THE SHOULDER-GIRDLE. 



219 



The landmarks of the shoulder are formed by the bones and muscles; hence a 

 brief review of their important characters will serve as a basis for the surface anatomy 

 which follows. 



THE BONES OF THE SHOULDER. 



The bones entering into the construction of, and forming the basis on which the 

 shoulder is constructed are the clavicle and scapula, forming the shoulder-girdle, and 

 the humerus. 



The clavicle is a comparatively long and slender bone that acts as a prop to 

 keep the point of the shoulder out from the trunk. The inner extremity is large and 

 rests with its flat surface on the upper outer edge of the sternum, with the inter- 

 position of a disk of fibrocartilage. Its outer extremity is flattened ; it articulates by 



Trapezius 



Deltoid 



Pectoralis major 



FIG. 230. Right clavicle, upper surface. 



means of a gliding joint with the acromion process of the scapula, and it is connected 

 with the base of the coracoid process beneath by ligaments. It is double curved, the 

 large curve having its convexity forward and embracing the inner two-thirds of the 

 bone, and the small curve having its concavity forward, forming the outer third. 



At the deepest part of the concavity of the anterior edge, about at the junction 

 of its outer and middle thirds, is a small rough eminence called the deltoid tiibercle 

 because of the attachment to it of the deltoid muscle. At a corresponding point on 

 the posterior and under surface of the bone is a prominent projection called the conoid 

 tubercle ; to this is attached the conoid ligament. Running forward and outward 

 from this tubercle on the under surface is a rough line which serves as the point of 



Pectoralis major 



rhomboid liga 

 FIG. 231. Right clavicle, under surface. 



Sternohyoid 



attachment of the trapezoid ligament. Both these ligaments are of importance in 

 relation to the fractures of this bone. 



The middle third of the bone is its weakest part. Attached to the clavicle on 

 its anterior surface are the deltoid muscle on its outer third and the pectoralis major 

 on its inner half. On its posterior and upper surfaces are the trapezius at its -outer 

 third, and the clavicular head of the sternomastoid on its inner third. The subclavius 

 muscle is attached to its under surface. It will thus be seen that there is a space equal 

 to one-sixth of the length of the bone inferiorly and one-third of the bone superiorly 

 which is free from muscular attachments, and it is here that it is most frequently 

 fractured. 



The Scapula. The scapula is spoken of as having a body, neck, spine, and 

 acromion, glenoid, and coracoid processes; an upper, an anterior, and a posterior border; 

 and an upper and a lower angle. It is not often spoken of as possessing a head, the 

 glenoid process or that portion being sometimes so called in which the glenoid cavity 

 or fossa for the articulation of the humerus is situated. 



