The deltoid (see Pl.
and 5) is the muscle which forms the shoulder cap and is used in abducting the arm to a right angle with the trunk; it runs from the clavicle, acromial process and spine of the scapula, to the middle of the hUmerus, and is supplied by the circumflex nerve. Several short rotating muscles pass from the scapula to the upper end of the humerus; these are the subscapularis passing in front of the shoulder joint, the supraspinatus above the joint, and the infraspinatus and teres minor behind. The teres major (P1.
and 5) comes from near the lower angle of the scapula, and is in serted with the latissimus dorsi into the front of the surgical neck of the humerus. The coracobrachialis (P1. II.–I) passes from the coracoid process to the middle of the humerus in front of the shoulder joint, while the brachialis anticus passes in front of the elbow from the humerus to the coronoid process of the ulna. Pass ing in front of both shoulder and elbow is the biceps (Pl. II.–I), the long head of which rises from the top of the glenoid cavity in side the joint, while the short head comes from the coracoid pro cess. The insertion is into the tubercle of the radius. These three muscles are all supplied by the same (musculo-cutaneous) nerve. At the back of the arm is the triceps (Pl. 11.-2) which passes behind both shoulder and elbow joints and is the great extensor muscle of them; its long head rises from just below the glenoid cavity of the scapula, while the inner and outer heads come from the back of the humerus. It is inserted into the olecranon process of the ulna and is supplied by the musculo-spinal nerve. The mus cles of the front of the forearm form superficial and deep sets (Pl.
Most of the superficial muscles come from the internal condyle of the humerus. From without inward they are the pro nator radii teres going to the radius, the flexor carpi radialis to the base of the index metacarpal bone, the palmaris longus to the palmar fascia, the flexor sublimis digitorum to the middle pha langes of the fingers, and the flexor carpi ulnaris to the pisiform bone. The important points of practical interest about these mus cles are noticed in the article ANATOMY (Superficial and Artistic). In addition to these the brachio-radialis is a flexor of the forearm, though it arises from the outer supracondylar ridge of the hu merus. It is supplied by the musculo-spiral nerve, the flexor carpi ulnaris by the ulnar, the rest by the median. The deep muscles of the front of the forearm consist of the flexor longus pollicis run ning from the radius to the terminal phalanx of the thumb, the flexor profundus digitorum from the ulna to the terminal phalanges of the fingers, and the pronator quadratus passing across from the lower third of the ulna to the same amount of the radius. These three muscles are supplied by the anterior interosseous branch of the median nerve, but the flexor profundus digitorum has an extra twig from the ulnar. The extensor muscles at the back of the fore arm are also divided into superficial and deep sets (see P1. 11.-2). The former rise from the region of the external condyle of the humerus, and consist of the extensor carpi radialis longior and brevior inserted into the index and medius metacarpal bones, the extensor communis digitorum to the middle and distal phalanges of the fingers, the extensor minimi digiti, the extensor carpi ulnaris passing to the metatarsal bone of the minimus, and the supinator brevis wrapping round the neck of the radius to which it is in serted. The aconeus which runs from the external condyle to the olecranon process is really a part of the triceps. The deep mus Iles rise from the posterior surfaces of the radius and ulna, and are the extensor ossis metacarpi pollicis, the name of which gives its insertion, the extensor brevis pollicis to the proximal phalanx, and the extensor longus pollicis to the distal phalanx of the thumb, while the extensor indicis joins the extensor communis slip to the index finger ; all these posterior muscles are supplied by the poste rior interosseous nerve. In front and behind the wrist the tendons are bound down by the anterior and posterior annular ligaments, while on the flexor surface of each linger is a strong fibrous sheath or theca for the flexor tendons.
The ball of the thumb is occupied by short muscles called the the nar group, while hypothenar mus cles are found in the ball of the little finger. The four lumbrical muscles (fig. 2) run from the flexor profundus digitorum ten dons to those of the extensor communis between the heads of the metacarpal bones while, ris ing from the shafts of these bones, are the three palmar and four dorsal interosseous muscles (fig. 2) which also are inserted into the extensor tendons. The two outer lumbricals and the thenar muscles are supplied by the median nerve ; all the other hand muscles by the ulnar.
