538 MAMMALIAN ANATOMY 



magnus, the levator anguli scapulae, and the subscapularis. To the 

 head, the biceps and the coraco-brachialis. 



Blood Supply. The scapula is supplied with blood mainly by 

 the suprascapular and subscapular arteries. The general distribution 

 of the suprascapular artery is to the supraspinous fossa and the distal 

 anterior end of the subscapular fossa, while the subscapular artery 

 enters the bone in the infraspinous fossa, the axillary border, and the 

 proximal end of the subscapular fossa. 



Ossification. The scapula appears to develop from at least four 

 principal centres (Fig. 423). The first to appear is the centre for the 

 body and the spine ; then small centres appear in the acromion and 

 metacromion. At about forty days the coracoid process begins to 

 ossify ; at seventy days a centre begins in the upper part of the 

 glenoid cavity. The margin of the vertebral border and the tips of 

 the coracoid process and acromion remain for a long time cartilaginous. 



VARIATIONS IN THE SCAPULA. 

 VAKIATIONS IN SIZE. 



The measurements of the scapula are taken as follows : 



The breadth is the diameter on a line from the vertebral border at 

 the origin of the spine to the middle of the inner edge of the head. 



It would be more natural to call this diameter the length, because 

 on the scapula of the cat it is the greater, but, inasmuch as it is termed 

 the breadth in human anatomy, for purposes of comparison it will be 

 more convenient so to designate it in the table. 



The length is the diameter from the superior angle to the inferior 

 angle. 



The width of the supraspinous fossa is the distance taken on the 

 length of the scapula from the superior angle to the edge of the 

 spine. 



The width of the infraspinous fossa is the distance taken as above 

 from the inferior angle to the edge of the spine. 



These two diameters are not absolutely correct, owing to the fact 

 that the edge of the spine overhangs the infraspinous fossa. 



The long diameter of the glenoid cavity is the antero-posterior 

 diameter from the tip of the supraglenoid tubercle to the posterior 

 margin. 



The short diameter is the greatest transverse diameter. 



