MUSCLES OF THE UPPER EXTREMITY 



435 



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 Rhom- 

 boideus occipitalis muscle. 



The Levator scapulae- (Levator anguli scapula?} (Fig. 409) is situated at the 

 back and side of the neck. It arises by tendinous slips from the transverse pro- 

 cesses of the atlas and axis and from the posterior tubercles of the transverse 

 processes of the third and fourth cervical vertebrae. It is inserted into the verte- 

 bral 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 claviculce from the 

 transverse processes of one or two upper cervical vertebrae to the outer end of the clavicle corre- 

 sponds 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 scapulae 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 con- 

 ceived 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 jn 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 inspira- 

 tion; 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 scapulae 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 direc- 

 tion. 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 Rhom- 

 boidei, 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: 



Pectoral is major. 

 Pectoralis minor. 



Subclavius. 

 Serratus anterior. 



Superficial Fascia.- The superficial fascia of the anterior thoracic region is con- 

 tinuous 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 