On the front of the thigh the quadriceps extensor muscles are the most important : there are four of these, the rectus femoris (fig. 1) with its straight and reflected heads rising from just above the acetabulum, the crureus, deep to this, from the front of the femur, and the vastus externus and internus wrapping round the femur on each side from the linea aspera. All these are inserted into the patella, or rather the patella is a sesamoid bone developed where their common tendon passes round the lower end of the femur when the knee is bent. The distal part of this tendon, which passes from the patella to the tubercle of the tibia, is the ligamentum patellae. The sartorius is a long riband-like muscle running from the an terior superior spine of the ilium to the inner surface of the tibia, obliquely across the front of the thigh. It forms the outer bound ary of Scarpa's triangle, the inner limit of which is the adductor longus and the base Poupart's ligament. The floor is formed by the iliacus from the iliac fossa of the pelvis, which joins the psoas, to be inserted with it into the lesser trochanter, and by the pec tineus running from the upper ramus of the pubis to just below the insertion of the last muscles. The adductor muscles, longus, brevis and magnus, all rise from the subpubic arch, and are in serted into the linea aspera of the femur, so that they draw the femur toward the middle line. The gracilis (Pl. 11.-3) is part of the adductor mass, though its insertion is into the upper part of the tibia. The extensor muscles of the front of the thigh are supplied by the anterior crural nerve, but the adductor group on the inner side from the obturator. The pectineus is often supplied from both sources. On the back of the thigh the gluteus maximus (Pl. 1.-5 and Pl. plays a great part in determining man's outline (see
ANATOMY: Superficial and Artistic). It rises from the sacral re gion, and is inserted into the upper part of the femur and the deep fascia of the thigh, which is very thick and is known as the fascia lata; the muscle is a great extensor of the hip and raises the body from the stooping position. The gluteus medius rises from the ilium, above the hip joint, and passes to the great trochanter; it abducts the hip and enables the body to be balanced on one leg, as in taking a step forward. The gluteus minimus is covered by the last muscle, and passes from the ilium to the front of the great trochanter, thus rotating the hip joint inward. Some of its anterior fibres are sometimes separate from the rest, and are then called the scansorius. When the gluteus maximus is removed, a number of short externally rotating muscles are seen, rising from the pelvis and inserted into the great trochanter (P1. II.-4) ; these are, from above downward, the piriformts, gemellus superior, obturator in ternus, gemellus inferior and quadratus femoris. They are all supplied by special branches of the sacral plexus. On cutting the quadratus femoris a good deal of the obturator externus can be seen, coming from the outer surface of the obturator membrane and passing to the digital fossa of the great trochanter. Unlike the rest of this group, it is supplied by the obturator nerve. Com ing from the anterior part of the crest of the ilium is the tensor fasciae femoris, which is inserted into the fascia lata, as is part of the gluteus maximus, and the thickened band of fascia which runs down the outer side of the thigh from these to the head of the tibia is known as the ilio tibial band. The tensor fasciae fe moris, gluteus medius and minimus, are supplied by the superior gluteal nerve, the gluteus maximus by the inferior gluteal. At the back of the thigh are the hamstrings rising from the tuberosity of the ischium (P1. 11.-4) ; these are the semimembranosus and semi tendinosus, passing to the inner part of the upper end of the tibia and forming the internal hamstrings, and the biceps femoris or ex ternal hamstring, which has an extra head from the shaft of the femur and is inserted into the head of the fibula. These muscles are supplied by the great sciatic nerve and extend the hip joint while they flex the knee. In the leg, as distinguished from the thigh, are three groups of muscles, anterior, external and posterior. The anterior group (Pl. 11.-3) all come from the front of the tibia and fibula, and consist of the extensor longus digitorum, extend ing the middle and distal phalanges of the four outer toes, the extensor proprius hallucis, extending the big toe, and the peroneus tertius, a purely human muscle inserted into the base of the fifth metatarsal bone. All these are supplied by the anterior tibial nerve.