At the wrist the fascia becomes attached to the longitudinal ridges on the dorsal surface of the head of the radius, bridging thus the intervening grooves and holding the tendons in place between the ridges. The fascia then continues to form the dorsal fascia of the hand. On the ventral side of the wrist the fascia becomes thickened to form a strong =transverse ligament= (Fig. 77, 1), which is attached at its radial and ulnar ends to the carpus, and which holds in place the tendons of the 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, _n_).--This is a ribbon-like muscle lying on the lateral side of the brachium and the ventrolateral border of the antibrachium 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, _i_), 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, _h_). Inner surface with the brachialis (_i_), the extensor carpi radialis longus (_l_) and brevis, and the extensor communis digitorum (_m_).
=M. extensor carpi radialis longus= (Fig. 75, _l_; Fig. 77, _o_).--This lies along the radial side of the forearm, and connects the humerus and the second metacarpal.