Part 44

Relations.--Outer surface with the integument and the palmaris longus (Fig. 77, s). Inner surface and ulnar border with the flexor profundus digitorum.

Action indicated by the name.

=M. flexor sublimis digitorum= (or perforatus).--This muscle is in two parts, which are given a common name only because of the similar structure and insertions of their tendons.

The =ulnar part= (Fig. 77, x) is a conical muscle taking origin from the outer surface of the tendon and muscle of the palmaris longus and from the adjacent ligament. It gives rise to two or three tendons (Fig. 88, b) which arise from distinct slips of the muscle; these pass to the ulnar two or three digits. That passing to the fourth or fifth digit receives an accessory slip from a small mass of fibres attached to the transverse ligament on the radial side of the palmaris tendon.

The =radial part= is a small flat triangular muscle which takes origin from the outer surface of the tendon formed by the junction of the tendons of the first and second parts of the flexor profundus. It divides into two slips, each giving rise to a tendon. These tendons (Fig. 88, b′) pass to the second and third digits. That to the third digit may divide into two, one of which goes to the fourth digit.

Each of the four tendons (Fig. 88, b and b′) is perforated by a tendon of the flexor profundus (Fig. 88, c) as it passes through the fibrous pulley-ring at the base of the first phalanx. It then continues beneath the flexor profundus tendon through the second pulley-ring (2) and is inserted into the base of the second phalanx.

Relations.--Outer surface of the ulnar part with the integument; inner surface with the palmaris longus (Fig. 77, s). Outer surface of the radial part with the palmaris longus; inner surface with the flexor profundus.

Action.--Flexor of the second phalanx of digits 2-5.

=M. flexor profundus digitorum= (or perforans).--This arises by five heads, the tendons of which join one another at the wrist to make the strongest and deepest of the flexor tendons.

The first or ulnar head has origin (Fig. 87, g) from the dorsal half of the medial (radial) surface of the ulna from the proximal lip of the semilunar notch to within a centimeter of the styloid process. Its fibres converge to a large flat tendon which forms the lateral (ulnar) and superficial part of the common tendon.

a, M. pronator quadratus; b, tendon of M. biceps; c, conjoined tendon of M. brachialis and M. clavobrachialis; d, insertion of caput longum of M. triceps; e, insertion of short portion of caput mediale of M. triceps; f, origin of M. flexor carpi ulnaris; g, origin of first head of M. flexor profundus digitorum; h, origin of fifth head of M. flexor profundus digitorum; i, intermediate portion of caput mediale of M. triceps.]

The second head has origin (Fig. 82, n) from the distal end of the medial epicondyle of the humerus between the flexor ulnaris and the third and fourth heads of the profundus. It may be very closely attached to these muscles at their origins. Its tendon joins the radial border of the tendon of the first head. From this junction the radial part of the flexor sublimis arises.

The third head (Fig. 77, u) has origin (Fig. 82, o) by a strong tendon from the medial epicondyle of the humerus, between the palmaris (p) and flexor radialis (m). Its tendon forms the radial part of the common tendon.

The fourth head has origin by a strong tendon from the medial epicondyle of the humerus just ventrad of the origin of the second head and the flexor ulnaris, to which many of its fibres are attached. Its tendon forms the middle and superficial part of the common tendon.

The fifth or radial head (Fig. 75, q; Fig. 77, u′) has origin (Fig. 87, h) from the middle third of the ventral surface of the shaft of the radius over an area limited by two oblique bony ridges; from the adjacent parts of the interosseous membrane; and from the ventral part of the medial surface of the shaft of the ulna between a point about two centimeters distad of the semilunar notch and the junction of the middle and distal thirds of the shaft. Its very thick tendon forms the middle and deep part of the common tendon.

The common tendon (Fig. 88, c′) covers the carpus and metacarpus ventrally. It divides into five tendons (c) which pass to the five digits and are inserted into the bases of the terminal phalanges. Those of the first four digits perforate the tendon of the flexor sublimis (b) at the base of the first phalanx of each digit. At the same place each passes through a fibrous pulley-ring attached to the base of the phalanx. Each then passes through a second pulley-ring (2) near the head of the phalanx and is finally inserted into the base of the terminal phalanx.

Relations.--Outer surface with the pronator teres (Fig. 77, q), flexor carpi radialis (Fig. 77, r), palmaris longus (s), flexor carpi ulnaris (t), integument, and extensor carpi ulnaris (Fig. 75, o). Inner surface with the radius, ulna, interosseous membrane and pronator quadratus (Fig. 87, a).

Action.--Flexor of all the digits.

The integument, fibrous pads, and the palmaris longus (except the ends of its tendons) have been removed; the flexor sublimis has been cut. a, cut ends of tendons of M. palmaris longus; b, tendons of M. flexor sublimis digitorum, ulnar division; b′, radial part of M. flexor sublimis digitorum; c, tendons of M. flexor profundus digitorum (c′, the common tendon); d, M. abductor digiti quinti; e, M. flexor brevis digiti quinti; f, Mm. lumbricales (f′, their tendons). 1, transverse ligament of wrist; 2, annular ligaments.]

=M. pronator quadratus= (Fig. 87, a).--A thick quadrangular muscle whose fibres run obliquely between the distal ends of the ulna and radius.

Origin by fleshy fibres from about the distal half of the ventral (flexor) surface or border of the ulna and from the interosseous membrane adjacent to the area. The fibres pass obliquely distad toward the radial side to their

Insertion by fleshy fibres into the ventral (flexor) surface of the radius distad of the area of origin of the fifth head of the profundus.

Relations.--Outer surface with the flexor profundus. Inner surface with the radius, ulna, and interosseous membrane.

Action as indicated by the name.

4. =Muscles of the Hand.=

A. BETWEEN THE TENDONS.--=Mm. lumbricales= (Fig. 88, f, f′).--Four small muscles in the palm of the hand.

Origin by fleshy fibres from the outer (palmar) surface of the tendon common to the ulnar four parts of the profundus (c′).

Insertion (f′).--The four slips are flat at their origin. Each becomes cylindrical and curves about the base of one of the four ulnar digits and is inserted into the radial side of the base of the first phalanx close to its ventral border.