200 



OSTEOLOGY. 



two independent precartilaginous masses, coalesce and form a bridge of bone uniting the 

 two primary ossific centres. At a later stage cartilage cells appear in the medial 



extremity of the sternal pre- 



Sternal epiphysis ossifies about Primary centres appear about nflrfilno-inmi mac a^rl ofill 



20th year ; fuses about 25th year 5th or 6th week of fetal life 



later in the lateral end of 

 the acromial mass. By the 

 growth and subsequent ossifi- 

 cation of the cartilage so 

 formed the clavicle increases 

 in length (Fawcett). 



A secondary centre ap- 

 pears at the sternal end about 



the age of twenty or later, and fusion rapidly occurring between it and the shaft, 



ossification is completed at the age of twenty-five or thereabouts. 



The Scapula. 



The scapula, or shoulder blade, is of triangular shape and flattened form. 

 It has two surfaces, costal or ventral, and dorsal. From the latter there springs 

 a triangular process called the spine, which ends laterally in the acromion; 



CLAVICULAR ARTICULAR SURFACE 



FIG. 188. OSSIFICATION OP THE CLAVICLE. 



MEDIAL ANGLE 



SUPRA-SPINOUS FOSSA 



SPINE 



VERTEBRAL MARGIN 



[NFRA-SPINOUS FOSSA 



ARTERIAL FORAMEN 



ACROMION 



ACROMIAL ANGLE 



HEAD AND GLENOID CAVITY 



NECK 

 ^GREAT SCAPULAR NOTCH 



GROOVE FOR CIRCUMFLEX SCAPULAR ARTERY 



AXILLARY MARGIN 



INFERIOR ANGLE 

 Fia. 189. THE DORSAL SURFACE OF THE RIGHT SCAPULA. 



whilst from its superior margin there arises a beak-like projection called the 

 coracoid process. The bone overlies the postero -lateral aspect of the thoracic 

 framework, reaching from the second to the seventh rib. 



