 no obstacle is offered to the flow of urine from the ureter into the 

 bladder. 



Adrenal glaxds (Glandulse suprarenales). — The adrenals or supra- 

 renal glands are two elongated, irregularly triangular bodies placed on 



* In a typical mammalian kidney the organ is divi.sible into renal pyramids 

 with bases directed towards the surface. The apices of the pyramids form papilla* 

 that project into the renal pelvis. In the horse the pyramids are indistinct and 

 their papillae are fused together into a ridge or crest, the common renal papillae. 



^ Ureter [L.], ovp-nrrip (oureter) [Gr.], urinary canal. 



