193 MUSCLES OF THE UPPER LIMB. 



sets, internal and external, proceeding respectively from the inner and outer 

 divisions of the plexus, the outer supplying the gi'eat pectoral muscle, the inner 

 hoth it and the lesser pectoral. 



Actions of the muscles passing- between the Trunk and Upper Limb. — 

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

 upper part of the trapezius, the levator scapula; and the rhomboid muscles are 

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

 and the subclavius are depressors : the sen-atus magnus as a whole canies for- 

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

 dorsi and pectoralis major depress the humeiais 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 tr/ijM'ziii.i elevate the clavicle ; the 

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

 tend rather to carry back the scapula towards the spine ; the inferior pai-t of the 

 muscle acting ujion the spine of the scapula woaild 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 roimd 

 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 uj^per angle of 

 the scapula is somewhat depressed and carried inwards, while the lower angle is 

 canied outwards and elevated. 



The Irrafor anrpili .wiipulcp and rlinmhoUh'l elevate the superior angle and base 

 of the scajsula. thus counteracting in some degree the rotating action of the 

 trapezius. 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 xuhclavlu.s depresses the clavicle, and may also act as a support to the 

 stemo-clavicular articulation. 



The jx'cf oralis minor draws the coracoid process downwards and forwards, 

 and tends to throw the lower angle of the scapula backwards. 



The ftf'vrafu.'i wtif//nix nluscle. by withdrawing the base of the scapula from the 

 spinal column, enables the arm when raised from the shoulder to be still farther out- 

 stretched, as in the movement termed extension in fencing. It comes powerfully 

 into action in all movements of pushing ; it likewise combines ■n-ith the trapezius 

 in rotating the scapula. In forced inspiration, the scapula being fixed by the 

 muscles which attach it to the tnink posteriorly and superiorly, the serratus 

 magnus assists in dilating the chest by raising and expanding the ribs. 



The liit'tMimti.i dorxl carries the elevated arm doumwards and backwards, rotat- 

 ing it at the same time inwards, so as to make the palm look backwards, thus 

 accomplishing such a movement as is made by the arm in swimming. By pass- 

 ing over the angle of the scapula it binds that process to the tinink. preventing 

 its projection backwards ; and by being folded round the outer border of the 

 scapula, it limits the projection outwards of the same angle when the ami is 

 raised. 



The 2}''Pt<>7'(7lis viajor muscle, while it combines with the latissimus dorsi in 

 depressing the humerus from the raised position, opposes that muscle by drawing 

 the limb forwards. It is placed upon the stretch when the arms are thrown 

 backwards, and is most shortened when they are folded across the chest. In the 

 remarkable case of Groux, affected with congenital cleft sternum, when the 

 shoulders were fixed backwards, the action of the great pectoral muscles tended to 

 separate the two segments of the sternum, and increased the space in which the 

 motions of the heart could be observed through the integuments. 



Considered as acting on the trunk from the upper limb in a fixed condition, 

 these muscles all tend to draw the trunk of the body towards the limb, as in 

 climbing, or other like efforts. The latissimus dorsi muscles, if acting on both 

 sides, carry the body upwards and forwards, as in the use of crutches. The 

 pectorales and latissimus dorsi are also muscles of forced inspiration, tending to 

 raise and expand the ribs, more especially when the shoulders are fixed and the 

 arms are elevated. The upper parts of both trapezii acting on the occipital bone 

 aid the stemo-mastoid muscle in throwing forward the chin ; and if one muscle 

 only acts, it aids iu rotating the head. 



