The upper edge of the latrssimus is nearly horizontal, slightly curved—its concavity up wards and free. The anterior edge is nearly vertical, and for the most part free also. The posterior or inner edge is connected throughout, and takes an extensive irregular sweep. On raising the muscle, we shall find that it was in contact with the serratus posticus inferior, the sacro-lumbalis and longissimus dorsi, the inter nal oblique and transversalis of the abdomen, the inferior rhomboid, the serratus magnus, the inferior angle of the scapula, the infra-spinatus and teres major, also with some of the ribs and intercostal muscles.
We sometimes meet a fasciculus of muscular fibres passing from the latissimus dorsi to the pectoralis major across the axillary vessels and nerves. In the Edinburgh Medical and Sur gical Journal, vol. viii. Dr. Ramsay states that it is found in one subject out of every thirty, and may prove inconvenient to the axil lary artery, vein, and nerves.
The latissimus dorsi depresses the arm, draws it backwards and inwards, rotates the humerus so as to turn the palm of the hand first in wards, then backwards. It serves to keep the lower angle of the scapula in its place. When the arm is raised and fixed, it draws the body up, as in climbing, or elevates the ribs, as in difficult respiration. In using crutches the arm is fixed by grasping the handle of the crutch, then the pectoralis major and latis simus pull up the body on the cross-bar to wards their insertions ; and when the body is so raised, it is impelled forwards by the action of this muscle, aided by the feet and by the body's own gravity.
In quadrupeds it is a muscle of progression, pulling the trunk forwards to the fore-leg, which was previously fixed. The panniculus carno sus, which is inserted close to it into the hu merus, assists in this action. In birds it is small, and consists of two portions.
Second layer.—This layer consists of the rhomboidei and levator anguli scapula?. They are seen on raising the trapezius.
The rhomboidei form a broad thin plane, separated only by a line of cellular tissue into the minor and major, extending from the spine to the scapula, and nearly concealed by the trapezius.
The rhomboideus 711i7107' arises from about half an inch of the ligamentum nucha and from the spine of the seventh cervical vertebra; its fibres run downwards and outwards to be inserted into the base of the scapula at and a little above the commencement of the spinous process of that bone. The rhomboideus major,
three or four times as broad, arises from the four or five uppermost dorsal spines, runs downwards and outwards, and is inserted below the last into the base of the scapula from its spinous process to its inferior angle. These two muscles are of the same length, thickness, and appearance in every respect, differing only in breadth. Their fibres are parallel to each beina. tendinous at their being origin, where they are blended with those of the trapezius, and are inserted between the serratus magnus and the supra- and infra spinati. The insertion of the major is peculiar; a tendinous band runs along the base of the scapula from its spine to its inferior angle, and it is into this, not into the bone, that the mus cular fibres are inserted, nearly at right angles. This band is attached only at its two extremi ties ; it is not seen till we cut a few of the posterior fleshy fibres which do reach the bone. This arrangement is supposed to allow of greater freedom of anastomosis between the scapular vessels. The minor is overlapped at its insertion by the levator anguli scapula, in the rest of its extent by the trapezius. The major is covered by the trapezius principally ; a very small part of its inferior z.ngle is covered by the latissirnus, and between these it is separated from the integuments only by the superficial fascia. The rhomboids get their name from their shape. Their opposite, but not their adjacent sides and angles are nearly equal. Their internal and external edges are attached; their superior and inferior are free. The inferior edge of the major is a little longer than any other. The deeper surface of these muscles touches the splenii, the serratus posticus superior, sacro-lumbalis and longis simus dorsi, some ribs and intercostal muscles.
These muscles draw the base of the scapula towards the spine, acting with most effect on the inferior angle, and thereby depressing the point of the shoulder. With the trapezius they draw the shoulders upwards and backwards.
In the simia the rhomboids extend to the oc ciput. In carnivora the levator major scapula seems to be their occipital portion. In the horse the levator proprius scapuice is the ante rior part of the rhomboid, arising from the ligamentum nucha.