THE HUMAN STERNUM 41 



ossicles which have been lost in maceration ; and others (in groups 2 and 4) 

 may be associated with variations in the mode of articulation of the clavicle 

 or attachments of the sterno-clavicular ligaments. 



Significance of Suprasternal Ossifications. 



It is thus evident that these suprasternal ossifications are both rare 

 and variable in their occurrence. The nodules may be separate or fused 

 together ; separate from the presternum or attached to it ; bilateral or median 

 in position. 



They are vestigial structures, and several views have been formulated 

 regarding their homologies. They have been regarded as representative of 

 costal, shoulder-girdle, or sternal elements. Breschet,* who first described 

 them, inclined to the belief that they represent the persistent distal ends of 

 cervical ribs, the more proximal portions of which had not been developed. 

 This notion does not bear investigation ; in cases in which cervical ribs are 

 fully developed, and reach to the sternum, their attachment to the pre- 

 sternum is by means of costal cartilages to the lateral borders of the bone 

 below the articulation of the clavicles.'" 



There is more difficulty in deciding if the ossicles are homologous 

 with shoulder-girdle or sternal elements. Gegenbaur''*" and Parker" 

 both seem to agree that they represent structures which are not, strictly 

 speaking, appertaining to the shoulder-girdle, but are median in position 

 and placed in front of the sternum (inter clavicle and omosternum). 



Parker lays great stress on the morphological distinction between 

 ' membrane ' bones and ' cartilage ' bones in the lower vertebrates, and 

 points out that the shoulder-girdle (scapula, coracoid, and prae-coracoid) 

 and sternum (including omosternum) are cartilaginous in formation ; whereas 

 the clavicle and interclavicle are membrane bones. 



There seems to be a general consensus of opinion regarding the fate 

 and homologies of the elements of the shoulder-girdle. The reptilian 

 coracoid appears to be represented in man by the coracoid process, and 

 possibly also by the costo-coracoid ligament (along with the epicoracoid 

 bone, present in certain mammals (PL X, Fig. 66), such as Mus mus- 

 culus, crocidura (Gegenbaur). The prae-coracoid, extending in reptiles 



