Relations.—Outer surface with the integument, the extensor carpi ulnaris (Fig. 75, o), and the extensor digitorum lateralis (Fig. 75, n). Dorsal border with the flexor profundus digitorum (Fig. 75, q). Inner surface with the extensor brevis pollicis (Fig. 85, a).

Action as indicated by the name.

M. supinator (Fig. 85, b).—A flat muscle wrapped spirally about the proximal end of the radius.

Origin by a short, strong tendon from the lateral side of the annular ligament of the radius and by tendinous fibres from the radial collateral ligament passing from the humerus to the radius. From the tendon of origin the fibres diverge, passing toward the radial side and distad.

Insertion (Fig. 86, g).—The dorsal and part of the ventral surface of the proximal two-fifths of the radius to within five millimeters of the articular face of the head.

Relations.—Outer surface with the extensor carpi radialis brevis, extensor communis digitorum (Fig. 75, m), and extensor lateralis digitorum (Fig. 75, n). Radial border with the pronator teres (Fig. 77, q). Inner surface with the radius.

Action.—Supinator of the hand.

M. extensor brevis pollicis or extensor ossis metacarpi pollicis (Fig. 85, a) (includes M. abductor longus pollicis of man).

Origin (Fig. 86, h) by fleshy fibres from the ventral half of the lateral surface of the shaft of the ulna from the semilunar notch to the styloid process; from the ulnar half of the dorsal surface of the radius from the bicipital tubercle to a short distance distad of the middle of the bone; and from the interosseous membrane between these two areas. The fibres converge to form a strong, flat tendon (Fig. 84, d) which passes obliquely over the tendons of the extensor carpi radialis longus (e) and brevis (f) to its

Insertion into the radial side of the base of the first metacarpal. The radial sesamoid bone of the wrist is imbedded in the tendon at its insertion.

Relations.—Outer surface with the extensor carpi radialis brevis, the extensor communis digitorum (Fig. 75, m), extensor lateralis digitorum (Fig. 75, n), and extensor indicis (Fig. 85, c). Inner surface with the radius and ulna, and distad with the tendons of the two extensores carpi radiales (Fig. 84, e and f).

Action.—Extends and abducts the pollex.

B. Muscles on the Radial and Ventral Side of the Forearm (flexors and pronators).

M. pronator teres (Fig. 77, q).

Origin (Fig. 82, l) by a short strong tendon from the extremity of the medial epicondyle of the humerus.

Insertion (Fig. 86, i) by fleshy fibres and short tendinous fibres along the medial border of the radius, at its middle. The radial edge of the muscle is continuous with the strong deep layer of the antibrachial fascia.

Relations.—Outer surface with the superficial fascia. Radial border with the tendon of the biceps (Fig. 79, l′), with the extensor carpi radialis brevis (Fig. 77, p), and the supinator (Fig. 85, b). Ulnar border with the flexor carpi radialis (Fig. 77, r) and part of the flexor profundus digitorum (Fig. 77, u).

Action.—Pronates the hand by rotating the radius.

M. flexor carpi radialis (Fig. 77, r).—A slender fusiform muscle.

Origin (Fig. 82, m) from the tip of the medial epicondyle of the humerus.

Insertion.—The slender tendon passes through a deep groove between the os magnum and the first metacarpal. The groove is converted into a canal by the overlying tendons and muscles. The tendon is finally inserted into the bases of the second and third metacarpals.

Relations.—Outer surface with the pronator teres (Fig. 77, q), the superficial fascia, and the third head of the flexor profundus (u). Radial border with the pronator teres (q). Ulnar border with the third and fourth heads of the flexor profundus. Inner surface with the ulna proximad and the fifth head of the flexor profundus (u′) distad.

Action indicated by the name.

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.

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.

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.

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.

Action.—Bend the digits toward the radial side.

B. Muscles of the Thumb.

—M. abductor brevis pollicis (Fig. 77, w) (includes also the opponens pollicis of man).—A very minute, probably rudimentary muscle.

Origin from the transverse ligament (1) which connects the prominent fibrous, hairless projection that lies over the pisiform bone with the radial border of the head of the radius. The muscle passes radiodistad and ends in a very slender tendon, the insertion of which is into the base of the first phalanx of the thumb.

M. flexor brevis pollicis (Fig. 89, a).

Origin by fleshy fibres from the adjacent borders of the os magnum and scapholunar bones and from the fascia which bridges the intervening groove for the flexor carpi radialis.

Insertion by a short tendon into the base of the first phalanx of the pollex.

