FOREARM AND HAND 193 



It is not directly attached to the bones, but is fixed to the 

 powerful volar accessory ligaments of the medial four metacarpo- 

 phalangeal joints, and it effectually prevents excessive separation 

 of the metacarpal bones from each other. 



Dissection. To obtain a satisfactory view of the interosseous 

 muscles, the transverse part of the adductor pollicis, if not 

 previously reflected, should be detached from its origin, and 

 thrown laterally towards its insertion into the thumb. The 

 transverse metacarpal ligament also must be divided in the 

 intervals between the fingers. Then the palmar and dorsal 

 interossei must be cleaned and their limits must be defined. As 

 the fascia is cleaned from their surfaces the margins of the 

 muscles become evident. There is one dorsal interosseous 

 muscle in each intermetacarpal space, and in the medial three 

 spaces there is also a volar interosseous muscle. 



Mm. Interossei. The interosseous muscles occupy the 

 intervals between the metacarpal bones. They are seven 

 in number, and are arranged in two groups, viz. a dorsal 

 and a volar. 



The three volar interossei can be seen only on the palmar 

 aspect of the hand. They act as adductors of the index, 

 ring, and little fingers towards the middle digit, and each 

 muscle is placed upon the metacarpal bone of the finger upon 

 which it acts. The first volar interosseous muscle therefore 

 arises from the metacarpal bone of the index finger, and 

 its delicate tendon is inserted upon the medial side of that 

 digit, partly into the base of the first phalanx, and partly 

 into the extensor expansion. The second volar interosseous 

 muscle springs from the metacarpal bone of the ring finger, 

 and has a similar insertion into the lateral side of that digit. 

 The third volar interosseous muscle takes origin from the 

 metacarpal bone of the little finger, and is inserted into the 

 lateral side of the first phalanx and the extensor expansion 

 of that finger. 



The dorsal interossei are four in number, and are larger 

 than the volar muscles. They are seen best on the dorsal 

 aspect of the hand, but they are visible in the palm also. 

 They act as abductors of the fingers from the central line 

 of the middle digit, and their insertions are arranged in 

 accordance with that action. Each muscle arises by two 

 heads from the contiguous surfaces of the two metacarpal 

 bones between which it lies, and the fibres converge in a 

 pennate manner upon a delicate tendon. In the case of the 



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