342 ON THE MARSUPIAL QUADRUPEDS 



purely vegetable diet ; but their true molars are differently 

 formed, and the second even departs from this type of denti- 

 tion, by having only two incisors in the upper as well as in 

 the under jaw. 



This form of dentition is common to the genera Phalangis- 

 ta, Petaurus, Phascolarctos, Macropus, and Hypsiprymnus. 



The next organs to be considered as influencing the habits 

 and economy of the marsupials, are the extremities. I have 

 already observed how wofully these organs have been neg- 

 lected by the makers of systems ; though it is difficult to con- 

 ceive how scientific zoologists could possibly undervalue or 

 overlook the instruments of the most important and striking 

 actions of animal life. Not only do the great function of lo- 

 comotion, and its thousand varieties and adaptations, whether 

 to aquatic, arboreal, terrestrial, or aerial habits, depend solely 

 and entirely upon the extremities ; but the scarcely less im- 

 portant functions of prehension, manipulation, 1 burrowing, 

 and even the sense of touch, the source of our most excellent 

 ideas, and the index of intellectual power, reside in the same 

 organs. The formation and modifications of the extremities, 

 therefore, do not furnish those merely second-rate characters, 

 which should justify the philosophical zoologist in postpon- 

 ing them to slight modifications of dentition, or neglecting 

 them altogether. On the contrary, as every action and habit 

 of animal life, except the mere appetite, depend upon these 

 organs ; as they are the most extensively influential, so their 

 modifications should hold the most prominent place in every 

 system, and will be invariably found to lead to the most na- 

 tural and philosophical arrangements. 



The marsupial quadrupeds, always excluding the Mono- 

 tremata, which cannot be properly compared with other 

 mammals, present four very distinct and primary influential 

 modifications of the extremities. 



1. The Pedimanous form, where the fingers are long, se- 

 parate and prehensile, and the hind thumb opposable to the 

 other toes. The animals consequently possess perfect pow- 

 ers of prehension and manipulation ; they are entirely arbo- 

 real, feed indifferently upon vegetable and animal substances, 

 though preferring the former, and all have a c<ecum of mode- 

 rate dimensions. This family, which I shall denominate 

 Cheirogrades, 7 - from their locomotion being performed by 



1 1 use this term as synonymous with the common word, handling. 

 2 In the paper as originally written, these families were called respectively 

 Scansores, Cursores, Saltatores, and Fossores : I have now substituted the 

 names in the text, as more pliant when used adjectively, as in speaking of 

 saltigrade or digitigvade marsupials, &c. April, 1839. 



