Morphology of the Fins 87 



the coracoid. Therefore the corresponding element in Dipnoi 

 must be the scapula. 



" The other elements must be determined by their relation to 

 the preceding, or to those parts from or in connection with 

 which they originate. All those elements in immediate connec- 

 tion with the pectoral fin and the scapula must be homologous 

 as a whole with the coraco-scapular plate of the Batrachians; 

 that is, it is infinitely more probable that they represent, as a 

 whole or as dismemberments therefrom, the coraco-scapular ele- 

 ment than that they independently originated. But the homo- 

 geneity of that coraco-scapular element forbids the identification 

 of the several elements of the fish's shoulder-girdle with regions 

 of the Batrachian's coraco-scapular plate. 



" And it is equally impossible to identify the fish's elements 

 with those of the higher reptiles or other vertebrates which have 

 developed from the Batrachians. The elements in the shoulder- 



FIG. 73. Clavicles of a Sea Catfish, Selenaspis dowi (Gill). 



girdles of the distantly separated classes may be (to use the 

 terms introduced by Dr. Lankester) homoplastic, but they are 

 not homogenetic. Therefore they must be named accordingly. 

 The element of the Dipnoan's shoulder-girdle, continuous down- 

 ward from the scapula, and to which the coracoid is closely 

 applied, may be named ectocoracoid. 



" Neither the scapula in Batrachians nor the cartilaginous 

 extension thereof, designated suprascapula, is dissevered from 

 the coracoid. Therefore there is an a priori improbability 



