Henry Gray (18251861). Anatomy of the Human Body. 1918.
by a slight interval, but the adjacent margins of the two muscles are occasionally united.
Variations.The vertebral and scapular attachments of the two muscles vary in extent. A small slip from the scapula to the occipital bone close to the minor occasionally occurs, the Rhomboideus occipitalis muscle.
The Levator scapulæ. (Levator anguli scapulæ) (Fig. 409) is situated at the back and side of the neck. It arises by tendinous slips from the transverse processes of the atlas and axis and from the posterior tubercles of the transverse processes of the third and fourth cervical vertebræ. It is inserted into the vertebral border of the scapula, between the medial angle and the triangular smooth surface at the root of the spine.
Variations.The number of vertebral attachments varies; a slip may extend to the occipital or mastoid, to the Trapezius, Scalene or Serratus anterior, or to the first or second rib. The muscle may be subdivided into several distinct parts from origin to insertion. Levator claviculæ from the transverse processes of one or two upper cervical vertebræ to the outer end of the clavicle corresponds to a muscle of lower animals. More or less union with the Serratus anterior.
Nerves.The Rhomboidei are supplied by the dorsal scapular nerve from the fifth cervical; the Levator scapulæ by the third and fourth cervical nerves, and frequently by a branch from the dorsal scapular.
Actions.The movements effected by the preceding muscles are numerous, as may be conceived from their extensive attachments. When the whole Trapezius is in action it retracts the scapula and braces back the shoulder; if the head be fixed, the upper part of the muscle will elevate the point of the shoulder, as in supporting weights; when the lower fibers contract they assist in depressing the scapula. The middle and lower fibers of the muscle rotate the scapula, causing elevation of the acromion. If the shoulders be fixed, the Trapezii, acting together, will draw the head directly backward; or if only one act, the head is drawn to the corresponding side.
When the Latissimus dorsi acts upon the humerus, it depresses and draws it backward, and at the same time rotates it inward. It is the muscle which is principally employed in giving a downward blow, as in felling a tree or in sabre practice. If the arm be fixed, the muscle may act in various ways upon the trunk; thus, it may raise the lower ribs and assist in forcible inspiration; or, if both arms be fixed, the two muscles may assist the abdominal muscles and Pectorales in suspending and drawing the trunk forward, as in climbing.
If the head be fixed, the Levator scapulæ raises the medial angle of the scapula; if the shoulder be fixed, the muscle inclines the neck to the corresponding side and rotates it in the same direction. The Rhomboidei carry the inferior angle backward and upward, thus producing a slight rotation of the scapula upon the side of the chest, the Rhomboideus major acting especially on the inferior angle of the scapula, through the tendinous arch by which it is inserted. The Rhomboidei, acting together with the middle and inferior fibers of the Trapezius, will retract the scapula.
The Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Walls
The muscles of the anterior and lateral thoracic regions are:
Superficial Fascia.The superficial fascia of the anterior thoracic region is continuous with that of the neck and upper extremity above, and of the abdomen below. It encloses the mamma and gives off numerous septa which pass into the gland, supporting its various lobes. From the fascia over the front of the mamma, fibrous processes pass forward to the integument and papilla; these were called by Sir A. Cooper the ligamenta suspensoria.
Pectoral Fascia.The pectoral fascia is a thin lamina, covering the surface of the Pectoralis major, and sending numerous prolongations between its fasciculi: it is attached, in the middle line, to the front of the sternum; above, to the clavicle; laterally and below it is continuous with the fascia of the shoulder, axilla, and thorax. It is very thin over the upper part of the Pectoralis major, but thicker