146 THE UPPER EXTREMITY 



The tendon of the extensor digiti quinti proprius splits into two 

 parts. Of these the lateral joins the tendon of the common 

 extensor which goes to that digit, whilst the medial ends in the 

 dorsal expansion. 



Nervus Interosseous Dorsalis (O.T. Posterior Interosseous 

 Nerve). The terminal filament of this nerve can now be 

 traced distally to the dorsal aspect of the carpus. It passes 

 under cover of the extensor indicis proprius, the tendons of 

 the extensor communis, and the dorsal carpal ligament. On 

 the carpus it ends in a gangliform swelling, from which fine 

 twigs proceed for the supply of the numerous joints in the 

 vicinity. 



Dissection. The limb should now be turned round, so that the trans- 

 verse metacarpal ligament which stretches across the volar surface of the 

 heads of the metacarpal bones may be examined previous to the dissection 

 of the interosseous muscles. 



Transverse Metacarpal Ligament. The transverse liga- 

 ment of the head of the metacarpal bones is a strong band 

 composed of transverse fibres, which is placed upon the volar 

 aspect of the heads of the four metacarpal bones of the fingers. 

 Commencing on the lateral side upon the distal extremity of 

 the index metacarpal, it ends at the medial margin of the 

 hand upon the head of the metacarpal bone of the little finger. 

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

 powerful accessory volar ligaments of the four medial 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 must also be divided in 

 the intervals between the fingers. 



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 mm. interossei dorsales are four in number, and are 

 more powerful than the volar muscles. They are best 

 seen on the dorsal aspect of the hand, but they are also 

 visible in the palm. They act as abductors of the fingers 

 from the central line of the middle digit, and their in- 

 sertions are arranged in accordance with this action. Each 



