330 THE MUSCULAR SYSTEM. 
THE INTEROSSEOUS MUSCLES. 
The interosseous muscles of the hand are arranged in two sets, palmar and 
dorsal. 
The palmar interossei (1m. interossei volares) are three in number, occupying 
the three inner interosseous spaces. 
Each arises by a single head; the 
jirst from the ulnar side of the shaft 
of the second metacarpal bone; the 
second and third from the radial 
sides of the shafts of the fourth and 
» | fifth metacarpal bones respectively. 
fe «| Each ends in a tendon which is 
oe directed downwards behind the deep 
Co transverse metacarpal ligament, to 
be inserted into the dorsal expansion 
of the extensor tendon, the capsule 
of the metacarpo-phalangeal articu- 
lation, and the side of the first 
phalanx of the fingers; the jirst is 
inserted into the ulnar side of the 
second finger; the second and third 
into the radial side of the fourth and 
. p fifth fingers. 
eel The dorsal interossei are four 
in number. Each arises by two 
heads from the sides of the meta- 
carpal bones bounding each inter- 
osseous space. Each forms a fleshy 
mass, and ends in a membranous tendon, which, passing downwards behind the 
transverse metacarpal ligament, is inserted exactly like the palmar muscles into the 
dorsal aspect of each of the four fingers. The insertion of the jivs¢ dorsal inter- 
Fic. 245.—THE PaLtMar INTEROSSEOUS MUSCLES. 
P!, first ; P2, second ; and P®, third palmar interosseous 
muscles. 
ABDUCTOR POLLICIS: origin (cut) 
INSERTION OF FLEXOR 
INSERTION OF FLEXOR CARPI RADIALIS CARPI ULNARIS 
ORIGINS OF 
PALMAR INTER- 
OSSEOUS MUSCLES 
INSERTION OF 
OPPONENS MINIMI 
DIGITI 
INSERTION OF OPPONENS POLLICIS 
INTEROSSEUS PRIMUS VOLARIS 
ABDUCTOR POLLICIS: insertion (cut 
INSERTION OF 
ABDUCTOR MINIMI 
DIGITI 
ts : Nee 
ADDUCTOR OBLIQUUS (insertion) | 
ADDUCTOR TRANSVERSUS (insertion)- | 
FIRST DORSAL INTEROSSEOUS MUSCLI-7— 
SECOND DORSAL INTEROSSEOUS MUSCLE— 
THIRD DORSAL INTEROSSEOUS MUSCLE 
FOURTH DORSAL INTEROSSEOUS MUSCLE 
Fia, 246.—Dorsat INrEROSSEOUS MUSCLES OF THE HAND (seen from the Palmar Aspect). 
osseous muscle is into the radial side of the index finger; the second muscle is 
attached to the radial side of the third finger; the finds maneele to the ulnar side 
of the same finger; and the fowrth muscle ‘to the ulnar side of the fourth finger. 
These muscles fill up the interosseous spaces; the dorsal interossei are visible 
on the back of the hand when the extensor tendons are removed; in the palm the 
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