14 THE VOYAGE OF H.M.S. CHALLENGER. 



In the Cuscus (PL II. fig. 5, s.l.) and Phascogale the supinator longus is a muscle of 

 great size, relatively much larger than the same muscle in man. It springs from the upper 

 two-thirds of the external supracondyloid ridge of the humerus. Its tendon proceeds in 

 a groove upon the dorsal aspect of the lower end of the radius, under cover of the posterior 

 annular ligament to the scaphoid bone, into the outer aspect of which it is inserted. 



Macalister 1 mentions that the supinator longus is absent in the Tasmanian Devil ; 

 with this single exception it appears to be almost universally present in the Marsupialia, 

 and in the case of the Koala it attains a very great magnitude. 2 



Radial extensors. — The fleshy bellies of the extensor carpi radialis longior and 

 extensor carpi radialis brevior are completely amalgamated in the Phascogale; the tendons, 

 however, are separate. This also was the case in the female Thylacine. but in the large 

 male Thylacine (PL I. fig. 5, c.l. and c.b.) and in the Cuscus the two muscles were 

 separate throughout their entire extent. 



In the Thylacine and Phascogale the radial extensors arise from the external 

 supracondyloid ridge of the humerus below the supinator longus, and they are respectively 

 inserted into base of the second and third metacarpal bone on its dorsal aspect. 



The extensor carpi radialis brevior in the Cuscus (PL II. fig. 5, c.b.) is a very large 

 and powerful muscle, and its origin is somewhat complicated. It may be said to arise 

 by three distinct heads — (1) from the upper part of the external condyle of the humerus 

 (c.b 1 .) ; (2) from the tendinous expansion on the surface of the supinator brevis (c.b 2 .) ; 

 (3) from the posterior border of the radius below the supinator brevis (c.b 3 .). These 

 three slips of origin unite to form the muscle, which is inserted. as usual into the radial 

 border of the shaft of the metacarpal bone of the medius a short distance beyond the base. 



The extensor carpi radialis longior in the Cuscus (c.l.) presents the ordinary origin, 

 from the lower third of the external supracondyloid ridge of the humerus, and it is 

 inserted into the radial border of the shaft of the metacarpal bone of the index about its 

 middle. 



As a general rule, in the Marsupials the radial extensors are amalgamated, and even 

 in those cases where they are separate they exhibit, as in the Thylacine, a tendency to 

 fusion. Thus Young 2 states that in the three specimens of Koala which he examined 

 one possessed a single radial extensor, whilst in the other two they were " separate and 

 distinct." Again, Meckel, 2 in his work upon Comparative Anatomy, states that in the 

 Opossum there are two radial extensors, whilst Macalister 3 describes only one. The 

 peculiar triple origin of the extensor carpi radialis brevior which is noticed in the Cuscus 

 has not been observed (so far as I am aware) in any other Marsupial. 



Extensor communis digitorum. — In all three animals this is a comparatively small 

 muscle. It springs from the outer aspect of the external condyle. 



1 Ami. and Mag. of Nat. Hist., vol. x., 4th series. 2 Young, Jour. Anat. and Phys., vol. xvi. 



3 Annals and Magazine of Natural History, vol. v. 



