328 THE MUSCULAR SYSTEM. 
are concealed by the tendons of the flexor sublimis digitorum. On the finger each 
tendon is placed at first beneath, and afterwards upon, the tendon of the flexor 
sublimis digitorum, in its passage through the digital sheath. The lumbrical 
muscles passing downwards on the radial side of the deep flexor tendons lie beneath 
the digital vessels and nerves on their way to their insertion. 
The flexor longus pollicis arises from the anterior surface of the radius in its 
middle two-fourths, and from a corresponding portion of the interosseous mem- 
brane. Its radial origin is limited above by the oblique line and the origin of the 
flexor sublimis digitorum, and below by the insertion of the pronator quadratus 
muscle. The muscle ends above the wrist in a tendon, which passes into the 
hand beneath the anterior annular ligament, enveloped in a special synovial sheath. 
In the palm the tendon is directed downwards along the inner side of the thenar 
eminence, between the flexor brevis and adductor muscles of the thumb, to be 
inserted into the terminal phalanx of the thumb. 
In the forearm the muscle is deeply placed beneath the flexor sublimis 
digitorum. The radial artery lies upon it, and the anterior interosseous artery and 
nerve intervene between it and the flexor profundus digitorum. It crosses over 
the insertion of the pronator quadratus near the wrist. 
The pronator quadratus is a quadrilateral muscle, occupying the lower fourth 
of the forearm. It arises from the lower fourth of the anterior border and surface 
of the ulna, and is directed outwards to be inserted into the lower fourth of the 
anterior surface of the radius. 
The muscle is deeply placed beneath the flexor tendons, the radial and ulnar 
arteries, and the ulnar and median nerves. It conceals the lower part of the inter- 
osseous Membrane, the radius and ulna, and the anterior interosseous artery and 
nerve, which pass behind its upper border. The pronator quadratus is subject to 
considerable variations. It may even be absent; or it may have an origin from 
radius or ulna, or from both bones, and an insertion into the carpus. 
SHORT MUSCLES OF THE HAND. 
MUSCLES OF THE THUMB. 
The abductor pollicis (m. abductor pollicis brevis) arises from the anterior 
annular ligament and the ridge of the trapezium. Strap-like in form, it is inserted 
Transverse metacarpal 
ligament FIRST DORSAL 
INTEROSSEOUS MUSCLE 
INTEROSSEOUS MUSCLE 7 
FLEXOR LONGUS POLLICIS 
TENDON 
ADDUCTOR TRANSVERSUS 
POLLICIS 
ABDUCTOR AND FLEXOR 
BREVIS MINIMI DIGITI (cut) 
INTEROSSEOUS MUSCLE —4—ABDUCTOR POLLICIS (cut) 
INTEROSSEOUS MUSCLE FLEXOR BREVIS POLLICIS 
Deep palmar arch (along with deep 
branch of ulnar nerve) 
OPPONENS MINIMI DIGITI 
Median nerve (muscular branches) 
w 
/——ABDUCTOR POLLICIS (cut) 
o 
FLEXOR CARPI ULNARIS——~ y 
at / 
\ fi 7— EXTENSOR OSSIS METACARPI POLLICIS 
// 
Ulnar nerve—— FLEXOR CARPI RADIALIS TENDON 
| 
[ 
} \ 
Fic. 244.—SHort Muscles OF THE HAND. 
into the outer side of the first phalanx of the thumb and the capsule of the meta- 
carpo-phalangeal joint. 
ey sane ‘2 
EA LG AS: 
Sain? Balers 
} 
| 
