THE SCAPULA, OR SHOULDER BLADE 



177 



ossification takes place in the middle of thecoraeoid process, which usually becomes joined with 

 the rest of the bone at the time when the other centres make their appearance. Between the 

 fourteenth and twentieth years ossification of the remaining centres takes place in quick 

 .succession, and in the following order : first, in th^ root of the coracoid process, in the form of 

 a broad scale; second, near the base of the acromion process; third, in the inferior angle and 

 contiguous part of the posterior border; fourth, near the extremity of the acromion; fifth, 

 in the posterior border. The acromion process, besides being formed of two separate nuclei, 

 has its base formed by an extension into it of the centre of ossification which belongs to the 

 spine, the extent of which varies in different cases. The two separate nuclei unite and then 

 join with the extension from the spine. These various epiphyses become joined to the bone 

 between the ages of twenty-two and 

 twenty-five years. Sometimes fail- 

 ure of union between the acromion 

 process and spine occurs, the junc- 

 tion being effected by fibrous tissue 

 or by an imperfect articulation; in 

 some cases of supposed fracture 

 of the acromion with ligamentous 

 union it is probable that the de- 

 tached segment was never united to 

 the rest of the bone. The upper 

 third of the glenoid cavity is usually 

 ossified from a separate centre (sub- 

 coracoid) which makes its appearance 

 between the tenth and eleventh 

 years. Very often, in addition, an 

 epiphysis appears for the lower part 

 of the glenoid cavity. 



Articulations. With the hu- 

 merus and clavicle. 



Attachment of Muscles. To 

 ftrvrtitt'cn to the anterior surface, 

 theSubscapularis; posterior surface, 

 Supraspinatus, Infraspinatus; spine, 

 Trapezius, Deltoid; superior border, 

 Omohyoid; vertebral border, Serra- 

 tus magnus, Levator anguli scapulae, 

 Rhoraboideus, minor and major; 

 axillary border, Triceps, Teres 

 minor, Teres major; apex of glen- 

 oid cavity, long head of the Biceps; 

 coracoid process, short head of the 

 Biceps, Coracobrachialis, Pectoralis 

 minor; and to the inferior angle oc- 

 casionally a few fibres of the Latissi- 

 mus dorsi. 



Surface Form. The only parts 

 of the scapula which are truly sub- 

 cutaneous are the spine and acro- 

 mion process, but, in addition to these, the coracoid process, the internal or vertebral border 

 and inferior angle, and, to a less extent, the axillary border, may be defined. The acro- 

 mion process and spine of the scapula are easily felt throughout their entire length, forming, 

 with the clavicle, the arch of the shoulder. The acromion can be ascertained to be connected 

 to the clavicle at the acromioclavicular joint by running the finger along it, its position being 

 often indicated by an irregularity or bony outgrowth from the clavicle close to the joint. The 

 acromion can be felt forming the point of the shoulder, and from this can be traced backward to 

 join the spine of the scapula. The place of junction is usually denoted by a prominence, which 

 is sometimes called the acromial angle. From here the spine of the scapula can be felt as a 

 prominent ridge of bone, marked on the surface as an oblique depression, which becomes less 

 and less distinct, and terminates a little external to the spinous processes of the vertebra?. Its 

 termination is usually indicated by a slight dimple in the skin on a level with the interval be- 

 tween the third and fourth thoracic spines. Below this point the vertebral border of the scapula 

 may be traced, running downward and outward, and thus diverging from the vertebral spines, 

 to the inferior angle of the bone, which can be recognized, although covered by the Latissimus 

 dorsi muscle. From this angle the axillary border can usually be traced through this thick 

 muscular covering, forming, with the muscles, the posterior fold of the axilla. The coracoid 



12 



FIG. 140. Plan of the development of the scapula. From 

 seven centres. The epiphyses (except one for the coracoid pro- 

 cess) appear from fifteen to seventeen years, and unite between 

 twenty-two and twenty-five years of age. 



