CHAP. XIII.] 



THE GAT'S PLACE IN NATURE. 



471 





this account the milk is injected hy the mother into the young 

 while it hangs attached by its mouth to the nipple. The injecting 

 action is effected hy the cremaster muscle, which embraces the 

 mammary glands of the females and the testes of the males. The 

 testes hang in a scrotum ; hut this receptacle is placed in front of 

 the penis instead of, as in the cat, behind it. All marsupials have 

 marsupial bones except the Thylacine, which has them represented 

 by large marsupial cartilages. The internal carotid artery enters 

 the cranium through a foramen in the sphenoid bone. The mandible 

 has its "angle" inflected. The palate has commonly certain 

 apertures due to defect of ossification. The corpus callosum is very 

 small, and the anterior commissure is large. In such marsupial 

 forms as are carnivorous, the molar teeth are not differentiated into 

 premolars, sectorials, and tubercular teeth as in the cat and other 

 placental carnivora and there are never six incisors above and six 

 below. Thus the cat, as a MONODELPHOUS MAMMAL, differs from 

 the DIDELPHIA in that : 



(1) The vagina is single. 



(2) The young are brought forth in a well- developed condition. 



(3) There is no " pouch " and the young can suck as soon as born. 



(4) There are never marsupial bones or large * marsupial 



cartilages. 



(5) The mammae are not embraced by the cremaster. 



(6) The scrotum being present f is behind the penis. 



(7) The internal carotid does not perforate the sphenoid. 



(8) The corpus callosum is large and the anterior commissure 



small. 



(9) The angle of the mandible is not inflected. $ 



(10) There are six incisors in both the upper and lower jaw. 



(11) Reproduction takes place by the aid of an allantoic placenta. 

 20. Such being the characters which respectively distinguish 



the cat as a monodelphous mammal from both the mammalian 

 sub-classes which are not monodelphous, we have next to compare 

 its ORDER with the OTHER ORDERS of its own sub-class Monodelphia. 



Its order, Carnivora, containing the creatures we have already 

 seen it to contain, is easily distinguishable from the two orders 

 Sirenia and Cetacea, because in both the latter the pelvic limbs are 

 entirely wanting, or only represented by rudiments not externally 

 visible. 



The Carnivora are distinguished from all animals of the order 

 Edentata by possessing median upper incisors, with unequivocal canines 

 and with molars provided with cutting edges or tubercular prominences 

 or both. From the anteaters they differ in that they are furnished with 

 teeth ; from the pangolins, in that they are not clothed with horny 

 overlapping scales ; from the armadillos, in that their skin does not 

 develop calcareous plates ; from the Orycteropus, in that each tooth 



* In the dog there are very small mar- 

 supial cartilages, 

 t Not all monodelphous mammals have 



a scrotum. 



t It is so however in the monodelphot 

 mammal the Tanrec (Centetes). 



