The trapezius covers the complexus, the splenii, the levator anguli scapula, the serratus posticus superior, the rhomboidei, the supra spinatus, a small portion of the infra-spinatus, the latissimus dorsi, the sacro-lumbalis and longissimus dorsi. It touches all these mus cles, and glides on them by means of a fine cellular tissue, which contains little or no fat except over die supra-spinatus. The anterior superior edge forms the posterior boundary of the great lateral triangle of the neck, and at its upper extremity is often connected with the sterno-mastoid. The two trapezii have some resemblance to the monk's cowl hanging over the neck, hence the name cucullares often given to them.
By its superior fibres this muscle raises the clavicle and scapula; by its middle it draws the scapula towards the vertebral column, and by its inferior it pulls the tubercle of the spine of the scapula downwards. If all the fibres act together, it will cause, the scapula to rotate on the thorax, so as to elevate the shoulder-joint, and in this it is powerfully assisted by the in ferior portion of the serratus magnus, as in carrying heavy burthens on the shoulder. It serves to keep the head from falling forwards, and will, by its superior fibres, draw the head to the shoulder and turn the face to the other side. We use it in shrugging up the shoulders. It becomes a muscle of inspiration by raising and fixing the clavicle and scapula, so that the subclavius, the lesser pectoral, part of the ser ratus magnus, &c. may elevate the ribs. The spinal accessory nerve (the superior external respiratory of the trunk) terminates in this muscle, and, according to Sir Charles Bell, associates it with the other respiratory muscles.
The ligamentum nuchee, from which the chief part of the cervical portion of the muscle arises, is a line of dense cellular tissue. extending from the external tuberosity of the os occipitis to the spine of the seventh cervical vertebra. It is interposed between the two trapezii. A thin septum extends from it to the spines of all the cervical vertebra. In no part does it deserve the name of ligament in the human subject. In quadrupeds, however, especially where the neck is long or the head very heavy, as in the horse, stag, elephant, &c. it is a powerful elastic ligament, resembling in structure the ligamenta subflava of the spine, and is of great impor tance by supporting the head without much muscular effort. In man it is quite rudimental.
The trapezius presents much variety in differ ent animals. In the carnivora and rodentia the clavicular portion joins with the masto-humeral, (a muscle not found in man,) and is separated. from the scapular portion by the levator anguli scapula. In the horse the only part of the muscle developed is that which corresponds to the as cending fibres in man, and which are inserted into the tubercle at the extremity of the spinous pro cesses. In the dolphin it is thin, covers all the
scapula, and is inserted into that bone near its neck. In the mole a fleshy bundle coming from the loins replaces it. In birds it consists of two portions, one for the furca, the other for the scapula. In reptiles there is no trapezius.
Latissimus dorsi.—This muscle is also thin, triangular, and very extensive, covering the lumbar region, a part of the dorsal and of the side of the thorax, and contributing to form the posterior boundary of the axilla. It is exposed by raising the integuments, superficial fascia, and lower angle of the trapezius. Then we find it arising from the tops of the spinous pro cesses of six, (sometimes of four or five, some times of seven or eight,) of the inferior dorsal vertebra, of all the lumbar vertebra and from the supraspinal ligament, from the spines and other eminences of the sacrum, from nearly the whole posterior half of the crest of the ilium, and from the three or four lowest false ribs. The fibres all converge, the uppermost running transversely, the lowest vertically. It is in serted into the posterior edge of the bicipital groove of the humerus.
The costal origin of this muscle is fleshy, all the rest is tendinous. The tendinous fibres on the vertebra are blended with those of the opposite muscle, and on the sacrum and ilium with the glutaus maximus. They form a tendon of great extent, narrow on the sacrum, very broad on the lumbar region, and again becoming narrow as we ascend to the dorsal. It is to this tendinous expansion that the name of lumbar fascia is given; its fibres are for the most part in the direction of the fleshy fibres which succeed, but they are crossed irregularly by some others. This fascia covers and binds down the lumbar muscles, giving great strength to the loins ; it is intimately connected with the tendon of the serratus posticus inferior, the internal oblique of the abdomen, and the posterior tendon of the transversalis, all of which are inseparably connected with its anterior surface. The costal origin is by fleshy slips which indigitate with similar slips of the obliquus externus abdominis ; these are so disposed that the inferior almost conceals the one above it, and on. The muscle on its way to the humerus glides over the inferior angle of the scapula, from which it receives a small fasciculus of fleshy fibres; then it bends under the teres major, forms a tendon about an inch broad and an inch long, which is connected at first by cellular tissue, and after wards by a bursa mucosa to the front of the teres major ; and is inserted into the inner or posterior edge of the bicipital groove. Some fibres of this tendon line the groove, a few pass up along its edge to the lesser tuberosity. The axillary vessels and nerves, the biceps and the coraco-brachialis, are in contact with its tendon.