1G4 Kefout H. A.A. Al)s axck.ment of .Science. 



When we come to the consideration of the anterior coracoidal bar 

 we again find a diff'erence of opinion, but here eacli view has really 

 something that can be legitimately argued in its favour. The only 

 views that we need consider are (1) that of Parker, which is that the 

 whole bar is prfcoracoid, and (2) that of most other writers, who believe 

 that the ossified part is the clavicle. If the girdle of the tadpole be 

 examined, it is found that the antei'ior bar is originally entirely cartila- 

 ginous, and in this condition no oae seems to object to its being called 

 precoracoid : but later on a superficial ossification is formed in front, 

 which clasps and protects the cartilage behind. This bony element is 

 belie\ed to be the clavicle, and the cartilage only is looked upon as 

 precoracoid. Those who hold this second view advance the argument 

 that the clavicle in the mammal is formed in a somewhat similar way. 

 It is held that before the clavicle ossifies there is a cartilaginous bar, 

 whicli is replaced by the developing clavicle, and the tips of cartilage 

 seen on the ends of the bone during growth are shown as petitions of 

 the precoracoid not yet replaced. For the view that the mannnalian 

 clavicle replaces the precoracoid we are indebted to Gegenbaur, who 

 believed that he observed a cartilaginous bar being replaced by the 

 bony clavicle. The methods of research employed in 1864 were not 

 such as could satisfactoril}^ settle such a point, but modern methods 

 sliow that Gegenbaur's obser\ation was incorrect. In marsupials th,ere 

 is no trace of a cartilaginous basis for the clavicle, and there is no 

 cartilage even at the ends of the bone till fairly late in development. 

 In higher mammals cartilage develops on the ends at an earlier period, 

 but never till the clavicle has been ossified for a considerable time. 

 Parker thought the clavicle in the mole was in part coracoid, as the 

 bone seemed almost embedded in cartilage ; but when the earlier stage 

 is studied b}^ modern methods it is seen that the clavicle is a pure 

 membrane bone with no trace of cartilage in connection with it to 

 begin with. AVe can now be quite certain that the mannnalian 

 clavicle, like the reptilian, is a pure membrane bone which has 

 nothing whatever to <lo with the precoracoid. The cartilaginous tips 

 have no more morphological importance than the cartilage found in 

 connection with many other membrane V)ones, such as the frontal, the 

 premaxilla, ite. 



But, notwithstanding, may not the ossificatiijn in the frog be 

 clavicle ? The phylogeny of the frog is not very fully known, but 

 we are probably safe in conctluding that the ancestor was a Stego- 

 cephalian allied to Proiritou. Now, here, as in all Stegocephalians 

 with well-developed limbs, there is an intcrclavicle and a pair of 

 clavicles. These are for tlie most part ({uite superficial, anil the 

 pectoral nuiscles must have been intei'nal to them. When we turn 

 to the modei'n degenerate descendants we find certainly no trace of 

 the interclaviclc. and underneath the skin we see only the broad 

 pectoral muscles, ;aid the supposed clavicle is deep down underneath 

 and completely hidden from \iew. It seems to me extremely im- 

 probable that the clavicle could have had such a migration. We 

 know pretty fully the evolution of the clavicle from the >St<>go- 



