704 MAMMALIA. 



(828.) Even in Birds, as the reader will remember, the secre- 

 tions of the testes and of the kidneys were both poured into the 

 common cavity of the cloaca, and discharged through the anal 

 orifice. No bladder was provided for the reception of the urine ; 

 and a simple, grooved but imperforate penis, even where that 

 organ was most fully developed, was sufficient for the purposes of 

 impregnation. 



(829.) Widely different, however, is the arrangement of the 

 male genito-urinary system in the class we are now considering. 

 The cloacal cavity is no longer met with, the terminations of the 

 rectum and of the sexual ducts being now remotely separated ; the 

 penis is traversed by a complete urethral canal, through which the 

 seminal fluid is forcibly ejaculated ; and, moreover, subsidiary 

 glands, not met with in any of the preceding classes, add their se- 

 cretions to that of the testes, and thus facilitate the intromission 

 of the fecundating fluid. A urinary bladder is now superadded 

 to the renal apparatus, wherein the urine is permitted to accumu- 

 late in considerable quantities, prior to its expulsion through the 

 urethra, the excretory duct common to both the urinary and 

 generative organs. 



(830.) Not less remarkable are the corresponding changes ob- 

 servable in the disposition of the female reproductive organs. The 

 Mammifers are appointed to bring forth living young ; a uterine 

 receptacle is, therefore, necessarily provided for the reception of 

 the foetus, and mammary glands are given to support the tender 

 offspring during the earlier portion of its existence : but the history 

 of these organs cannot be laid before the reader at a glance, and 

 we must therefore patiently trace out their developement step by 

 step, and gradually ascend from the Oviparous type up to the most 

 complete forms of the genito-urinary system. 



(831.) Commencing with the urinary apparatus, the first parts 

 that offer themselves to our notice are the kidneys, the ureters, 

 and the bladder ; in describing which the same remarks will be 

 found applicable to both sexes. 



The kidneys in all the Mammiferous orders occupy a similar 

 position, being situated in the loins on each side of the aorta, from 

 whence they receive a copious supply of arterial blood by the renal 

 arteries, which, after having supplied the urinary secretion, is re- 

 turned to the circulation by the emulgent veins that empty them- 

 selves into the inferior cava. 



As relates to their intimate structure, the kidneys of all qua- 



