Trapezius.
Latissimus Dorsi.

Direction. The body should be placed in the prone position, with the arms extended over the sides of the table, and the chest and abdomen supported by several blocks, so as to render the muscles tense. An incision should then be made along the middle line of the back, from the occipital protuberance to the coccyx. From the upper end of this, a transverse incision should extend to the mastoid process; and from the lower end a third incision should be made along the crest of the ilium to about its middle. This large intervening space, for convenience of dissection, should be subdivided by a fourth incision, extending obliquely from the spinous process of the last dorsal vertebra, upwards and outwards, to the acromion process. This incision corresponds with the lower border of the Trapezius muscle. The flaps of integument should then be removed in the direction shewn in the accompanying figure.

The Trapezius is a broad, flat, triangular muscle, placed immediately beneath the skin, and covering the upper and back part of the neck and shoulders. It arises from the occipital protuberance and inner third of the superior curved line of the occipital bone; from the ligamentum nuchse, the spinous processes of the seventh cervical, and all the dorsal vertebras, and from the corresponding portion of the supra-spinous ligament. From these points the muscular fibres proceed, the superior ones downwards and outwards, the inferior ones upwards and outwards, and the middle fibres horizon- tally, and are inserted, the superior ones curving forwards into the outer third of the posterior border of the clavicle, the middle fibres into the upper margin of the acromion process, and into the whole length of the upper border of the spine of the scapula; the inferior fibres converge near the scapula, and are attached to a triangular aponeurosis, which glides over a small triangular surface at the inner extremity of the spine, and is inserted into a small tubercle in immediate connection with its outer part. The Trapezius is fleshy in the greater part of its extent, but tendinous at its origin and insertion. At its occipital origin, it is connected to the bone by a thin fibrous lamina, firmly adherent to the skin, and wanting the lustrous, shining appearance of aponeurosis. At its origin from the spines of the vertebrae, it is connected by means of a broad semi-elliptical aponeurosis, which occupies the space between the sixth cervical and the third dorsal vertebrae, and forms, with the muscle of the opposite side, a tendinous ellipse. The remaining part of the origin is effected by numerous short tendinous fibres. If the Trapezius is dissected on both sides, the two muscles resemble a trapezium, or diamond-shaped quadrangle; two angles, corresponding to the shoulders; a third, to the occipital protuberance; and the fourth, to the spinous process of the last dorsal vertebra.

The clavicular insertion of this muscle varies as to the extent of its attachment; it sometimes advances as far as the middle of the clavicle, and may even become blended witli the posterior edge of the Sterno-mastoid, or overlap its margin. This should be borne in mind in the operation for tying the subclavian artery.

Relations. By its superficial surface, with the integument to which it is closely adherent above, but separated below by an aponeurotic lamina. By its deep surface, in the neck, with the Complexus, Splenius, Levator anguli scapula, and Rhomboideus minor; in the back, with the Rhomboideus major, Supra-spinatus, Infra-spinatus, a small portion of the Serratus posticus superior, the intervertebral aponeurosis which separates it from the Erector spinae, and with the Latissimus dorsi. The spinal accessory nerve passes beneath the anterior border of this muscle, near the clavicle. The outer margin of its cervical portion forms the posterior boundary of the large posterior triangle of the neck, the other boundaries being the Sterno-mastoid in front, and the clavicle below.

The Ligamentum Nuchte (fig. 143) is a thin band of condensed cellulo-fibrous membrane, placed in the line of union between the two Trapezii in the neck. It extends from the external occipital protuberance to the spinous process of the seventh cervical vertebra, where it is continuous with the supra-spinous ligament. From its anterior surface a fibrous slip is given off to the spinous processes of each of the cervical vertebras, excepting the atlas, so as to form a septum between the muscles on each side of the neck. In the human subject, it is merely the rudiment of an important elastic ligament, which serves to sustain the weight of the head in some of the lower animals.

The Latissimus Dorsi is a broad flat muscle, which covers the lumbar and lower half of the dorsal regions, and is gradually contracted into a narrow fasciculus at its insertion into the humerus. It arises by tendinous fibres from the spinous processes of the six inferior dorsal, from those of the lumbar and sacral vertebrae, and from the supra-spinous ligament. Over the sacrum, the aponeurosis of this muscle blends with the tendon of the Erector spinae. It also arises from the external lip of the crest of the ilium, behind the origin of the External oblique, and by fleshy digitations from the three or four lower ribs, being interposed between similar processes of the External oblique muscle. From this extensive origin the fibres pass in different directions, the upper ones horizontally, the middle ones obliquely upwards, and the lower ones vertically upwards, so as to converge and form a thick fasciculus, which crosses the inferior angle of the scapula, and occasionally receives a few fibres from it. The muscle then curves around the lower border of the Teres major, and is twisted upon itself, so that the superior fibres become at first posterior and then inferior, and the vertical fibres at first anterior and then superior. It then terminates in a short quadrilateral tendon, about three inches in length, which, passing in front of the tendon of the Teres major, is inserted into the bottom of the bicipital groove of the humerus, above the insertion of the tendon of the Pectoralis major. The lower border of the tendon of this muscle is united with that of the Teres major, the surfaces of the two being separated by a synovial bursa; a second synovial bursa is interposed between the muscle and the inferior angle of the scapula.

The origin of this muscle from the spine and ilium is effected by an aponeu-rosis, which assists in forming the sheath for the Erector spinae. Its costal attachment takes place by means of three or four fleshy slips, which inter-digitate with the External oblique muscle of the abdomen.

Relations. Its superficial surface is subcutaneous, excepting at its upper part, where it is covered by the Trapezius. By its deep surface, it is in relation with the Erector spinae, the Serratus posticus inferior, Intercostal muscles and ribs, the Serratus magnus, inferior angle of the scapula, Rhomboideus major, Infra-spinatus, and Teres major. Its external margin is separated below, from the external oblique, by a small triangular interval; and another triangular interval exists between its superior border and the margin of the Trapezius, in which the Intercostal and Rhomboideus major muscles are exposed.

Nerves. The Trapezius is supplied by the spinal accessory and cervical plexus; the Latissimus dorsi, by the subscapular nerves.