398 



MUSCLES AND FASCIA. 



The First Dorsal Interosseous muscle, or Abductor Indicis, is larger than the 

 others. It is flat, triangular in form, and arises by two heads, separated by a 

 fibrous arch, for the passage of the radial artery from the dorsum to the palm 

 of the hand. The outer head arises from the upper half of the ulnar border of 

 the first metacarpal bone ; the inner head, from almost the entire length of the 

 radial border of the second metacarpal bone ; the tendon is inserted into the 

 radial side of the index finger. The second and third dorsal interossei are in- 

 serted into the middle finger, the former into its radial, the latter into its ulnar 

 side. The fourth is inserted into the ulnar side of the ring finger. 



The Palmar Interossei, three in number, are smaller than the Dorsal, and 

 placed upon the palmar surface of the metacarpal bones, rather than between 



them. Thev arise from the entire length of the 

 Fig. 246.-The^m^ Interossei metacarpa i bone of one finger, and are inserted 



into the side of the base of the first phalanx and 

 aponeurotic expansion of the common Extensor 

 tendon of the same finger. 



The first arises from the ulnar side of the 

 second metacarpal bone, and is inserted into the 

 same side of the index finger. The second arises 

 from the radial side of the fourth metacarpal 

 bone, and is inserted into the same side of the 

 ring finger. The third arises from the radial 

 side of the fifth metacarpal bone, and is inserted 

 into the same side of the little finger. From 

 this account it may be seen, that each finger is 

 provided with two Interossei muscles, with the 

 exception of the little finger, in which the Ab- 

 ductor muscle takes the place of one of the 

 pair. 



Nerves. The two outer Lumbricales are sup- 

 plied by the median nerve ; the rest of the mus- 

 cles of this group, by the ulnar. 



Actions. The Dorsal Interossei muscles ab- 

 duct the fingers from an imaginary line drawn 

 longitudinally through the centre of the middle 

 finger ; and the Palmar Interossei adduct the 

 fingers towards that line. They usually assist the extensor muscles; but 

 when the fingers are slightly bent, they assist in flexing them. 1 



SUEGICAL ANATOMY. 



The student, having completed the dissection of the muscles of the upper extremity, should 

 consider the effects likely to be produced by the action of the various muscles in fracture of the 

 bones. 



In considering the actions of the various muscles upon Fractures of the Upper Extremity, I 

 have selected the most common forms of injury, both for illustration and description. 



1 M. Duchenne gives a different account of the mechanism of the extension of the fingers 

 and of the action of the interossei muscles from that usually accepted. According to him, the 

 extensor communis digitorum acts almost entirely on the first phalanges, extension of the 

 second and third phalanges being effected by the interossei muscles, which also act to a certain 

 extent as flexors of the first phalanges. This action of the interossei is additional to their 

 action in abduction and adduction (" Physiologic des Mouvements," pp. 261-298). M. Du- 

 chenne's view of the action of these muscles certainly derives support from the phenomena 

 observed in lead-palsy and from the results of galvanizing the common extensor and the inter- 

 ossei, as Dr. W. Ogle has been kind enough to point out to me. Thus also in a case related by 

 Mr. Hutchinson, in which the ulnar nerve had been divided below the part from which the ex- 

 tensor communis was supplied (and therefore the interossei were paralyzed while the extensor 

 acted), " the first phalanges were bent backwards on the metacarpal bones" (extended) " while 

 the fingers were curved into the palm" (second and third phalanges flexed). London Hospital 

 Reports, vol. iii. p. 307. 



