URINARY ORGANS IN THE VERTEBRATA. 105 



CHAPTER XX. 



URINARY ORGANS IN THE VERTEBRATA. 

 PISCES. 



The kidneys in this class are long and narrow, sometimes extend- 

 ing the whole length of the abdomen, as in the burbot. They 

 generally present the appearance of forming but a single mass, 

 their separation being only indicated by the presence of the ureters 

 and the cava. The ureters, which arise by numerous fine radicles, 

 soon unite in all the osseous fishes, into a single tube, which forms 

 a heart shaped dilatation previous to its termination behind the 

 anus, in common with the sexual organs. 



Bladder. — This reservoir is absent from all the osseous, and 

 several of the cartilaginous fishes, as the ray and shark, in which 

 the ureters open as in birds, into a cloaca: when it is present as in 

 the lump-fish, it receives the ureters anteriorly, and opens behind 

 the anus in common with the vasa deferentia. 



H 



AMPHIBIA. 



The kidneys are more distinct in this class than in fish. They 

 are greatly lengthened in the aquatic genera, but are much shorter in 

 the frog. The ureters convey the urine to the bladder, which is 

 situated in front of the rectum : in the frog it is of considerable size, 

 its walls are thin, and its fundus presents' two cornua. In the rep- 

 tilia the kidneys afford but few peculiarities, being elongated in the 

 lizard, as in fish, and somewhat oval in the tortoise. The ureters 

 are longer in this class than in the amphibia, and discharge them- 

 selves either into the cloaca or bladder. This organ is absent from 

 the ophidia, and several of the sauria, as the lizard, and the croco- 

 dile. It is very large in the chelonia, as the tortoise, and it is sin- 

 gular, that the ureters instead of going to it, empty themselves into 

 the urethra in front of it, so that the urine has to re-ascend to the 

 urinary reservoir. 



AVES. 



In this extensive oviparous class the kidneys are of great length, 

 extending along the spine, from the lungs to the lower end of the 

 rectum. These organs are relatively larger in birds than in the 

 terrestrial mammalia — a circumstance which is explained by recol- 

 lecting the nature of their integuments, and the little transposition 

 they admit of. They are of small size in the bustard and heron, 

 and their lower extremities are somewhat blended together in the 

 coot. Their structure is remarkable for the absence of cortical 

 portion ; the tubuli uriniferi run to the surface, and by their con- 