Action.—Flexor of the thumb.

M. adductor pollicis (Fig. 89, b).

Origin by fleshy fibres from the ventral border of the os magnum. It curves about the base of the first metacarpal on its ulnar side to its insertion.

Insertion by fleshy fibres into the base of the first phalanx of the pollex on its ulnar side.

C. Muscles Lying between the Metacarpals.

—Mm. interossei (Fig. 89).—Small stout muscles lying on the palmar surfaces of the metacarpals of the second, third, fourth, and fifth digits.

Origin by fleshy fibres from the ventral or lateral surfaces of the bases of the metacarpals. Near the distal end of the metacarpal each divides into two masses which pass onto the lateral surfaces of the metacarpal, so as to leave the ventral surface of the distal end exposed.

Insertion partly onto the lateral surfaces of the base of the first phalanx and its sesamoids, and partly by a slender tendon (Fig. 84, h) which is continued dorsad to join the extensor tendon of the digit.

D. Special Muscles of the Second Digit (the Index).

—M. flexor brevis digiti secundi (or indicis).—This name may be applied to M. interosseus of the second digit (Fig. 89, c).

M. abductor digiti secundi.—This name might be applied to a portion of the interosseus of the second digit which is sometimes differentiated from the remainder.

Origin from the radial and ventral surfaces of the base of the second metacarpal, and from the ventral surface of the trapezium.

Insertion into the radial side of the base of the first phalanx of the second digit and into its sesamoid.

M. adductor digiti secundi (Fig. 89, d).

Origin from the ventral surface of the os magnum.

Insertion into the ulnar side of the base of the first phalanx of the second digit.

E. Special Muscles of the Fifth Digit.

—M. abductor digiti quinti (Fig. 89, i).—A thick, small, conical bundle.

Origin from the distal surface of the pisiform bone and from the transverse ligament on the ulnar side of the pisiform. It ends in a slender tendon which runs along the ulnar side of the fifth metacarpal to its

Insertion into the ulnar side of the base of the first phalanx of the fifth digit.

M. flexor brevis digiti quinti (Fig. 89, h; Fig. 88, e).—This covers the ventral surface of the fifth metacarpal, and is really the interosseus of this digit.

Origin by fleshy fibres from the ventral surface of the base of the fifth metacarpal; from the ventral process of the unciform bone, and from the transverse ligament proximad of the fifth metacarpal.

Insertion by fleshy fibres into the ventral border of the proximal end of the first phalanx of the fifth digit.

M. opponens (adductor) digiti quinti (Fig. 89, g).

Origin by a flat tendon from the ventral surface of the os magnum on the ulnar side of the adductor pollicis (b). It passes toward the ulnar side and distad, the fibres diverging to their

Insertion (1) into nearly the whole of the radial surface of the fifth metacarpal, (2) into the base of its first phalanx.

V. MUSCLES OF THE PELVIC LIMBS.

1. Muscles of the Hip.

A. On the Lateral Surface of the Hip.

Fascia of the Thigh.

—After the removal of the superficial fascia with its fat and blood-vessels, there is seen a strong glistening fascia, the fascia lata (Fig. 68, z, page 117), covering the vastus lateralis muscle over the dorsal half of the thigh. Ventrally it dips between the vastus lateralis and the biceps femoris and, becoming gradually thinner, is lost on the surface of the former muscle. Passing over the dorsal border of the thigh, it extends beneath the sartorius and is attached to the dorsal border of the vastus medialis. Toward its distal end the fascia is continuous with the tendon of the biceps femoris and dorsad with the border of the sartorius muscle, while between these points it is united with the tendon of the vastus lateralis; it thus gains insertion into the patella. At its proximal end the fascia receives the insertion of the tensor fasciæ latæ (Fig. 68, r).

M. tensor fasciæ latæ (Fig. 68, r, page 117; Fig. 92, a).—The tensor fasciæ latæ is a thick triangular muscle which may be recognized by its insertion into the proximal end of the fascia lata (Fig. 68, z; Fig. 92, a′).

Origin by fleshy fibres as a thick triangular prism from the outer margin of the ventral border of the ilium craniad of the auricular impression and from the fascia covering the ventral border of the gluteus medius (Fig. 90, b) over its cranial half. The caudal border of the muscle may be continuous with the cranial border of the gluteus maximus. The muscle spreads out in a fan-like manner, covering the proximal third of the dorsal surface of the thigh. The cranial fibres pass farther distad than the others.

Insertion into the fascia lata (Fig. 68, z) along an irregular line which begins caudad at the base of the great trochanter and ends on the cranial side of the thigh at the junction of the first and second thirds.

