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



of the metacarpal bone of the finger, which lies adjacent to that into which the muscle is 

 inserted. By this the muscle is enabled to act at a greater advantage, because its tendon 

 is prevented from clinging too closely to the base of the phalanx upon which it is acting. 

 A similar arrangement can be made out in the Thylacine, but here the bands are weak 

 in comparison with those found in the Cuscus. 



The dorsal interrossei muscles of the Cuscus are provided with the same accessory 

 slips in connection with their palmar surfaces as those we have already seen in the 

 Thylacine. They are not nearly so well developed, however, and they are differently 

 placed. The first is an adductor of the index ; the second abducts the middle finger to 

 the ulnar side of the hand ; and the third abducts the ring finger. They are attached 

 to the fingers with which they are associated in the same manner as in the Thylacine. 



Palmar group (fig. 3). — The muscles which compose this group are the same as 

 those in the two preceding animals, viz., (1) an adductor pollicis (h) ; (2) an adductor 

 minimi digiti (c) ; (3) an adductor indicis (a) ; (4) and an adductor of the ring finger (&). 



In man we see the adductor pollicis arising along the middle line of the hand from 

 the middle metacarpal bone. It adopts this origin in order that it may obtain a more 

 powerful action upon the thumb, and have a standpoint by means of which it may draw 

 the thumb more completely across the palm of the hand. In the Thylacine and 

 Phascogale there is also a tendency for the adductor muscles to seek the middle line of 

 the hand for their origins. They arise close to each other, and then radiate towards 

 their insertions. In the Cuscus all the adductors arise from the middle line, but in a 

 different manner from the adductor pollicis in man. A median fibrous raphe extends 

 downwards from the base of the metacarpal bone of the middle finger, and the adductors 

 arise from each side of this. Thus the adductor pollicis and adductor mimimi digiti 

 spring from the upper two-thirds of the raphe, the one opposite the other. They also 

 arise, however, by a few fibres from the front of the carpus. The adductors of the index 

 and ring fingers are very small, and take origin from the raphe below the preceding and 

 also opposite each other. A few fibres forming a fleshy fasciculus (a.b), in front of the 

 raphe, and in no way connected with it, pass round the base of the middle finger, and 

 are attached, on the one hand, to the adductor tendon of the ring finger, and, on the other, 

 to the adductor tendon of the index finger. It is an adductor of these fingers, but having 

 no intermediate attachment, it must act upon both fingers simultaneously. 



These muscles constitute with the raphe a thin stratum which hides from view the 

 greater number of the intermediate muscles. 



The intermediate group of muscles requires no special description. They agree in 

 all essential points with the same muscles in the Thylacine and Phascogale. Of the two 

 slips which compose the individual muscles it is somewhat curious to observe that 

 whereas one is always inserted directly into the phalanx, the other has both an attach- 

 ment to the phalanx and to the dorsal expansion of the extensor tendon. The flexor 



