Muscles of the Trunk. Those are principally the muscles which cover the breast; those which constitute the fore part and sides of the abdomen; and the great muscles that are spread over the back.

The muscles of the back are numerous and large: they arise from the whole length of the spine or back bone, having their originating fibres firmly fixed to the numerous processes or handles of that bone; from the upper and posterior edge of the pelvis; and also, some portions from the back part of the skull; and from these different organs, they spread over and cover the back of the trunk, and, run to be inserted, some into the base of the arm, others into the spine at a distance from their origin, and the remainder into the ribs and back part of the skull. They consequently not only cover and protect the whole back part of the body, but also serve to pull the head backwards, move the whole arm, assist respiration by acting on the ribs, and to raise the body by extending the spine. These are, the trapezius, or cucularis; rhomboideus; latissimus dorsi; serratus inferior et superior posticus; levator scapulae; splenius; complexus; trachelo mastoideus; rectus capitis posticus major et minor; obtiquus superior et inferior capitis sacrolumbalis; longissimus dorsi; spinalis et semi-spinalis dorsi; multifidus spine; semispmalis colli; scalenus; interspinatis et intertransversales.

The cavity of the abdomen is completed at its fore part and sides by a few broad and thin muscles, which extend from one bone to the other, having their ends firmly fixed to the edges of these bones; and passing over each other, to constitute walls for covering in and containing the bowels. These are obliquus externus and internus; transversalis; rectus abdominis and purami-dalis. These muscles also assist respiration by helping to expel the air from the lungs: and they contribute to the movement of the body, by bending it forward as in bowing, and by raising the pelvis.

The breast is covered by a few broad and strong muscles, which arise from the whole length of the breast bone, and form the fore part of the ribs, and running from each other over the chest, are inserted into the shoulder for moving the limb forward, pectoralis major; serralus magnus; levatores costarum.

The ribs are raised, and the cavity of the chest enlarged, during inspiration, by eleven double rows of small muscles on each side. They grow out from the lower edge of one rib, and are inserted into the upper rim of the next: intercostales externi et interni; sterno costales: at the fore part of the neck, close to the vertebrae, are the rectus capitis internus, major, minor et lateralis; longus coli.

Muscles isithin the Body. The principal one is called the diaphragm; it is a broad thin muscle, occupying partly a horizontal position, when the body is erect; but inclining downwards towards the back, and dividing the trunk of the body into the two great cavities, the thorax and the abdomen. It arises from the lower end of the breast bone; from the cartilages of the seventh, and of all the inferior ribs on both sides; and from the second, third, and fourth lumbar vertebrae; and from these origins its fibres run, like radii from the circumference to the centre of a circle, to be inserted into a broad flat tendon, which is situated in the middle of this muscle. The diaphragm is the principal agent in respiration, as shall be more fully described under that head.

The other muscles within the body arise from the sides of the lower end of the back bone, and from the inner surface of the pelvis, and, passing down to be inserted into the thigh bone, a little below its head, they help to turn the toes outwards, and to bend the thigh; or when the limb is fixed, they assist in bending the body, psoas parvus et magnus; illiacus internus; qua-drains lumborum.

Muscles of the Superior Extremities. These anatomists divide into the muscles that are situated on the shoulder blade, on the arm, on the fore arm, and on the hand.

The muscles situated on the shoulder blade are called muscles of the arm, because, though they arise from the former bone, which serves them as a base, yet they are inserted into the bone of the arm to effect its movements: the same observation holds with respect to the other divisions of these muscles.

The arm then is moved by seven muscles which arise from the shoulder blade, and passing over the joint are inserted into the arm bone at its upper and middle parts. The deltoides; supra et infra spinatus; teres minor et major; subscapularis et coraco brachialis; these, together with the muscles coining from the back and breast, already described, complete the motions of this part of the limb.

The fore arm is moved in flexion and extension by three muscles, which arise from the upper part of the arm bone; run down its whole length, and constitute its fulness and figure: they then pass over the elbow joint to be inserted into the upper ends of the two bones of the fore arm. These are the biceps flexor cubiti; brachialis internus et triceps extensor cubiti.

The hand is moved at the wrist by six muscles; three of these arise from the upper part of the fore arm, and descending along its whole length, are continued over the wrist, and are inserted into the hand close to this joint; they bend the hand, and are consequently called its flexors, flexor carpi ulnaris; palmaris longus et flexor carpi radialis. The three extensors, so called, because they extend the hand, and bring it backwards, arise from the lower end of the arm bone, and passing down the fore arm also, run to be inserted into the back of the hand just beyond the wrist, extensor carpi radialis, longus et brevis; extensor carpi ulnaris; all these muscles, before they reach to the wrist, become slender tendons, which is the cause of the tapering of the fore arm from about its middle to the hand.

Besides flexion and extension, the hand has a circular kind of motion called pronation and supination: the former takes place when we turn the palm down, as upon a table; the latter when we turn the palm upwards; and both motions are produced by four short muscles which extend obliquely across from one bone of the fore arm to the other, and roll the radius upon the ulna, carrying the wrist round in circles, supinator longus et brevis; pronator radii teres et quadratus.