xiv.] PRIM A TES. 249 



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

 undeveloped. 



The clavicular arch, when completely developed, extends 

 from the free acromial extremity of the spine of the scapula 

 to the anterior extremity of the presternum. 



It consists mainly of an elongated rod of bone, ossified 

 usually in fibrous tissue, but at either extremity are certain 

 patches of true cartilage, which may become converted into 

 bone, or may sometimes degenerate into fibro-cartilage. 

 These are thus described and named by Parker. At the 

 scapular extremity of the clavicle, there is often a piece of 

 cartilage considered to be segmented off from the end 

 of the mesoscapula, and hence called mesoscapular segment 

 (Fig. 77, fuss). At the sternal extremity there may be two 

 distinct pieces, the one (pc] nearest the clavicle being the 

 supposed homologue of a displaced fragment of the pre- 

 coracoid (Gegenbaur and Parker) of the lower vertebrates. 

 The one (ost) nearest the sternum is called omostermtm by 

 Parker, and episternum by Gegenbaur, who considers it 

 homologous with the so-called episternum (intei'davicle, 

 Parker) of the Ornithodelphia and Lizards. 



Special Characters of tke Shoulder Girdle in the Different 



Groups of the Mammalia. 



Order PRIMATES. Man. In the ordinary erect position 

 of the human body, the -suprascapular border is directed 

 backwards and inwards, and is commonly called the " base ' 

 or " vertebral border " of the scapula ; the glenoid cavity 

 looks forwards and outwards ; the glenoid border, called 

 " external ' : or " axillary," looks downwards and rather 

 forwards ; and the coracoid border is " superior." The 



