320 



SURGICAL ANATOMY. 



Fig. 179. The Palmar Interossei of Left Hand. 



triangular in form, and arises by two heads, separated by a fibrous arch, for the 

 passage of the radial artery into the deep part of 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 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 are inserted into the middle finger, the former into its 

 radial, the latter into its ulnar side. The fourth is inserted in 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. 



They arise from the entire length of the 

 metacarpal 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 in- 

 serted 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 In- 

 terossei muscles, with the exception of the 

 little finger. 



Nerves. The two outer Lumbricales 

 are supplied by the median nerve ; the 

 rest of the muscles of this group, by the 

 ulnar. 



Actions. The Dorsal interossei muscles 



abduct the fingers from an imaginary line drawn longitudinally through the centre 

 of the middle finger ; and the Palmar interossei adduct the fingers towards the 

 same line. . They usually assist the Extensor muscles ; but when the fingers are 

 slightly bent, they assist in flexing the fingers. 



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 ; the causes of displacement are thus easily recognized, and a suitable treatment in each 

 case may be readily adopted. 



In considering the actions of the various muscles upon fractures of the upper extremity, the 

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



Fracture of the clavicle is an exceedingly common accident, and is usually caused by indirect 

 violence, as a fall upon the shoulder ; it occasionally, however, occurs from direct force. Its most 

 usual situation is just external to the centre of the bone, but it may occur at the sternal or acro- 

 mial ends. 



Fracture of the middle of the clavicle (fig. 180) is always attended with considerable displace- 

 ment, the outer fragment being drawn downwards, forwards, and inwards ; the inner fragment 

 slightly upwards. The outer fragment is drawn down by the weight of the arm, and the action 

 of the Deltoid, and forwards and inwards by the Pectoralis minor and Subclavius muscles ; the 

 inner fragment is slightly raised by the Sterno-cleido-mastoid, but only to a very limited extent, 

 as the attachment of the costo-clavicular ligament and Pectoralis major below and in front would 

 prevent any very great displacement upwards. The causes of displacement having been ascer- 

 tained, it is easy to apply the appropriate treatment. The outer fragment is to be drawn out- 



