222 APPLIED ANATOMY. 



The greater tuberosity projects considerably beyond the acromion process and 

 therefore forms the most prominent part of the shoulder. Immediately below the 

 tuberosities is the surgical neck. It is described as being the portion between the 

 tuberosities above and the insertions of the pectoralis major and latissimus dorsi 

 muscles below. It is a common site for fractures. Half way down the shaft on its 

 outer side is the rough deltoid eminence for the insertion of the deltoid muscle. 



Sternoclavicular Joint. The ligaments uniting the inner end of the clavicle 

 to the thorax at the upper end of the sternum are the interclamcular, which passes 

 from one clavicle to the other across the top of the sternum, the anterior and. posterior 

 Sternoclavicular, and the rhomboid or costoclavicular ligament which passes from the 

 clavicle downward and forward to the first rib. This last one limits displacement in 

 cases of luxation. There is a fibrocartilaginous disk between the clavicle and sternum, 

 forming two distinct joint cavities. The line of the joint slopes downward and outward. 



Acromioclavicular Joint. The outer end of the clavicle articulates with the 

 acromion process by a joint whose surface inclines down and inward, thus favoring 

 displacements of the clavicle upward. The ligaments joining them are called the 

 superior and inferior acromioclavicular. In reality they are simply the thickened 

 portions of the capsular ligament. This capsular ligament is ruptured in the not infre- 

 quent cases of luxation which occur here. Running from the under surface of the 

 clavicle, a short distance from its outer end, to the coracoid process below, is the 



Anterior Sternoclavicular Costoclavicular or rhomboid ligament 

 Interclavicular ligament _ / / Clavicle 



Interarticular fibrocartilage s 



Tendon of 

 subclavius muscle 



First rib 



| 



^ First piece of sternum 



FIG. 235. Sternoclavicular joint and attachments of the inner end of the clavicle. 



coracoclavicular ligament. It is composed of two parts, an antero-external square 

 ligament called the trapezoid, and a postero-internal conical one called the conoid. 



The bone may be fractured just external to these ligaments, giving rise to a peculiar 

 deformity to which attention will be called in describing the fractures of the clavicle. 



From the coracoid process the coraco-acromial ligament runs outward and up- 

 ward to the acromion process, the coracohumeral outward and downward to the neck 

 of the humerus, and the costocoracoid ligament inward to the first rib at its cartilage. 



The Shoulder-joint. The upper extremity being an organ of prehension and 

 not of support, the shoulder-joint, which is the articulation which connects it with the 

 trunk through the shoulder-girdle, is constructed with the idea in view of favoring 

 and permitting motion, and not of supporting weight or resisting force. Hence we 

 find it to be a ball-and-socket joint, the one which allows of the freest movements. 



The glenoid cavity is a shallow excavation, not a deep cup, as in the hip. The 

 articulating surface of the head of the humerus is extensive but not so large as it 

 would have been had the scapula not been made to move on the thorax. The 

 clavicle keeps the joint well out from the side of the body; hence the neck of the 

 humerus is short. The movements of the arm are so extensive and free that we do 

 not have the tuberosities of the humerus so large and set so far away from the artic- 

 ular surface as is the case with the femur and its trochanters. 



If the upper portion of the femur was like the upper end of the humerus, the 

 lower extremity would be continually rolling in or out, making walking or running 

 at least difficult if not impossible. Thus we see that the shape of the bones is 

 dependent on the character of their functions. 



