THE SHOULDER-GIRDLE. 



Anatomical neck 



Greater tuberosity. 



Lesser tuberosity and 



facet for subscapu- 



laris muscle 



Bicipital groove 



Surgical neck 



FIG. 233. Anterior surface of upper end of humerus. 



The head is comparatively small and cup-shaped, with the glenoid fossa on its 

 surface for the head of the humerus. It is joined to the body of the bone by a narrow 

 constriction called the neck. Fractures through this neck are rare. Above and pos- 

 terior to the glenoid fossa is the acromion process and spine of the scapula, and above 

 and anterior is the coracoid process. 



The spine of the scapula runs upward and forward across the upper and posterior 

 surface of the bone. Its commencement 

 at the posterior edge of the bone is called 

 its root; this is over the fourth rib and 

 opposite the third thoracic spine. The 

 posterior edge of the scapula opposite 

 the root of the spine projects backward, 

 but this is not the superior angle, which is 

 still higher up. The spine of the scapula 

 ends anteriorly in the acromion process. 

 This projects far beyond the glenoid cav- 

 ity, overhangs the head of the humerus, 

 and forms the point of the shoulder. It, 

 as well as the rest of the spine, is subcu- 

 taneous and is a valuable landmark. 



The acromion process is not so often 

 fractured as one would expect. It articu- 

 lates with the clavicle and the bones are 

 not infrequently luxated at this point. 



The coracoid process projects 

 forward underneath the clavicle to the 

 upper and inner side of the head of the 

 humerus. It is about 2.5 cm. (i in.) 

 below the clavicle and just to the outer 

 side of the junction of its middle and outer thirds. It lies just underneath the inner edge 

 of the deltoid muscle, hence it is not always easily felt. It is almost never fractured, 

 but is especially valuable as a landmark in injuries and operations on the shoulder. 



The two great hollows above and below the spine are the supra- and infraspinous 

 fosscz for the supra- and infraspinatus muscles. The angles are at the two extremities 



of the posterior border. The 

 superior angle receives the in- 

 sertion of the levator scapulae 

 muscle and is covered by the 

 trapeziiis which inserts into the 

 spine and thus obscures its out- 

 line. The inferior angle is cross- 

 ed by the upper edge of the 

 latissimus dorsi -muscle, from 

 which it sometimes receives a 

 few fibres. This angle is ren- 

 dered prominent when the fore- 

 arm is flexed on the arm and 

 placed across the back. 



The Humerus. The 

 upper end of the humerus is 

 composed of a head joined to 

 the tuberosities through the 

 medium of the anatomical neck. 

 The head projects inwardly from 

 the shaft at an angle of 1 20 degrees to it. The lesser tuberosity has inserted into it 

 the subscapularis muscle; it presents forward. To its outer side and separating it 

 from the greater tuberosity is the bicipital groove for the long tendon of the biceps 

 muscle. To the outer side of the groove is the greater tuberosity with its three facets 

 for the supraspinatus , infraspinatus, and tcres minor muscles. 



Anatomical neck 

 Facet for infra- 

 spinatus muscle 

 Facet for teres 

 minor muscle 



Surgical neck 



Facet for supra- 

 spinatus muscle 

 Bicipital groove 



Greater tuberosity 

 Lesser tuberosity 



FIG. 234.- Outer surface of upper end of humerus. 



