THE SCAPULAR MUSCLES. 571 



the scapulo-clavicularis and the sterno-clavicularis. Each of these may occur as an anomaly in 

 man, the sterno-clavicularis appearing under various forms, and passing either above, behind, 

 or in front of the clavicle. It should be stated, however, that there is a possibility that some of 

 the varieties of the sterno-clavicularis may really represent persisting portions of the muscular 

 sheet which has given rise to the middle layer of the cervical fascia and to the sterno-hyoid and 

 the omo-hyoid (page 545). 



In the lower mammals a thin muscular sheet invests a greater or less portion of the trunk 

 in intimate association with the integument, resembling in this respect the platysma. It is 

 termed the panniculiis carnosiis, and in man is normally unrepresented. Occasional traces of 

 it are found, however, and of these the most frequent is the muscle of the axillajy arch, a 

 somewhat variable band of muscle-tissue which passes across the anterior portion of the axillary 

 cavity from the lateral border of the latissimus dorsi to the tendon of the pectoralis major. It 

 presents considerable variation in its insertion, being connected sometimes with the biceps, the 

 coraco-brachialis, the pectoralis minor, or the chondro-epitrochlearis, or being united with slips 

 from the abdominal portion of the pectoralis major, or being inserted into the coracoid process 

 of the scapula. It is supplied by branches from the anterior thoracic nerves. 



{b) THE POST-AXIAL MUSCLES. 



1. Serratus magnus. 3. Rhomboideus minor. 



2. Levator anguli scapulae. 4. Rhomboideus major. 



5. Latissimus dorsi. 



I. Serratus Magnus (Fig. 558). 



Attachments. — The serratus magnus (m. serratus anterior) forms a large 

 muscular sheet covering the lateral wall of the thorax. It at'ises by nine or ten 

 fleshy digitations from the outer surfaces of the eight or nine upper ribs, the second 

 rib giving attachment to two slips. Its fibres may be regarded as arranged in three 

 groups : the uppermost group consists of fibres from the first and second ribs and ir> 

 inserted into the ventral surface of the medial angle of the scapula ; the middle group, 

 from the second and third ribs, is inserted into the ventral surface of the vertebral 

 border of the scapula ; while the remaining fibres, constituting the strongest portion 

 of the muscle, converge to the inferior angle of the same bone. 



Nerve-Supply. — By the long thoracic nerve from the fifth, sixth, and seventh 

 cervical nerves. 



Action. — It serves to keep the scapula closely applied against the thoracic 

 wall and draws it laterally. Since the portion inserted into the inferior angle is the 

 strongest, a rotation of the scapula is produced whereby its lateral angle is raised. 

 By this action the serratus plays an important part in the elevation (abduction) of 

 the arm, since, in the first place, by fixing the scapula it allows the deltoid to expend 

 all its action on the humerus instead of wasting part of it in tilting the acromion 

 downward, and, in the second place, after the deltoid has completed its action and 

 has raised the arm through about 90°, the further elevation through another right 

 angle is accomplished by a rotation of the scapula resulting from the action of the 

 serratus magnus and trapezius. 



Variations. — Absence of a portion or the whole of the muscle has been observed. Its 

 origin may extend as low as the tenth rib, and it may receive slips from the transverse processes 

 of the cervical vertebrae and from the levator scapulae. 



2. Levator Anguli Scapula (Fig. 559)- 



Attachments. — This (m. levator scapulae) is an elongated muscle on the lateral 

 surface of the neck. It arises from the transverse processes of the upper four cer- 

 vical vertebrae and passes downward, forward, and laterally to be inserted into the 

 medial angle and outer surface of the vertebral border of the scapula as far down as 

 the base of the spine. 



Nerve-Supply. — By the dorsal scapular nerve from the fifth cervical nerve. 



Action. — To draw upward the medial angle of the scapula, producing a rota- 

 tion of the bone contrary to that effected by the serratus anterior. If the scapula 

 be fixed, the action is to bend the cervical portion of the spinal column laterally, 

 rotating it slightly to the opposite side. 



