6O2 THE NATURE OF THE CLAVICLE. 



bounding these fenestrae both in the scapula and coracoid 

 regions have received special names ; the anterior bar of the 

 coracoid region, forming the prsecoracoid, being especially 

 important. At the boundary between the scapula and the 

 coracoid, on the hinder border of the plate, is placed the glenoid 

 articular cavity to carry the head of the humerus. 



The grounds of difference between Gotte and Hoffmann and 

 other anatomists concern especially the clavicle and inter-clavicle. 

 The clavicle is usually regarded as a membrane bone which may 

 become to some extent cartilaginous. By the above anatomists, 

 and by Rathke also, it is held to be at first united with the 

 coraco-scapular plate, of which it forms the anterior limb, free 

 ventrally, but united dorsally with the main part of the plate; 

 and Gotte and Hoffmann hold that it is essentially a cartilage 

 bone, which however in the majority of the Reptilia ossifies 

 directly without passing through the condition of cartilage. 



The interclavicle (episternum) is held by Gotte to be 

 developed from a paired formation at the free ventral ends of 

 the clavicles, but he holds views which are in many respects 

 original as to its homologies in Mammalia and Amphibia. Even 

 if Gotte's facts are admitted, it does not appear to me necessarily 

 to follow that his deductions are correct. The most important 

 of these is to the effect that the dermal clavicle of Pisces has no 

 homologue in the higher types. Granting that the clavicle in 

 these groups is in its first stage continuous with the coraco- 

 scapular plate, and that it may become in some forms carti- 

 laginous before ossifying, yet it seems to me all the same quite 

 possible that it is genetically derived from the clavicle of Pisces, 

 but that it has to a great extent lost even in development its 

 primitive characters, though these characters are still partially 

 indicated in the fact that it usually ossifies very early and 

 partially at least as a membrane bone 1 . 



In treating the development of the pectoral girdle systematically it will be 

 convenient to begin with the Amniota, which may be considered to fix the 

 nomenclature of the elements of the shoulder girdle. 



1 The fact of the clavicle going out of its way, so to speak, to become cartilaginous 

 before being ossified, may perhaps be explained by supposing that its close connection 

 with the other parts of the shoulder girdle has caused, by a kind of infection, a change 

 in its histological characters. 



