174 Dr. T. Gill on the Homologies 



as the coracoid (subject to the proviso hereinafter stated), 

 unless some specific evidence can be shown to the contrary. 

 No such evidence has been jiroduced. 



III. The scapula in the Urodele and other Batrachians is 

 entirely or almost wholly excluded from the glenoid foramen, 

 and above the coracoid. 



Therefore the corresponding element in Dipnoi must be the 

 scapula. 



IV. The other elements must be determined by their relation 

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

 which they originate. 



All those elements in immediate connexion* 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 dismember- 

 ments therefrom the coraco-scapular element than that they 

 have independently originated. 



But the homogeneity 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-girdles of the distantly separated classes may be (to 

 use the terms introduced by Mr. Lankester) homoplastic ; but 

 they are not homogenetic. 



Therefore they must be named accordingly. 



The element of the Dipnoan's shoulder-girdle continuous 

 downwards from the scapula, and to which the coracoid is 

 closely applied, may be named ectocoracoid. 



V. Neither the scapula in Batrachians nor the cartilaginous 

 extension thereof, designated suprascapula, is dissevered from 

 the coracoid. 



Therefore there is an a priori improbability against the 

 homology with the scapula of any part having a distant or 

 merely ligamentous connexion with the humerus-bearing ele- 

 ment. 



Consequently, as an element better representing the scapula 

 exists, the element named scapula (by Owen, Gunther, &c.) 

 cannot be the homologue of the scapula of Batrachians. 



On the other hand, its more intimate relations with the skull 

 and the mode of development indicate that it is rather an 

 element originating and developed in more intimate connexion 

 with the skull. 



* The so-called scapula and suprascapula of most authors are excluded 

 from this connexion. 



