THE SCAPULA 



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front to the pectoralis minor, and behind to the trapezoid ligament; the inferior surface is smooth 

 and directed toward the glenoid cavity, which it overhangs; the free extremity or apex gives 

 origin to the conjoined coraco-brachialis and short head of the biceps. 



The greater part of the body of the scapula and the central parts of the spinous process 

 are thin and transparent. The coracoid and acromion processes, the crest of the spine and in- 

 ferior angle, the head, neck, and axillary border, are thick and opaque. The young bone consists 

 of two layers of compact tissue with an intervening cancellous layer, but in the transparent 

 parts of the adult bone the middle layer has disappeared. The vascular foramina on the costal 

 surface transmit twigs from the subscapular and transverse scapular (suprascapular) arteries; 

 those in the infraspinous fossa, twigs from the circumflex (dorsal) and transverse scapular 

 (suprascapular) arteries, the latter also giving off vessels which enter the foramina in the supra- 

 spinous fossa. The acromion is supplied by branches from the thoraco-acromial (acromio- 

 thoracic) arterj'. 



The line of attachment of the spinous process to the dorsum of the scapula is known as the 

 morphological axis, and the obtuse angle in the subscapular fossa opposite the spine as the 



Fig. 173. — Ossification of the Scapula. 



The right Scapula at the twelfth year, showing the 

 subcoracoid element (a little larger than half 

 the natural size, i. e. |). 



Acromial cartilage 



Subcoracoid element 



Glenoid cavity 



The Scapula at the third year, 

 showing the caracoid element. (Anterior view.) 



Tee Scapula at birth. (Anterior view.) 



A 



B 



subscapular angle. From the axis three plates of bone radiate as from a centre, the prescapula 

 forward, the mesoscapula laterally, and the postscapula backward, being named in accordance 

 with the long axis of the body in the horizontal position. In the human subject the postscapula 

 is greatly developed, and this is associated with the freedom and versatility of movement 

 possessed by the upper limb. 



Ossification. — The scapula is ossified from nine centres. Of these, two (for the body of the 

 scapula and the coracoid) may be considered as primary, and the remainder as secondary. 

 The centre for the body appears in a plate of cartilage near the neck of the scapula about the 

 eighth week of intra-uterine life, and quickly forms a triangular plate of bone, from which the 

 spine appears as a slight ridge about the middle of the third month. At birth the glenoid fossa 

 and part of the scapular neck, the acromion and coracoid processes, the vertebral border and 

 inferior angle, are cartilaginous. During the first year a nucleus appears for the coracoid, and 

 at the tenth year a second centre appears for the base of the coracoid and the upper part of the 

 glenoid cavity (subcoracoid, fig. 173). 



During the fifteenth year the coracoid unites with the scapula, and about this time the other 

 secondary centres appear. Two nuclei are deposited in the acromial cartilage, and fuse to form 

 the acromion, which joins the spine at the twentieth year. The union of spine and acromion 

 may be fibrous, hence the latter is sometimes found separate in macerated specimens. The 

 cartilage along the vertebral border ossifies from two centres, one in the middle, and another at 

 the inferior angle. A thin lamina is added along the upper surface of the coracoid process and 

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