324 THE MUSCULAR SYSTEM. 
pronator radii teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and 
flexor sublimis digitorum. 
The pronator radii teres (m. pronator teres) 1s the most external and 
shortest muscle of this group. It has a double origin: (1) a superficial head, the 
‘ main origin, from the common 
tendon from the internal con- 
dyle of the humerus, from the 
fascia over it, and from an 
intermuscular septum between 
it and the flexor carpi radi- 
alis; (2) a deep head, a slender 
slip from the inner side of the 
coronoid process of the ulna, 
which joins the superficial 
origin of the muscle on its 
deep surface. The median 
nerve separates the two heads 
from one another. The mus- 
cle is directed downwards and 
outwards to be inserted into 
an oval impression on the 
Fic. 240.—SkEcTION ACROSS THE FOREARM IN THE MIDDLE middle of the outer surface of 
THIRD. the radius. 
A, PRONATOR RADII TERES (insertion); B, FLEXOR CARPI RADIALIS; C, The muscle forms the inner 
‘LEX SUBLIMIS sITORUM; D, PALMARIS LONGUS; E, FLEXOR CARPI rn ® 
ET EIESSO) STOO MEE MELAS AOE : Nee) boundary of the hollow of the 
ULNARIS; F, FLEXOR PROFUNDUS DIGITORUM; G, EXTENSOR CARPI 
ULNARIS; H, EXTENSOR LONGUS POLLICIS; I, EXTENSOR COMMUNIS elbow. It 18 superficially 
DIGITORUM; J, EXTENSOR OSSIS METACARPI POLLICIS ; K, ExTEensoR placed, except near its in- 
nas RADIALIS BHEVION ; os BATENSOE wus BADEAUIS Ron erOe ye sertion, where it is covered by 
RACHIO-RADIALIS. d@, Radius; b, Interosseous membrane; c, Ulna. 2 eae 
1, Radial nerve; 2, Radial Artery ; 3, Anterior interosseous artery ; the brachio-radialis muscle and 
4, Anterior pobenosscQus nerve (underneath flexor longus pollicis) ; by the radial vessels and nerve. 
5, Median, peryes a Ulnar artery 57 Viner BeLve ; 8, Posterior inter- The flexor carpi radialis is on 
osseous artery ; 9, Posterior interosseous nerve. 
its inner side. The muscle. 
conceals the ulnar and radial origins of the flexor sublimis digitorum, and the 
median nerve and ulnar artery, which are separated from one another by the deep 
head of origin. 
The flexor carpi radialis muscle has a single origin from the common 
tendon from the internal condyle, from the fascia over it, and from the inter- 
muscular septa on either side. Its fleshy belly gives place to a strong round 
tendon in the lower half of the forearm, which, at the wrist, enters the hand ina 
special compartment beneath the anterior annular ligament, and after occupying 
the groove on the trapezium, is inserted into the upper ends of the second and- 
third metacarpal bones on their anterior surfaces. 
The flexor carpi radialis is superficial except near its insertion. Its fleshy 
belly in the upper half of the arm hes between the pronator radii teres and the 
palmaris longus, and conceals the flexor sublimis digitorum. Its tendon in the 
lower half of the arm can be felt beneath the skin, on the outer side of the palmaris 
longus tendon. It is an important guide to the radial vessels which are placed in 
the hollow external to it. After passing beneath the anterior annular ligament the 
tendon is concealed by the origins of the short muscles of the thumb. Besides the 
synovial bursa enveloping the tendon beneath the annular ligament, another is 
found beneath the tendons of insertion into the metacarpus. 
The palmaris longus arises also by a single head of origin from the common 
flexor tendon from the internal condyle, from the fascia over it, and from inter- 
muscular septa on either side. It forms a short fusiform muscle, which ends in the 
middle of the forearm in a long flat tendon. This pierces the deep fascia above 
the wrist, and passing over the anterior annular ligament, is inserted (1) into the 
surface of the anterior annular ligament, and (2) into the apex of the thick central 
portion of the palmar fascia. 
The palmaris longus is the smallest muscle of the forearm. It is placed between — 
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