REPORT ON THE MARSUPIALIA. 21 



Intermediate group. — The muscles which constitute this group are five in number, 

 and are placed one over the palmar aspect of each metacarpal hone. That in relation to 

 the metacarpal bone of the thumb is the flexor brevis pollicis, and that lying upon the 

 metacarpal bone of the little finger is the flexor brevis minimi digiti. But further, each 

 muscle consists of two slips, which in the case of the short flexors of the thumb and little 

 finger, remain distinct and separate from each other throughout, whilst in the case of the 

 other three they arise by a common tendon, and only separate the one from the other at 

 a point corresponding to the middle of the metacarpal bones. The dorsal interossei are 

 in no way connected with these muscles. 



Flexor brevis minimi digiti. — This muscle is not so strongly marked as the short 

 flexor of the thumb. Its ulnar head arises from the unciform bone, and from the annular 

 ligament, whilst its radial portion takes origin from the carpus somewhat deeper. They 

 extend downwards side by side, and are inserted one into each side of the base of the 

 first phalanx of the little finger. 



Flexor brevis pollicis. — The two slips of this muscle arise close together, from the 

 second row of carpal bones, and are inserted one into each side of the base of the first 

 phalanx of the thumb. 



The three remaining muscles of this group (viz., those which correspond to the index, 

 middle, and ring fingers) arise partly from the base of the metacarpal bone with which 

 each is associated, and partly from the ligamentous bands on the palmar aspect of the 

 carpus. Half-way down the metacarpus each muscle divides into two slips, and these 

 are continued downwards so as to embrace the base of the first phalanx of the finger 

 with which they are connected. Here the slips end in debcate tendons, which are 

 inserted one into each side of the phalangeal base, partly into bone and partly into the 

 extensor tendon. 



These muscles lie in series with the short flexors of the thumb and little finger, and 

 only differ from them in having each a single origin, and in being inserted in part into 

 the dorsal extensor expansion. Moreover, their attachments indicate a correspondence 

 of action. When the two slips of each muscle act in unison, they must flex the fingers 

 at the metacarpophalangeal joints ; when they act separately and independently of each 

 other, the action must be one of abduction or adduction, according to the slip employed, 

 and this latter action must be performed most effectively by those muscles connected 

 with the thumb and little finger, inasmuch as their slips are distinct from each other 

 throughout, and not in any way hampered by the common origin of the others. The 

 insertion of those muscles connected with the index, middle, and ring fingers into the 

 extensor tendon, allows them to take a part in extending the fingers — a privilege which 

 the flexor brevis pollicis and flexor brevis minimi digiti from their purely phalangeal 

 insertions do not enjoy. 



