408 THE MUSCLES AND FASCIAE. 



13. Middle Palmar Region. 



Lumbricales. Interossei dorsales. 



Interossei palmares. 



The Lumbricales (Fig. 243) are four small fleshy fasciculi, accessories to the 

 deep Flexor muscle. They arise from the, tendons of the deep Flexor : the first and 

 second, from the radial side and palmar surface of the tendons of the index and 

 middle fingers respectively ; the third, from the contiguous sides of the tendons of 

 the middle and ring fingers ; and the fourth, from the contiguous sides of the 

 tendons of the ring and little fingers. They pass to the radial side of the corre- 

 sponding fingers, and opposite the metacarpo-phalangeal articulation each tendon is 

 inserted into the tendinous expansion of the Extensor communis digitorum, 

 covering the dorsal aspect of each finger. 



The Interossei muscles (Figs. 244, 245) are so named from occupying the 

 intervals between the metacarpal bones, and are divided into two sets, a dorsal 

 and palmar. 



The Dorsal interossei are four in number, larger than the palmar, and occupy 

 the intervals between the metacarpal bones. They are bipenniform muscles, aris- 

 ing by two heads from the adjacent sides of the metacarpal bones, but more exten- 

 sively from the metacarpal bone of the finger into which the muscle is inserted. 

 They are inserted into the bases of the first phalanges and into the aponeurosis of 

 the common Extensor tendon. Between the double origin of each of these mus- 

 cles is a narrow triangular interval, through the first of which passes the radial 

 artery ; through the other three passes a perforating branch from the deep palmar 

 arch. 



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 inserted 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. 

 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 

 inserted into the same side of the first phalanx 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 Abductor muscle takes the place 

 of one of the pair. 



Nerves. The two outer Lumbricales are supplied by the sixth cervical nerve, 

 through the third and fourth digital branches of the median nerve : the two 

 inner Lumbricales and all the Interossei are supplied by the eighth cervical 

 nerve, through the deep palmar branch of the ulnar nerve. Brooks states that 

 the third lumbrical received a twig from the median in twelve out of twenty-one 

 cases. 



Actions. The Palmar interossei muscles adduct the fingers to an imaginary 

 line drawn longitudinally through the centre of the middle finger ; and the Dorsal 

 interossei abduct the fingers from that line. In addition to this, the Interossei, in 



