THE SCAPULA 111 



The following muscles are attached to the clavicle: — 



Sterno-cleido-mastoid. Trapezius. 



Pectoralis major. Sterno-hyoid. 



Subclavius. Stemo-thyroid (occasionally). 



Deltoid. 



Ligaments : — 



Interclavicular. Interarticular (acromio-clavicular) . 



Interarticular (sternal). Conoid. 



Capsular (sterno-clavicular). Trai)ezoid. 



Rhomboid or costo-clavicular. Costo-coracoid membrane. 



Capsular (acromio-clavicular). Deep cervical fascia. 



Blood-supply. — The nutrient artery is a Ijninch of the suprascapular; it enters 

 the bone on the under surface of the shaft near the middle of the subcla^dan groove. 

 It is directed towards the acromial end. The acromial end of the clavicle receives 

 numerous branches from the acromio-thoracic artery, and twigs from the arteries 

 in the muscles attached to it. 



Ossification. — The clavicle is ossified from two centres. The primary nucleus 

 appears in the sixth week of eml^ryonic life in the tissue immediately overlying the 

 cartilaginous pre-coracoid bar (see p. 115). The cla^dcle begins as a membrane- 

 bone, but the ossification quickly extends into the underlying cartilage; it is 

 therefore a dermal splint engrafted on cartilage. About the seventeenth year a 

 secondary nucleus appears at the sternal end. Consolidation is complete by the 

 twentieth year. 



THE SCAPULA 



The scapula is a large flat bone, triangular in shape, situated on the posterior 

 aspect of the thorax, and resting on the ribs from the second to the seventh. Of 

 its two surfaces the anterior is deeply concave, forming the subscapular fossa, 

 which is marked by several ridges commencing at the posterior border of the bone 

 and passing obliquely upwards; these ridges divide this surface into several shallow 

 grooves from which the suhHcapularls muscle takes origin: the highest groove is the 

 deepest. The outer third of this surface is smooth, and overlapped by the sub- 

 scapular muscle: the superior and inferior angles are somewhat triangular, and 

 connected by a narrow ridge of bone along the posterior border. This ridge and 

 its terminal surfaces serve for the insertion of the seiratus magnvs. 



The posterior surface, or dorsum, is generally convex; it is unequally divided 

 by a prominent ridge of bone, the spine. The hollow above the spine is the supra- 

 spinous fossa, and lodges the supra-.spinatus muscle. The part below the spine is 

 the infraspinous fossa; it is larger than the supraspinous fossa, and is limited 

 inf(n-iorly by a ridge which runs from the glenoid fossa backwards to join the 

 posterior border a short distance above the inferior angle. To this oblique ridge 

 the stout aponeurosis is attached which separates the teres major and teres minor 

 muscles from the infraspinatus muscle. The infraspinatus arises from the inner 

 two-thirds of the infraspinous fossa, and overlaps the outer third. The supra- and 

 infraspinous fossse communicate with each other around the outer end of the 

 spine; this part corresponds to the neck of the scapula, and the groove is the 

 scapular notch ; it transmits the suprascapular nerve and artery from one fossa to 

 the other. The surface of bone lielow the ol)lique ridge presents two, and occa- 

 sionally three, facets for muscles: the long narrow outer one is for the origin of the 

 teres minor ; this is cro.ssed near its middle by a groove for the dorsal artery of the 



