THE SHOULDER-GIRDLE. 227 



Posteriorly is the trapezius muscle superficially, and beneath are the omohyoid, 

 levator scapidtz, and the two rhomboid muscles. 



The trapezius arises from the superior curved line of the occiput, the liga- 

 mentum nuchae, and the spines of the seven cervical and all of the thoracic vertebrae. 

 It inserts into the upper surface of the outer third of the clavicle, acromion process, 

 and spine of the scapula to near its root. Its upper fibres directly aid in sustaining 

 the weight of the upper extremity. It is not infrequently paralyzed, and then falling 

 of the shoulder is marked. It also tends to pull the scapula backward toward the 

 spine, and rotates it. 



The levator scapulae arises from the transverse processes of the upper four 

 cervical vertebrae and passes downward to insert into the posterior edge of the 

 scapula between its upper angle and the root of the spine of the scapula. 



The scapula is supported largely by this muscle; hence when the trapezius is 

 paralyzed, as occurs in division of its motor nerve, the spinal accessory, this muscle 

 is utilized in counteracting its loss. 



The rhomboid muscles arise from the lower part of the ligamentum nuchae 

 and the spines of the seventh cervical and upper five thoracic vertebrae and insert 

 into the posterior edge of the lower three-fourths of the scapula. 



The serratus anterior (magnus) muscle (Fig. 202), lies beneath the scapula 

 and arises from nine slips from the outer surface of the upper eight or nine ribs; 

 the second rib receives two slips. It passes backward and upward and inserts into 

 the posterior edge of the scapula from its upper to its lower angle. 



The serration attached to the sixth rib is the one that reaches farthest forward 

 on the side of the chest. 



The omohyoid muscle arises posteriorly from the upper border of the 

 scapula, just behind the suprascapular notch, and then runs upward and forward to 

 the under surface of the body of the hyoid bone. It is a digastric or two-bellied 

 muscle and its middle tendbn is attached by a pulley-like process of the deep cervical 

 fascia to the first rib. 



MOVEMENTS OF THE SHOULDER-GIRDLE. 



While the muscles above enumerated comprise all those directly attached to the 

 shoulder-girdle and trunk, they are of course assisted to some extent by the muscles 

 forming the axillary folds, viz., the pectoralis major anteriorly and the latissimus 

 dorsi and teres major posteriorly. 



The shoulder-girdle is elevated by the upper fibres of the trapezius, levator 

 scapulae, rhomboidei, sternomastoid (clavicular origin), and omohyoid. It is depressed 

 by the lower fibres of the trapezius, latissimus dorsi, lower fibres of the serratus ante- 

 rior (magnus), pectoralis major, pectoralis minor, and subclavius. It is drawn forward 

 by the pectoralis major, minor, subclavius, serratus anterior, omohyoid, and, if the 

 arm is fixed, by the teres major muscles. It is drawn back by the trapezius, rhomboidei, 

 and latissimus dorsi muscles. Rotation is effected by a combined action of various 

 parts of these muscles. 



SURFACE ANATOMY. 



On observing the region of the shoulder it is noticed that it projects well out 

 from the trunk, so that the arm hangs free. It has as its framework three bones 

 the clavicle and scapula above, forming the shoulder-girdle, and the humerus below. 

 They radiate from the region of the joint, the clavicle toward the front, the scapula 

 toward the back, and the humerus downward, forming the basis of the shape of the 

 shoulder, which is modified by the muscles, fat, and skin. 



The skin and fat bridge over and tend to obliterate the hollows and to a less 

 extent obscure the prominences. This is more the case as applied to the muscles 

 than the bones, hence the bones form the better landmarks or guides. 



Age and sex modify the surface appearances. In children the bones are but 

 slightly developed and their prominences not marked. Fat is usually abundant and it 

 is often no easy task to recognize by the sense of touch the various anatomical parts 

 and determine whether or not they have been injured. For this reason one should 



