dinous into anterior surface of coronoid process of ulna; action, flexes forearm; nerves, musculo-cutaneous and musculo-spiral.

Triceps extensor cubiti10: origin, scapular or long head, from rough triangular depression below glenoid fossa, the external head from posterior surface of shaft between upper part of musculospiral groove and insertion of teres major, the internal head from posterior surface below musculo-spiral groove; insertion, tendinous, back, upper surface of olecranon process of ulna; action, extends forearm and arm; nerve, musculo spiral.

Subanconeus: origin, humerus above olecranon fossa; insertion, posterior ligament of elbow; action, prevents loose capsule from being pinched during extension; nerve, musculo-spiral.

Muscles of the Forearm.

Anterior, or flexor and pronator group: All take origin from internal condyle, except pronator quadratus.

Superficial layer.

Pronator radii teres1 (Fig. 61): origin, double, above, from internal condyle and common tendon, fascia of forearm and intermuscular septum, below, from inner side of coronoid process of ulna; insertion, tendinous, into rough ridge on middle of outer surface of shaft of radius; action, pronates forearm, aids flexion; nerve, median.

Flexor carpii radialis 5: origin, internal condyle by common tendon, forearm fascia, and intermuscular septa; insertion, tendinous, into base of index metacarpal; action, flexes wrist, then forearm; nerve, median.

Palmaris longus: origin, inner condyle by common tendon, fascia, and intermuscular septa; insertion, tendinous, into anterior annular ligament and palmar fascia; action, tightens palmar fascia; nerve, median.

Flexor carpi ulnaris: origin, double, by common tendon from inner condyle and from inner margin of olecranon by aponeurosis, and from upper two-thirds of posterior border of ulna and intermuscular septum; insertion, tendinous, into pisiform bone, annular ligament and base of little finger metacarpal; action, flexes hand on forearm; then forearm on arm; nerve, ulnar.

Flexor sublimis digitorum (perforatus): origin, by three heads, one from internal condyle by common tendon and from internal lateral ligament and intermuscular septa, a second from inner side of the coronoid process of ulna, the third from oblique line of radius; insertion, by four tendons, each of which splits for the passage of the deep flexor tendons, each half becoming attached to middle of lateral margins of second phalanges; action, flexes fingers, then hand on forearm, then forearm on arm; nerve, median.

Deep layer,

Flexor profundus digitorum (perforans): origin, upper two-thirds of antero-internal surface of shaft of ulna, inner side of coronoid process, by an aponeurosis from upper twothirds of posterior border of ulna and ulnar half of interosseous membrane; insertion, into bases of last phalanges by four tendons, which pass between the two slips of flexor sublimis tendons; action, flexes fingers, then wrist on forearm; nerves, ulnar and anterior interosseous.

Flexor longus pollicis: origin, upper twothirds of front of shaft of radius, adjacent interosseous membrane, sometimes from base of coronoid process; insertion, base of last phalanx of thumb; action, flexes last thumb phalanx; nerve, anterior interosseous.

Pronator quadratus: origin, oblique line on lower fourth of anterior surface of ulna, the bone below, the anterior border of ulna and

FIG. 61.

aponeurosis over muscles; insertion, lower fourth of anterior surface and external border of radius; action, pronates hand; nerve, anterior interosseous.

Radial Region: all the extensors and supinators arise, at least partially, from the external condyle and ridge of the humerus. Supinator longus13: origin, upper two-thirds of external condyloid

ridge and external intermuscular septum; insertion, base of styloid process of radius; action, supinates forearm after it has been pronated, flexes forearm on arm, second in power only to biceps; nerve, musculo-spiral.

Extensor carpi radialis longior 5 (Fig. 62): origin, lower third of external condyloid ridge and external intermuscular septum; insertion, radial side of base of metacarpal bone of index finger; action, extends wrist; nerve, musculo-spiral.

FIG. 62.

Extensor carpi radialis brevior: origin, external condyle by common tendon, external lateral ligament, the covering aponeurosis and the intermuscular septa; insertion, radial side of base of metacarpal of middle finger; action, extends wrist; nerve, posterior inter

Osseous.

Extensor communis digitorum: origin, external condyle by common tendon, deep fascia and intermuscular septa; insertion, second and third phalanges of each finger by three main tendons, one of which subdivides into two; action, extends fingers, then hand, finally forearm on arm; nerve, posterior interosseous.

