OF THE WOMliAT, KOALA, ANB PHALASTGERSi 885 



short peronei and an accessory quinti tendon detached from the 

 last for the first phalanx of the outer toe. In my specimen this 

 last slip is absent, but I believe it is represented by one of the 

 slips of the exhensor longus digitorum. 



Ruge pointed out that the eivtensor brevis digitorttm was 

 originally derived from the peroneal group of muscles. It is 

 present in all Marsupialia, but varies in the degree of development. 

 In Phalanger it runs to the four toes. In Phascolarctos it is 



Text-figure 41. 



E.L.R 



Extensors of foot in Phascolomi/s mitchelli (above) and Phascolarctos cinereus 



(below). 



E.L.D : extensor longus digitorum; E.L.P : extensor longus liallucis ; P: peronei; 



T.A : tibialis anticus. 



inserted into the two inner toes. And in both forms it arises 

 from the fibula. In Phccscolomys it arises fron the outer part of 

 the tarsus, and is inserted into the inner pair of toes. 



Tibialis Posticus : — This muscle has already been fully described 

 by Cunningham (2), Young (14), and Macalister (5, 18). In 

 Phascolomys it is a single muscle arising from the back of the tibia 

 and running to the inner part of the scaphoid. In Phascolarctos, 

 Phalanger, and Pseudochirus it is double. In the Koala two 

 fibular slips run to the scaphoid and entocuneiform ; but in the 

 Phalangers both tibial and fibular bellies run to the scaphoid. 



Phoc. Zool. Soc— 1922, No. LX. 60 



