SERRATUS MAGNUS. ACTIONS. 207 



trapezoid parts of the coraco-clavicular ligament. It is covered in front by 

 the costo-coracoid membrane or fascia. 



' The serratus magnus muscle, placed upon the upper and lateral part of 

 the thorax, between the ribs and the scapula, is attached anteriorly by nine 

 fleshy angular slips to the first eight or sometimes nine ribs, two of these 

 being connected with the second rib ; it also derives some fibres from the 

 aponeurosis covering the upper intercostal spaces. Posteriorly, the muscle, 

 considerably narrowed, is attached to the line in fro at of the base of the 

 scapula, and at the upper and lower angles of the bone into the flat surfaces 

 which are excluded from the fossa of the subscapular muscle. The fibres 

 are arranged in three sets, thus a. Those from the first and second digita- 

 tions form a thick bundle which terminates on the flat area in front of the 

 upper angle of the scapula ; 6. those of the third and fourth digitations, but 

 especially the first of these, which is the inferior digitation of the second rib, 

 spread out into a triangular layer, the thinnest part of the muscle, and are 

 attached along the line in front of the base of the scapula, extending from 

 the place of insertion of the preceding part nearly to the lower angle of the 

 bone ; c. the remaining five or six digitations converge in the form of a fan, 

 and terminate in a thick mass, which is attached posteriorly to the flat sur- 

 face in front of the lower angle of the scapula. 



By its deep surface, the serratus magnus rests on the upper ribs, the intercostal 

 muscles, and part of the serratus posticus superior. Its outer surface'is in contact 

 posteriorly with the subscapular muscle, and forms anteriorly the internal wall of the 

 axilla, being subcutaneous in the lower part of its extent. 



Not unfrequently the number of digitations, and the number of the ribs with 

 which the muscle is connected, are greater than above described. Occasionally the 

 attachment to the first rib is wanting ; and examples are recorded of the absence of 

 the middle part of the muscle. 



ACTIONS. Considered with reference to the movements of the limb upon the trunk, 

 the upper part of the trapezius, the levator scapulae, and the rhomboid muscles are 

 elevators of the shoulder ; the lower part of the trapezius, the pectoralis minor and 

 the subclavius are depressors ; the serratus magnus as a whole carries forward the 

 base of the scapula, and the rhomboidei draw it back ; the latissimus dorsi and 

 pectoralis major depress the humerus and carry it towards the middle line, behind or 

 in front, according as the one or other muscle is in action. 



More particularly, the superior fibres of the trapezius elevates the clavicle ; the 

 succeeding fibres acting on the acromion have also some elevating action, but tend 

 rather to carry back the scapula towards the spine ; the inferior part of the muscle 

 acting upon the spine of the scapula would of itself depress that bone while it carried 

 it inwards towards the dorsal spines, but acting in concert with the upper two-thirds 

 of the muscle, a rotation is produced in the scapula round a central point in such a 

 manner that while the whole bone, and more especially the acromion, is raised and 

 carried towards the dorsal spines, the upper angle of the scapula is somewhat 

 depressed and carried inwards, while the lower angle is carried outwards and elevated. 



The levator anguli scapulce, in elevating the superior angle of the scapula, counter- 

 acts in some degree the rotating action of the trapezius ; and this is further effected by 

 the rhomboid muscles, more especially the greater, which, as its main attachment is 

 near the inferior angle of the scapula, necessarily tends to raise that part and bring it 

 nearer to the dorsal spines. In this manner, when the trapezius, levator, and rhomboid 

 muscles act together, the scapula is raised without rotation, and its base is carried at 

 the same time inwards towards the dorsal spines. 



The sukclavuis, by depressing the clavicle, diminishes the space between that bone 

 and the first rib, and may probably act principally as a support to the sterno-clavicular 

 articulation. 



The pectoralis minor, in bringing the coracoid process downwards and forwards, 

 tends to throw the lower angle of the scapula backwards. 