Extensor minimi digiti9: origin, common tendon and intermuscular septa; insertion, with tendon of common extensor in to second and third phalanges of little finger; action, extends little finger; nerve, posterior inter

Osseous.

Extensor carpi ulnaris10: origin, by common tendon from external condyle, middle third of posterior border of ulna below aconeus and forearm fascia; insertion, ulnar side of base of fifth metacarpal; action, extends

wrist; nerve, posterior interosseous.

Anconeus: origin, back of outer condyle of humerus; insertion, side of olecranon and upper fourth of posterior surface of shaft of ulna; action, extends forearm; nerve, musculo-spiral.

Supinator brevis11: origin, external condyle of humerus, external lateral ligament and orbicular ligament of radius, oblique line of ulna, triangular depression in front of it and aponeurosis covering muscle; insertion, back inner part of neck of radius, bicipital tuberosity, and oblique line; action, supinates forearm; nerve, posterior interosseous which pierces it.

Extensor ossis metacarpi pollicis 13: origin, posterior surface of shaft of ulna below anconeus, interosseous ligament, and middle third of posterior surface of shaft of radius; insertion, base of thumb-metacarpal; action, extends thumb-metacarpal; nerve, posterior interosseous.

Extensor primi internodii pollicis: origin, posterior surface of shaft of radius and interosseous membrane; insertion, base of first thumb-phalanx; action, extends phalanx on metacarpal; nerve, posterior interosseous.

Extensor secundi internodii pollicis: origin, posterior surface of shaft of ulna and interosseous membrane below extensor ossis metacarpi; insertion, last phalanx of thumb; action, extends thumb; nerve, posterior interosseous.

Extensor indicis: origin, posterior surface of shaft of ulna below extensor secundi; insertion, with tendon of common extensor into second and third phalanges of index finger; action, extends index finger; nerve, posterior interosseous.

Fascia of the Hand.

The anterior annular ligament is stretched between pisiform bone and unciform process of unciform bone on one side, and the tuberosity of scaphoid and ridge of trapezium on the other; it is continuous with forearm and palmar fascia, and receives the insertion of the palmaris longus muscle and partially that of flexor carpi radialis, which pierces it; beneath it pass the median nerve and, in one synovial sheath, the tendons of the flexor sublimis and profundus digitorum and the flexor longus pollicis.

The post rior annular ligament, continuous with forearm fascia, is attached on dorsum internally to ulna, cuneiform, and pisiform bones and palmar fascia, externally to ridges on back of and margin of radius. Six separate synovial compartments exist for the ex

tensor tendons; from without inward, they are: (1) outer side of styloid process, for extensor ossis metacarpi and extensor primi internodii pollicis; (2) behind same process, for extensor carpi radialis longior and brevior; (3) next for extensor secundi internodii pollicis; (4) more internally still, for extensor communis digitorum and extensor indicis; (5) opposite interval between radius and ulna, for extensor minimi digiti; and (6) back of ulna, for extensor carpi ulnaris.

The palmar fascia (Fig. 61), consisting of a central and two lateral portions, invests muscles of hand forming their common sheath; the central segment is triangular, attached to anterior annular ligament above, below dividing into four slips opposite metacarpal heads, each slip dividing again to enclose flexor tendons and be inserted on sides of first phalanges; strong transverse fibres connect the separate processes, and vertical septa, continuous on each side with interosseous aponeurosis, separate the middle from lateral palmar groups of muscles; beneath is the superficial palmar arch, median and ulnar nerves; the lateral portions of this fascia thinly invest the muscles of the thenar and hypothenar eminences.

Muscles of the Hand.

Abductor pollicis" (Fig. 61): origin, ridge of trapezium and annular ligament; insertion, tendinous into radial side of base of first thumb-phalanx; action, draws thumb from median line—i. e., abducts it; nerve, median.

Opponens pollicis: origin, palmar surface of trapezium and annular ligament; insertion, whole length of radial side of thumbmetacarpal; action, flexes metacarpal; nerve, median.

Flexor brevis pollicis12 (Fig. 61): origin, by two heads between which lies flexor longus pollicis tendon, the external from trapezium and outer two-thirds of annular ligament, the internal from trapezoid, os magnum, base of third metacarpal, and sheath of tendon of flexor carpi radialis; insertion, sides of base of first thumb-phalanx by two tendons each containing a sesamoid bone; action, as name implies; nerves, median and ulnar.

Adductor pollicis: origin, whole palmar length of metacarpal of middle finger; insertion, ulnar side of base of first thumb-phalanx