170 UE. B. A. BEx\SLET ON THE EVOLUTION 



as pointed out by Dollo (1899), presents a more extreme type (third arboreal phase, p. 163), 

 the second and third digits being greatly reduced, and almost completly enclosed in a 

 common integument ; while the fourth digit is greatly enlarged, and like the fifth is 

 provided with a nail instead of a claw, as in the placental Primates. In addition to these 

 obviously progressive characters, Tarsipes presents certain other peculiarities. The 

 terminal pad of the hallux is not swollen to the same extent as is usual in arboreal forms. 

 The hallucal plantar pad is very short. The second digital plantar pad is subdivided and 

 its outer portion has migrated on to the base of the fourth digit. 



The larger forms Fetaurus {hreviceps) and DactijJopsila almost repeat the characters 

 of Dromicia. In the former there is an accessory hallucal pad as in Acrohates. 

 Dactylopsila differs only in that the claws are very powerful and the digits appear to be 

 jjermanently bent at the joints of the first and second phalanges. 



Among the species of Fhalanger we find in P. orientalis and P. lullul(B a slight 

 deviation from the general type. Except for a small area on the inner side of the 

 foot between the hallucal and the first digital pad, and another between the marginal 

 and the outer digital pad, the whole plantar surface is occupied by striations. This 

 condition is obviously the result of a fusion of the originally separate pads. The 

 hallucal pad is very broad, and its striations, which run in an oblique direction, join 

 posteriorly with those of the marginal pad. The striations of the digital pads cross from 

 one to the other, and, in the case of the second and third, they also extend backwards 

 on the sole to meet those of the hallucal and marginal pads. The halhix is set rather 

 further back than in Dromicia, so that its opposability is more perfect. 



In Trichosurus the extension of the plantar striations is not indicated. The hallucal 

 pad is well developed, but is not sharply differentiated from the sole on the outer side- 

 Its striations are very short. The digital pads are oval and well separated from one 

 another. The marginal pad shows much the same characters as the hallucal one. At 

 first sight the non-extension of the plantar pads appears to represent a distinction 

 between this form and Fhalancjer; but in P . celehensis we find much the same condition 

 as in Trichosurus, showing that the condition in the above-described species of Fhalanger 

 is a special one. 



In the structure of the pes there is no such difference between the phascolarctine and 

 phalangerine groups as is observable in dentition. The foot of 'Pseadochirus {Forbesi) 

 conforms to the type in Dromicia. The first and second digital pads are closely set 

 together and have their striations concentrically arranged. The conditions in Phas- 

 colarctus give no indication of special relationship with Pseudochirus. The general 

 conformation of the digits is the same, but the plantar pads have all been reduced, the 

 sole being uniformly covered with a soft granulated skin somewhat as in Sarcophilus 

 and Phascolomys. The hallux is, however, set back to a much greater extent than 

 in Pse^idochirus, so that it is more perfectly opposable. AVith only a slightly greater 

 displacement, its axis would be in the same line as that of the fourth digit which it 

 opposes. 



