HUMERUS. 105 



the glenoid cavity. It is about two inches in length and very strong ; it 

 gives attachment to several ligaments and muscles. 



Development. By six centres ; one for the body, one for the coracoid 

 process, two for the acromion, one for the inferior angle, and one for the 

 posterior border. The ossific centre for the body appears in the infra- 

 spinous fossa at about the same time with the ossification of the vertebra? ; 

 for the coracoid process during the first year ; the acromion process at 

 puberty; the inferior angle in the fifteenth year; and the posterior 

 border at seventeen or eighteen. Union between the coracoid process 

 and body takes place during the fifteenth year ; the bone is not complete 

 till manhood. 



Articulations. With the clavicle and humerus. 



Attachment of Muscles. To sixteen ; by its anterior surface to the sub- 

 scapularis ; posterior surface, supra-spinatus and infra-spinatus ; superior 

 border, omo-hyoid ; posterior border, levator anguli scapulae, rhomboideus 

 minor, rhomboideus major, and serratus magnus ; anterior border, long 

 head of the triceps, teres minor, and teres major ; upper angle of the 

 glenoid cavity, to the long tendon of the biceps ; spine and acromion to 

 the trapezius and deltoid ; coracoid process, to the pectoralis minor, short 

 head of the biceps, and coraco-brachialis. The ligaments attached to the 

 coracoid process are, the coracoid, coraco-clavicular, and coraco-humeral, 

 and the costo-coracoid membrane. 



HUMERUS. The humerus is a long bone divisible into a shaft and two 

 extremities. 



The superior extremity presents a rounded head; a constriction imme- 

 diately around the base of the head, the neck; a greater and a lesser 

 tuberosity. The greater tuberosity is situated most externally, and is 

 separated from the lesser by a vertical furrow, the bicipital groove, which 

 lodges the long tendon of the biceps. The edges of this groove below 

 the head of the bone are raised and rough, and are called the anterior and 

 posterior bicipital ridge ; the former serves for the insertion of the pecto- 

 ralis major muscle, and the latter of the latissimus dorsi and teres major. 



The constriction of the bone below the tuberosities is the surgical neck, 

 and is so named, in contradistinction to the true neck, from being the 

 seat of the accident called by surgical writers fracture of the neck of the 

 humerus. 



The shaft of the bone is prismoid at its upper part, and flattened from 

 before backwards below. Upon its outer side, at about its middle, is ;i 

 rough triangular eminence, which gives insertion to the deltoid ; and im 

 mediately on each side of this eminence is a smooth depression, corres- 

 ponding with the two heads of the brachialis anticus. Upon the innei 

 side of the middle of the shaft is a ridge, for the attachment of the coraco 

 brachialis muscle ; and behind, an oblique and shallow groove, which 

 lodges the musculo-spiral nerve and superior profunda artery. The 

 foramen for the medullary vessels is situated upon the inner surface of the 

 shaft of the bone a little below the coraco-brachial ridge ; it is directed 

 downwards. 



The lower extremity is flattened from before backwards, and is termi 

 nated inferiorly by a long articular surface, divided into tw r o parts by an 

 elevated ridge. The external portion of the articular surface is a rounded 

 protuberance, eminentia capitata, which articulates with the cup-shaped 