Relations.—Outer surface with the cutaneus maximus (Fig. 62, b, page 94) and craniad with the sartorius (Fig. 68, q). Cranial border with the sartorius (q); caudodorsal border with the gluteus medius (Fig. 90, b). Inner surface with the gluteus medius, the rectus femoris (Fig. 92, b), and the vastus lateralis (Fig. 90, d).

Action indicated by the name. It also assists the quadriceps femoris in extending the leg.

M. gluteus maximus.—The gluteus maximus is a rather small quadrangular muscle in the angle between the gluteus medius (Fig. 90, b) and the caudal vertebræ.

Origin (Fig. 163, 3, page 401) by fleshy fibres from the tips of the transverse processes of the last sacral and the first caudal vertebræ, from the fascia covering the spinous muscles dorsad of the transverse processes of these vertebræ, and from the fascia covering the gluteus medius. The muscle passes laterad and slightly caudad to its

Insertion by tendon and muscle-fibres into a tubercle on the caudal side of the great trochanter at the middle of its distal end, and for a few millimeters into the ridge which continues distad from this tubercle.

Relations.—Outer surface with the caudofemoralis (Fig. 68, s, page 117), the superficial fascia, and a few fibres of the cutaneus maximus. Inner surface with the abductor caudæ internus, the tenuissimus (Fig. 90, g), the great sciatic nerve (Fig. 163, a), the obturator internus (Fig. 90, e), the gluteus medius (Fig. 90, b), the gemellus superior, and the pyriformis (Fig. 163, 7). Cranial border with the gluteus medius and the tensor fasciæ latæ. Caudal border with the caudofemoralis (Fig. 68, s).

Action.—Abducts the thigh.

M. gluteus medius (Fig. 90, b).—The gluteus medius is a very large triangular muscle which connects the ilium and the sacrum with the great trochanter (1).

Origin by fleshy fibres (1) from the superficial sacral fascia; (2) from the lateral surface of the fascia which covers the surface of the supraspinous extensor muscles of the tail; (3) from the fascia intervening between it and the tensor fasciæ latæ; (4) by tendon fibres from the dorsal half of the crest of the ilium and its dorsal border, and the dorsal half of the lateral surface craniad of the auricular impression; and (5) from the tips of the transverse processes of the last sacral and the first caudal vertebræ. The fibres converge to a strong internal tendon.

Insertion into the proximal end of the great trochanter.

Relations.—Outer surface with the gluteus maximus and tensor fasciæ latæ, and between these with the strong fascia lying beneath the cutaneus maximus muscle. Inner surface with the gluteus minimus, the pyriformis, and the gemellus superior. Cranial border with the tensor fasciæ latæ. Caudal border with the gluteus maximus.

Action.—Abducts the thigh.

M. pyriformis (Fig. 163, 7).—The pyriformis is a triangular muscle covered by the gluteus maximus and the gluteus medius (Fig. 90, b) and overlying the gemellus superior (Fig. 163, 6).

Origin by fleshy fibres from the tips of the transverse processes of the last two sacral and the first caudal vertebræ. The muscle passes laterad through the great sciatic notch to its

Insertion by a flat tendon into an elongated area on the proximal border of the great trochanter just outside (caudad) of the insertion of the gemellus superior.

Relations.—Outer surface with the gluteus medius (Fig. 90, b) and the gluteus maximus. Inner surface with the gemellus superior (Fig. 163, 6), the great sciatic nerve (Fig. 163, a), and the flexor caudæ longus (Fig. 68, x).

Action.—Abductor of the thigh.

M. gemellus superior (Fig. 163, 6).—The gemellus superior is a triangular muscle lying beneath the pyriformis (Fig. 163, 7). It is broader than the pyriformis, so that it projects beyond its borders both caudad and craniad. It is closely united craniad with the gluteus minimus, so that the limits of the two are definable only with difficulty. Its caudal border is closely united to the gemellus inferior.

Origin by fleshy fibres from an elongated area on the dorsal border of the ilium and ischium. The area is narrowed craniad. It does not quite reach the posterior inferior iliac spine in the one direction nor the spine of the ischium in the other direction. The fibres converge to a strong tendon the

Insertion of which is into a triangular area dorsad of the tip of the great trochanter.

Relations.—Outer surface with the gluteus medius (Fig. 90, b), the pyriformis (Fig. 163, 7), the great sciatic nerve (Fig. 163, a), and the gluteus maximus. Inner surface with the ilium, ischium, the capsularis, the caudal edge of the gluteus minimus (Fig. 163, 5), and the cranial edge of the obturator internus (Fig. 90, e).

