MARSUPIALIA AND MONOTREMATA. ORDER BIMANA. 137 



principles of classification were not so well established as they 

 are at present. But it is now almost universally considered, 

 that the absence of the placenta, connected as it is with the low 

 development of the brain, and with other evidences of an inferior 

 grade, is a character of the most essential nature, completely 

 distinguishing the animals by which it is manifested, from any to 

 which they may bear a general resemblance in adaptive charac- 

 ters ( 25). And this can be hardly otherwise than true ; 

 since we find that the Marsupialia, taken as a group, have more 

 points of real agreement with each other, than any of them have 

 with animals of other orders. 



XII. MONOTREMATA, or animals with a single outlet ; a cha- 

 racter which has been already explained ( 117). This order is 

 very limited, containing only two genera ; which were formerly 

 placed among the Edentata, on account of the absence of teeth in 

 their jaws. They are altogether most remarkable animals ; and 

 present several points of the greatest interest both to the Physio- 

 logist and Zoologist, as do generally, indeed, those animals 

 which stand on the borders of two great divisions. 



ORDER I. BIMANA. 



127. The name Bimana is the most appropriate that could 

 be found for an order constituted by the human species only ; for 

 Man alone is two-handed. " That," says Cuvier, " which con- 

 stitutes the hand) properly so called, is the faculty of opposing 

 the thumb to the other fingers, so as to seize the most minute 

 objects, a faculty which is carried to its highest degree of per- 

 fection in Man, in whom the whole anterior extremity is free, 

 and can be employed in prehension." Some Naturalists refuse 

 the term hand to the extremities of the Monkey tribe, preferring 

 to call them graspers; for it is certainly true that, although most 

 of them possess an opposable thumb, yet they are destitute of the 

 power of performing many of those actions, which we regard as 

 most characteristic of the hand. These actions are dependent 

 upon the size and power of the thumb, which is much more de- 



