SERRATUS ANTERIOR 359 



Action. — The two muscles draw the scapula upward and medialward toward the spine and 

 rotate it so as to depress the shoulder. 



Relations. — Over the muscles hes the trapezius. Under them lie the serratus posterior 

 superior and the splenius cervicis, the longissimus dorsi, the iUo-costaUs, serratus posterior 

 superior and external intercostal muscles. The descending ramus of the transversa colli 

 artery descends on the deep surface. Blood-vessels for the trapezius pass to this muscle between 

 the two rhomboids. 



Variations. — There is much variation in the extent of the vertebral attachment. The 

 minor is frequently, the major occasionally, absent. The two rhomboids are frequently fused 

 with one another or may be divided into several distinct fascicuH. Frequently (80 per cent., 

 Balli) a fasciculus extends obliquely on the deep surface of the R. major from the cranial part 

 of the origin to the distal part of the insertion. Shps may be sent to the latissimus dorsi or 

 the teres major. An accessory shp may pass between the trapezius and splenius muscles to 

 the occipital bone (occipito-scapularis). A muscle corresponding to this fasciculus is normally 

 found in many mammals. 



The levator scapulae (figs. 353, 388). — Origin.~By short tendons from the dorsal tubercles 

 of the transverse processes of the first four cervical vertebrae, between the attachments of the 

 splenius cervicis and scalenus medius muscles. The tendons from the third and fourth cervical 

 vertebrae are fused for a short distance with those of the longissimus cervicis. Structure and 

 insertion. — The fibres run in parallel bundles in a dorso-lateral direction downward to the ver- 

 tebral border of the scapula opposite the supraspinous fossa. The fibre-bundles are inserted 

 directly into the periosteum. As a rule, the flat fasciculi arising from the different vertebrae 

 are easily separated. 



Nerve-supply. — By rami chiefly from the third and fourth cervical nerves. These rami enter 

 the ventral margin of the muscle and extend obhquely across the dorsal surface of the constituent 

 fascicuh about midway between the tendons of origin and insertion. Frequently anastomosing 

 branches pass between the nerves. The lowest fasciculus is usually supplied by branches from 

 the nerve to the rhomboid muscles (dorsal scapular). 



Action. — Draws the scapula upward and tends to rotate it so that the inferior angle 

 approaches the spine. When the scapula is fixed, the muscle serves to bend the neck laterally 

 and shghtly to rotate it toward the same side and extend it. 



Relations. — Externally the sterno-cleido-mastoid and, in part, the splenius capitis cover it 

 above; the trapezius, below; and the external cervical fascia, its middle portion. Internally 

 he the splenius cervicis, longissimus and iliocostalis cervicis (transversalis cervicis), and 

 serratus posterior superior muscles and the ramus descendens of the transversa colli artery. 

 In front lie the scalene muscles. 



Variations. — The number of cervical vertebrae from which the muscle springs varies from 

 two to seven. The most constant are the slips of origin from the first two vertebrae. The 

 muscle may send shps to the temporal or the occiptal bone or to the trapezius, the serratus 

 anterior (magnus), serratus posterior superior, and other muscles, or to the clavicle, first or 

 second rib, etc. Often the parts" of the muscle running to each vertebra are separated for the 

 whole distance. A bundle of fibres that appears to be a detached shp of the levator scapulae 

 may run from the first two or from lower cervical vertebrae to the lateral end of the clavicle and 

 to the acromion. This represents the levator claviculae found normally in many vertebrates. 

 According to Le Double, it is innervated by a branch from the cervical branches to the trapezius 

 group. 



The serratus anterior (mag nus) (figs. 354, 388). — First Part. — The origin is by two digita- 

 tions from the first and second ribs and from a fibrous arch uniting these two attachments. 

 The fibre-bundles converge to be inserted on an oval space on the costal surface of the scapula 

 near its medial angle. Second Part. — This arises by two or three digitations from the second, 

 third, and sometimes the fourth ribs. The fibre-bundles spread out into a thin sheet which is 

 inserted along the vertebral border of the scapula. Third Part. — This, the strongest part of the 

 muscle, arises by digitations from the fourth or fifth to the eighth or ninth ribs. The attach- 

 ments of the digitations are longest on the upper border of each rib. The interdigitate with the 

 attachments of the external oblique muscle of the abdomen. The fibre-bundles converge to be 

 inserted on the large oval space on the costal surface near the inferior angle of the scapula. 



Nerve-supply. — From the proximal portions of the anterior divisions of the fifth, sixth, 

 seventh, and sometimes the eighth cervical nerves branches arise which fuse into the long 

 .JJioracic nerve. This nerve usually passes laterally through or behind the scalenus medius 

 muscle, courses along the outer surface of the serratus anterior midway between the origin and 

 insertion, and gives rise to numerous twigs to supply the various divisions. The fibres to the 

 upper portion come mainly from the fifth cervical nerve; those to the middle from the fifth 

 and sixth; and those to the lower from the sixth and seventh. 



Action. — The muscle holds the scapula against the thorax and draws it forward and later- 

 ally and, by its highly developed inferior portion, rotates the bone so as to raise the point of 

 the shoulder. It is of especial importance in abduction of the arm. It also aids, to a slight 

 degree, in forced inspiration. 



Relations. — Superficial to the muscle lie the pectoralis major and minor, subscapularis, 

 teres major, and latissimus dorsi muscles, the subclavian and axillary vessels, and the brachial 

 plexus. Between the latissimus dorsi and pectoral muscles it is covered by skin and fascia 

 inferiorly, and superiorly by the fatty areolar tissue of the axillary fossa. Under it he the ex- 

 ternal intercostal, serratus posterior superior, and the lower extremity of the scalenus medius 

 and posterior muscles. 



Variations. — The digitations may extend to the tenth or only to the seventh rib. The 

 muscle may be continuous with the levator scapulae as it is in the carnivora, or some of its 

 upper digitations may be wanting. Slips may be continued into neighbouring muscles. The 

 lower digitations may be partially replaced by digitations innervated by intercostal nerves. 



