MUSCLES ON THE DOBSAL SUBFACE OF THE FOBEABM. 395 



bones respectively (Fig. 352, p. 394). Each ends in a tendon which is directed 

 distally behind the deep transverse metacarpal ligament, to be inserted into the 

 dorsal expansion of the extensor tendon, the capsule of the metacarpo-phalangeal 

 articulation, and the side of the first phalanx of the finger ; the first is inserted 

 into the medial side of the second finger ; the second and third into the lateral sides 

 of the fourth and fifth fingers. The deep part of the flexor pollicis brevis (inter - 

 osseus primus volaris) is to be regarded as the homologous muscle of the first 

 interosseous space. 



Mm. Interossei Dorsales. The dorsal interossei are four in number. Each 

 arises by two heads from the sides of the metacarpal bones bounding each in- 

 terosseous space (Figs. 353, p. 394, and 354, p. 395). 



Each forms a fleshy mass, ending in a membranous tendon which, passing 

 distally, behind the deep transverse metacarpal ligament, is inserted exactly like 

 the volar muscles into the dorsal aspect of each of the four fingers. The insertion 

 of the first dorsal interosseous muscle is into the lateral side of the index finger ; 

 the second muscle is attached to the lateral side of the middle finger ; the third 



INSERTION OF FLEXOR 



CARPI ULNARIS 



ORIGINS OF 

 VOLAR INTER- 

 OSSEOUS MUSCLES 

 INSERTION OF 



OPPONENS DIGITI 

 QUINTI 



INSERTION OF 



- ABDUCTOR DIGITI 

 QUINTI 



ABDUCTOR POLLICIS BREVIS : origin (cut) 

 INSERTION OF FLEXOR CARPI RADIALIS 



INSERTION OF OPPONENS POLLICIS 



Lateral head of FIRST DORSAL 

 INTEROSSEOUS crossed by 

 INTEROSSECJS PRIMUS VOLARIS 



ABDUCTOR POLLICIS BREVIS : 

 insertion (cut) 



ADDUCTOR POLLICIS OBLIQUUS 

 (insertion) 



ADDUCTOR POLLICIS TRANSVERSUS 

 (insertion) 



FIRST DORSAL INTEROSSEOUS MUSCLE 

 SECOND DORSAL INTEROSSEOUS MUSCLE 

 THIRD DORSAL INTEROSSEOUS MUSCLE 

 FOURTH DORSAL INTEROSSEOUS MUSCLE 



FIG. 354. DORSAL INTEROSSEOUS MUSCLES OF THE HAND (seen from the Volar Aspect). 



muscle to the medial side of the same finger; and the fourth muscle to the medial 

 side of the ring finger. 



The interosseous muscles of the hand in some cases have a disposition similar to 

 that of the corresponding muscles of the foot (p. 435). 



Nerve-Supply. The deep branch of the ulnar nerve (C. 8. (T. 1.)). 



Actions. -The interossei muscles act in a similar way to, and along with, the lumbricales, 

 flexing the fingers at the metacarpo-phalangeal joints, and extending them at the inter- 

 phalangeal joints. In addition, the dorsal interossei serve to abduct the fingers into which they 

 are inserted (fore, middle, and ring fingers) from the middle line of the middle finger ; the volar 

 muscles on the other hand are adductors of the fingers into which they are inserted (fore, ring, 

 and little finger) towards the middle line of the middle finger. 



THE MUSCLES ON THE DORSAL SURFACE OF THE FOREARM. 



The group of muscles occupying the lateral side of the elbow and the dorsal 

 surface of the forearm and hand include the supinator muscles of the forearm and 

 the extensors of the wrist and digits. They are divisible into a superficial and a 

 deep layer. 



The superficial layer comprises seven muscles, which are in order, from the 

 radial to the ulnar side of the forearm, the brachioradialis, the two radial extensors 

 of the carpus, the extensor digitoruin communis and extensor digiti quinti proprius, 

 the extensor carpi ulnaris, and the anconseus. 



