224 THE SHOULDER GIRDLE. [chap. 



postscapular fossa {pf), between the glenoid border and the 

 spine, also called " infraspinous fossa ; " and (3) the siib- 

 scapii/ar fossa, between the coracoid and glenoid borders, 

 on the side of the scapula opposite to the spine. 



The greater part of the scapula is ossified by edostosis (as 

 the shaft of a long bone), from a single centre, which is 

 placed not far from the middle of the bone ; but this ossifi- 

 cation does not extend into a certain portion of the superior 

 extremity. This part {siiprascapiila) either remains cartila- 

 ginous or "is feebly ossified by one or more endosteal 

 patches, or by the creeping upwards of such deposit from 

 within the main bone " (Parker). When the spine runs 

 out into a projecting acromial process, more or less of its 

 terminal portion is ossified separately as an epiphysis. 



The coracoid always ossifies from one or more separate 

 centres, and remains for some time suturally connected 

 with the scapula, though firmly ankylosing with it by the 

 time the animal has attained maturity. Sometimes (as in 

 the Sloths) it forms a considerable part of the glenoid fossa ; 

 sometimes (as in most Carnivora and Ungulata) it is a mere 

 nodule, which becomes blended with the anterior margin of 

 the fossa. 



In the Ornithodelphia (see Fig. 80), as in Birds and Rep- 

 tiles, the coracoid is largely developed, and articulates with 

 the presternum, and there is in addition a plate of bone in 

 relation with its anterior edge called epicoracoid. A small 

 plate of cartilage or bone, often found attached to the side 

 of the presternum in certain Rodents and Insectivores, is 

 considered by Parker as representing the epicoracoid of 

 the Ornithodelphia, and by Gegenbaur as the sternal ex- 

 tremity of the true coracoid, the middle part of which is 

 undeveloped. 



The clavicular arch, when completely developed, extends 



