BY WILLIAM A. HARWELL, M.A., B.SC. 179 



As usual in the Marsupialia the supinator longus is a powerful 

 muscle ; as in Phalangista and Cuscus it is inserted into the 

 scaphoid. 



Both radial extensors are developed in all the three genera under 

 consideration (1). In the Cuscus Cunningham describes the extensor 

 carpi radialis brevior as having three heads of origin, one from 

 the outer condyle, a second from the tendinous expansion over 

 the supinator brevis and a third from the posterior border of the 

 radius in its proximal part. In Petaurista the muscle has a similar 

 origin but derives none of its fibres directly from the radius. 



The supinator mantis {extensor ossis metacarpi pollicis) in all 

 three genera is inserted into the trapezium as well as into the base 

 of the metacarpal of the pollex. 



The arrangement of the extensors of the digits of the manus is 

 the same in Petaurista as in Phalangista and Cuscus. The extensor 

 sublimis arising from the outer condyle as usual gives off tendons 

 to the four ulnar digits. The extensor profundus, arising from the 

 ulna, is composed of two parts ; the extensor secundi internodii 

 polUds and the extensor medii ; the latter is connected with the second 

 and fourth toes as well as with the middle. Besides these there 

 is an extensor minimi digiti which arises from the outer condyle 

 and represents an extensor secundus. (2) 



The extensor carpi ulnaris consists in Petaurista, as in Phalan- 

 gista and Cuscus, of a single muscle. 



In none of the three genera has the pronator radii teres a 

 coronoid head of origin. This seems to be universally the case 

 in Marsupials. (3) 



Thejlexor carpi radialis in Petaurista and Phalangista is inserted, 

 as in Cuscus into both the second and third metacarpals. 



(1) Macalister describes a single radial extensor in the Phalanger as in 

 Macropus, Phascolomys and Sarcophilus. 



(2) Humphrey. " Observations on Myology." p. 185. 



(3) Macalister. " On the Myology of the Wombat and Tasmanian Devil." 

 Ann. Mag. Nat. Hist., 4th series Vol. V., p. 1. Young, "On the Muscular 

 Anatomy of the Koala," Journ. Anat. Phys,, Vol. XVI., p. 228. 



