282 VERTEBRATE ZOOLOGY 



is usually an accumulation of fat. On the medial side of the 

 kidney is the concavity called the hilus, where the ureter and the 

 renal vein leave it and the renal artery enters it. 



The ureter is a long tube which passes along the dorsal body 

 wall on one side of the vertebral column, from the kidney to the 

 dorsal surface of the bladder; it has the appearance of a white 

 cord and is often embedded in fat. Its anterior end is called the 

 pelvis ; this is a funnel-shaped sac, the large end of which is em- 

 bedded in the kidney and catches the urine as it oozes from the 

 mouths of the kidney tubules, while its small end emerges from 

 the hilus as the ureter proper. In the male animal each ureter, 

 near its hinder end, passes through a loop made by the vas de- 

 ferens, which also appears as a white cord. 



Remove the fat from the kidney and the ureter on the right 

 side of the animal, being careful not to cut the ureter or any of 

 the veins or arteries near it. The large median vein between the 

 kidneys is the postcaval vein; the large median artery is the 

 dorsal aorta. The renal vein and the renal artery on each side 

 will also be seen. 



The bladder, the posterior portion of the ureters, and the uro- 

 genital canal lie partially within the pelvic arch, which supports 

 the hind legs, and will be more or less concealed by its ventral 

 portion when the animal being dissected is lying on its back. 

 This portion is formed by two pairs of bones, the pubes and 

 the ischia, the right and the left member of which are joined 

 in the midventral line by a suture called the pelvic symphysis. 

 Cut through this symphysis (it can usually be done with a scalpel) 

 and spread the legs well apart. 



The urinary bladder is a muscular, pear-shaped sac which lies 

 in the hinder part of the abdominal cavity between the rectum 

 and the ventral body wall. Its larger end is directed forward ; its 

 smaller end, the neck, is directed backward. In the male animal 

 the neck is continued in the form of the urethra, or urogenital 

 canal, and receives the two vasa deferentia, which bring sper- 

 matozoa from the testes ; it then passes through the penis, at the 

 distal end of which is the external opening, and becomes thus the 

 common outlet for both urinary and genital organs. In the female 



