MUSCLES OF THE THORACIC LIMBS. 173 



flexor muscles. Distad of the transverse ligament the fascia 

 spreads out in the palm of the hand, and becomes united with 

 the fibrous pad which is situated here. On the fingers the 

 fascia becomes attached to the phalanges, forming tendinous 

 sheaths, the so-called vaginal ligaments, for the flexor 

 muscles. Near the base and the head of the first phalanx 

 strong, narrow, ring-like bands, the annular ligaments (Fig. 

 88, 2), are formed in these sheaths; these surround and bind 

 down the tendons of the flexor muscles. 



A. MUSCLES ON THE ULNAR AND DORSAL SIDE OF THE 

 FOREARM (extensors and supinators) (Fig. 75, p. 158). 



M. brachioradialis or supinator longus (Fig. 75, k; Fig. 

 77, ;/). This is a ribbon-like muscle lying on the lateral side 

 of the brachium and the ventrolateral border of the antibra- 

 chium just beneath the superficial fascia. It connects the 

 humerus and the radius. 



Origin. By a thin tendon from about the middle fifth of 

 the dorsal border of the humerus, or sometimes proximad of 

 the middle. The muscle curves over the outer surface of the 

 brachialis (Fig. 75, z), to which it is closely applied, and runs 

 along the lateral border of the antibrachium to its insertion. 



Insertion by a short tendon into the ridge which forms the 

 ventral limit of the groove on the outer surface of the styloid 

 process of the radius and upon the adjacent ligaments. 



Relations. Outer surface with the integument, and at the 

 proximal end with the caput laterale of the triceps (Fig. 75, //). 

 Inner surface with the brachialis (z), the extensor carpi radialis 

 longus (/) and brevis, and the extensor communis digitorum (;;/). 



Action. Supinator of the hand. 



M. extensor carpi radialis longus (Fig. 75, /; Fig. 77, 

 o). This lies along the radial side of the forearm, and con- 

 nects the humerus and the second metacarpal. 



Origin (Fig. 8 1 , k] from the middle portion of the lateral 

 supracondyloid ridge between the origin of the brachialis (_/) 

 and the anconeus. About the middle of the forearm the 

 muscle ends in a slender tendon (Fig. 84, e] which passes 

 through the groove on the radial side of the dorsal surface of 

 the distal end of the radius. 



