470 



THE CAT. 



[CHAP. xin. 



texture. Posteriorly the alimentary canal opens into a cloaca (as 

 in the Monocondyla) which also receives the terminations of the 

 ureters and generative ducts. Thus the ureters do not open into 

 the bladder, although a urinary bladder is fully formed. The penis 

 is perforated by a urethra, but this does not transmit the renal 

 secretion, as it is proximally discontinuous with the cystic urethra, 

 and serves but for the testicular product. There are two uteri, 

 which open side by side into the cloaca, so that there is no vagina 

 any more than in birds from which circumstance the name of the 

 sub-class is derived. The mammary glands pour out the milk from 

 numerous apertures on the surface of the skin, but these are not 

 aggregated into a distinct prominence or nipple. No allantoic 

 placenta is developed. Thus the cat, as a MONODELPHOUS MAMMAL, 

 differs from the lowest mammalian sub-class, the ORNITHODELPHIA, 

 by the following characters : 



(1) There is (in the female) a vagina. 



(2) There is no cloaca. 



(3) The cystic and spongy portions of the urethra are continuous, 



and it transmits the urine. 



(4) The ureters open into the bladder. 



(5) The mammary glands have teats. 



(6) The vertebrae ossify by terminal epiphyses. 



(7) Development is effected by the help of an allantoic placenta. 



(8) The cerebrum has a large corpus callosum and a small 



anterior commissure. 



(9) The ear has a complex, spirally coiled cochlea. 



(10) The coracoids are but small processes. 



(11) There are no epicoracoids or interclavicle. 



(12) The acetabula are imperforate. 



(13) There are no marsupial bones. 



(14) The fibula has no olecranon-like process. 



(15) There being teeth * they are calcareous. 



The animals of the order Marsupialia are all much more like the 

 cat in structure than are the Monotremes. Nevertheless they pre- 

 sent such important divergences from the structure of monodelphous 

 mammals, that the whale or bat may both be considered (they being 

 both monodelphous mammals) to be much more fundamentally like 

 the cat than is that opossum which has (on account of its superficial 

 resemblance to our subject) been called the " native-cat." 



In all the marsupials the vagina is double whence the name of 

 their sub-class, Didelphia. Their process of development takes place 

 in such wise that the young are brought forth in an extremely 

 imperfect condition. They are, therefore, in the great majority of 

 marsupials, sheltered for a time within a " pouch," (consisting of a 

 fold of the skin of the belly) within which are the nipples. Their 

 young are not developed by means of an allantoic placenta, and when 

 born, are so feeble and imperfect that they are unable to suck. On 



Some Monodelphous mammals, as we have seen, have no teeth at all. 



