xiv] GENERAL CHARACTERS. 225 



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 Mr. 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. 73, mss). At the sternal extremity there may be two 

 distinct pieces, the one (pe) nearest the clavicle being the 

 supposed homologue of a displaced fragment of the pre- 

 coracoid of the lower vertebrates. The one (pst) nearest the 

 sternum is called omostemum by Parker, and episternum by 

 Gegenbaur, who considers it homologous with the so-called 

 episternum (interdavide, Parker) of the Ornithodelphia and 

 Lizards. *' 



Spedal CJiaraders of the 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 back- 

 wards 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 "ex- 

 ternal " or " axillary," looks downwards and rather forwards ; 

 and the coracoid border is " superior." The postscapular 

 fossa is much developed, and the suprascapular border is 

 long, straight, and forms an acute angle with the glenoid 

 border. At the junction of the coracoid border of the 



£ula with the coracoid bone, there is a more or less well- 

 ted notch (coraco-scapular notch). The spine is well 

 • 



