M. palmaris longus ([Fig. 77], s).—A flat fusiform muscle beneath the fascia on the medial border of the forearm.
Origin ([Fig. 82], p) by a short flat tendon from the distal part of the medial surface of the medial epicondyle of the humerus.
About one centimeter from the wrist the muscle ends in a flat tendon which passes through the transverse ligament and divides on the hand into four or five (or sometimes only three) tendons ([Fig. 77], s′) which diverge to the insertions. The ulnar portion of the flexor sublimis digitorum ([Fig. 77], x) takes origin from the common tendon before its division.
Insertion.—Each tendon except the first gives off a branch which spreads out in the trilobed pad in the palm. The middle two of these may be traced to the integument covering the pad. The tendon is then inserted ([Fig. 88], a) near the base of the first phalanx onto the outer surface of the perforated portion of the flexor sublimis tendon (b, b′) at its side, except that to the thumb, which divides near its distal end into two which are inserted into the sesamoid bones at the base of the first phalanx. The tendons of insertion are closely united to the fibrous pulley-ring at the base of the first phalanx, and each may send a slip to the base of the phalanx at either side of the ring.
Relations.—Outer surface with the superficial fascia and one head of the flexor sublimis ([Fig. 77], x). Radial border with the flexor carpi radialis. Ulnar border with the flexor carpi ulnaris and a part of the flexor profundus digitorum. Inner surface with the flexor carpi radialis (r), the flexor carpi ulnaris (t), the flexor profundus digitorum (u), and the radial head of the flexor sublimis digitorum.
Action.—Flexor of the first phalanx of each of the digits.
M. flexor carpi ulnaris ([Fig. 77], t, t′).
Origin.—There are two heads. The first or humeral head (t′) takes origin in common with the second part of the flexor profundus from the median surface of the distal end of the humerus just distad of the medial epicondyle ([Fig. 82], q). The second or ulnar head (t) takes origin by fleshy fibres from the lateral surface of the olecranon and from the dorsal border of the ulna from the olecranon to a point distad of the semilunar notch ([Fig. 87], f). The two heads join proximad of the middle of the forearm. The muscle passes obliquely across the ventral surface of the forearm to its
Insertion by fleshy and tendinous fibres into the proximal surface of the pisiform bone.
Relations.—Outer surface with the integument and the palmaris longus ([Fig. 77], s). Inner surface and ulnar border with the flexor profundus digitorum.