

FOREARM AND HAND 147 



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 first or most lateral dorsal interosseous muscle^ this 

 tendon is inserted into the lateral side of the base of the first 

 phalanx, and also into the lateral margin of the dorsal expansion 

 of the extensor tendon of the index. The second and third 

 dorsal interosseous muscles are inserted in a similar manner upon 

 either side of the base of the first phalanx of the middle finger ; 

 whilst \hefourth has a corresponding insertion upon the medial 

 aspect of the base of the first phalanx of the ring finger. 



The first dorsal interosseous muscle is frequently termed 

 the abductor indicis, and between its two heads of origin the 

 radial artery enters the palm. Between the heads of the other 

 three muscles the small perforating arteries pass. 



The three mm. interossei volares can only be seen 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 there- 

 fore 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 palmar 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 palmar interosseous muscle takes origin from the 

 metacarpal bone, and presents a corresponding insertion into 

 the lateral side of the first phalanx and extensor expansion 

 of the little finger. The interosseous muscles are supplied by 

 the profunda branch of the ulnar nerve. 



Deep Head of M. Flexor Pollicis Brevis. This small muscle, 

 which is also known as the m. interosseous primus volaris (Henle), can 

 best be displayed from the dorsal aspect of the hand by reflecting the 

 lateral head of the first dorsal interosseous muscle. It arises from the 

 base of the metacarpal bone of the thumb, and is inserted into the medial 

 sesamoid bone of that digit. It is deeply placed, and is entirely covered, 

 on its volar aspect, by the oblique part of the adductor pollicis. 



Tendon of the Flexor Carpi Radialis. The tendon of this 

 muscle should now be traced through the groove on the volar 

 aspect of the os multangulum majus to its insertion into the 

 base of the metacarpal bone of the index. It presents also a 

 minor attachment to the base of the middle metacarpal bone. 



