318 MAESUPIALIA. 



always so disposed round the mammsB as to form a pouch, in which these 

 imperfect young are preserved as in a second uterus ; and into which, long 

 after they can walk, they retire for shelter on the apprehension of danger. 

 Two peculiar bones attached to the pubis, and interposed between the 

 muscles of the abdomen, support the pouch and prevent inconvenient pres- 

 sure of the young, when grown, upon the bowels. These bones are also 

 found in the male, and even in those species in which the fold that forms 

 the pouch is scarcely visible. The matrix of the animals of this order 

 does not open by a single orifice into the extremity of the vagina, but 

 communicates with this canal by two bent lateral tubes. The premature 

 birth of the young appears to depend on this singular organization. The 

 scrotum of the male, contrary to what obtains in, other quadrupeds, hangs 

 before the penis, which at rest is directed backwardsi 



The members of this group are lower in their organization than any 

 other mammiferous animals, approximating the oviparous type, and parti- 

 cularly reptiles, in sundry details of their conformation. The hemispheres 

 of the brain, which is small, are not united by a corpus callosum ; and 

 they are observed to be very defective in intelligence, as is indicated by 

 their physiognomy ; the blood is returned to their heart by two prin- 

 cipal veins as in Birds and Eeptiles ; and the sutures of the skull never 

 become united. In short, they hold an analogous relation towards other 

 Mammalia to that which the Batracliia present to all other reptiles. 

 Tlieir incisor teeth frequently exceed six in number, which is the maxi- 

 mum throughout the rest of their class, another indication of their 

 inferiority.* 



Although they all show a general resemblance to each other in this pe- 

 culiar structure and organization, yet they differ so much in the teeth, 

 digestive organs, feet and external form, that they sub-divide into several 

 distinct families, or sub-orders, which by some are ranged parallel to the 

 orders of Placental Mammals ; and they are, by a few, looked on as 

 degraded types of these last, or rather, that their inferiority of type is a 

 sign of their earlier introduction, and that Nature has advanced in organi- 

 zation since the earlier types were formed. The earliest fossil Mammals 

 belong to this order. All are from the Australian region except one 

 group, the Opossums, found in South America, and Central America as 

 lar north as Virginia. 



* CuTierV Animal Kingdom, English trantjlatlon. 