Action.—Rotates the femur and abducts it so as to carry the foot outward.

M. gluteus minimus (Fig. 163, 5).—The gluteus minimus is a long triangular muscle beneath the middle of the gluteus medius (Fig. 90, b) and with its caudal border against or covering the cranial border of the gemellus superior (Fig. 163, 6), to which it is frequently closely united.

Origin from the ventral half of the ilium, from near its cranial end to a point midway between the posterior iliac spine and the spine of the ischium. The muscle ends in a strong flat tendon.

Insertion into an oval facet at the base of the dorsal surface of the great trochanter on its lateral side.

Relations.—Outer surface with the gluteus medius (Fig. 90, b) and at the caudal border with the gemellus superior (Fig. 163, 6). Inner surface with the capsularis and rectus femoris (Fig. 92, b).

Action.—Rotates the femur so as to carry the foot out.

M. capsularis (gluteus quartus, or epimeralis).—The capsularis is a small flat bundle of muscle-fibres which lies obliquely beneath the gluteus minimus (Fig. 163, 5) and gemellus superior (6) on the lateral or outer surface of the ilium.

Origin by fleshy fibres from the surface of the ilium over a triangular area between the origin of the rectus femoris (Fig. 92, b) ventrad, the gemellus superior (Fig. 163, 6) dorsad, and of the gluteus minimus (Fig. 163, 5) craniad and the acetabulum caudad. The muscle passes over the smooth surface of the ilium and the pubis ventrad of the acetabulum and then over the capsule of the joint.

Insertion by fleshy fibres for about one centimeter in the middle line on the dorsal surface of the femur distad of the great trochanter.

Relations.—Outer surface with the gluteus minimus (Fig. 163, 5), the gemellus superior (6), and the vastus lateralis (Fig. 90, d). Inner surface with the ilium, the rectus femoris (Fig. 92, b), the capsule of the joint, and the vastus medialis (Fig. 92, c).

Action.—Rotates the thigh so as to carry the foot inward, hence antagonizes the iliopsoas.

M. gemellus inferior.—The gemellus inferior is a flat triangular muscle situated just caudad of the gemellus superior and beneath the obturator internus (Fig. 90, e), so that it is seen on reflecting the latter

Origin from the dorsal one-half of the whole lateral surface of the ischium between the ischial spine and the ischial tuberosity. The fibres converge toward its insertion. The inner surface of the muscle is covered by a strong tendon.

Insertion into the inner surface of the tendon of the obturator internus (Fig. 90, e) by tendon- and muscle-fibres. Some of the muscle-fibres are inserted into the capsule of the joint.

Relations.—Outer surface with the obturator internus (Fig. 90, e). Medial surface with the ischium. Caudal border with the quadratus femoris (Fig. 90, f). Cranial border with the gemellus superior.

Action.—Abductor of the thigh. The muscle may be considered as a separate head of the obturator internus (Fig. 90, e).

M. quadratus femoris (Fig. 90, f).—The quadratus femoris is a short thick muscle connecting the ischial tuberosity (2) and the proximal end of the femur. It lies just caudad of the obturator internus (e) beneath the proximal end of the biceps femoris (Fig. 68, t).

The origin is by fleshy fibres from a considerable triangular area on the lateral surface of the ischium near the tuberosity. The area lies between the origin areas of the gemellus inferior, biceps, semimembranosus, and the obturator externus.

Insertion into the distal two-thirds of the ventral border of the great trochanter and about half the adjacent surface of the lesser trochanter.

Relations.—Outer surface with the tenuissimus (Fig. 90, g), the biceps (Fig. 68, t), the semitendinosus (Fig. 90, j), and the great sciatic nerve (Fig. 163, a). Caudal border with the semimembranosus (Fig. 90, i). Ventral border with the adductor femoris (Fig. 90, h); dorsal border with the obturator internus (Fig. 90, e) and gemellus inferior.

Action.—Extensor of the thigh and rotator of the femur so as to carry the foot inward.

M. obturator externus.—The obturator externus is a flat triangular muscle beneath the adductor femoris (Fig. 92, g).

Origin by fleshy fibres from the median lip of the obturator foramen and from both dorsal and ventral surfaces of the rami of the pubis and ischium adjacent to the lip. Also from the outer surface of the ramus of the ischium as far as the area for the quadratus femoris (Fig. 90, f). The fibres converge to a strong flat tendon.