THE ANATOMY OF THE CHIMPANZEE. 39 



Abductor pollicis longus to trapezium and sesamoid bone. 



Exten>ior nrlml iiitevnod'il nollic'o^ is so fused with the preceding as to su'j-o-est 

 one muscle with two tendons; it is inserted into tlie base of the first metacarpal on the 

 radial side (better called extensor pollicis brevis). 



Extensor secundi internodil poll'icU, vel extensor jJoUieis longus, I'uns from the 

 lower part of the ulna and interosseous membrane into a fibrous expansion over the back 

 of the thumb, and is inserted into the second phalanx. 



Extensor propr'ius hidicis is a small muscle going to the index only; in 

 Hepburn's chimpanzee it sent a slip to the ring finger. 



Interossei manus. There are four dorsal, practically the same as in man. There 

 are seven palmar; namely, two for the index, the middle and ring fingers, respectively, 

 and one for the little finger. The smallest of these is the first. It arises from the 

 radial side of the metacarpal bone of the index internal to the belly of the dorsal. The 

 second is a large one on the ulnar side of the index. The third and fourth lie on the 

 metacarpal of the middle finger, touching each other and arising in part from a fibrous 

 septum between them. The third receives also a few fibers from the base of the second 

 metacarpal. The fifth and sixth arise (excepting for the last detail) in a similar manner 

 from the fourth metacarpal. The seventh arises from the radial side of tlie fifth 

 metacarpal and from the hook of the unciform. 



There is (with one exception) an important difference between the insertion of the 

 dorsal and palmar interossei. The dorsal are attached to the sides of the bases of the 

 first phalanges, still the chief action is to flex them ; lateral movement is not great. 

 The palmar ones end in well-defined tendons which run along the sides of the first 

 phalanges and end in the fibrous expansion over their dorsal aspects. Their chief 

 action is to flex the first phalanges and extend the second and third. The excep- 

 tion alluded to is the first palmar which has a very small tendon more or less fused 

 with that of the first dorsal. 



The chimpanzee has been described as having six palmar interossei, my little 

 first one not having, I believe, been hitherto observed. I have called it a palmar 

 interosseous because it seems to me a distinct uiuscle; still its mode of termination 

 gives support to those who would call it a part of the first dorsal. For the others 

 not found in man I cannot admit this interpretation. They are all in the same 

 plane and have a similar insertion. Compare Hepburn on anthropoids, Cunningham 

 on Thylacine (Journ. aiiat. physiol., vol. 12), and Champneys on chimpanzee (ibid., 

 vol. 6). 



