X1Y 



shoulder girdle and its constituents in fishes. But the recent observa- 

 tions of Bruhl, Gegenbanr, and Parker have thrown a flood of light upon 

 the subject. Some minor questions, however, appear still to be unsettled ; 

 the writer, at least, has not been able to convince himself of the correctness 

 of all the identifications, and of the names conferred as expressions thereof. 

 Recent study has increased such doubts respecting the applicability of 

 former nomenclatures, and has led to conclusions different from those 

 announced by previous investigators. 



The following are assumed as premises that will be granted by all 

 zootomists : 



1. Homologies of parts are best determinable, cseteris paribus, 1 in the 

 most nearly related forms. 



2. Identifications should proceed from a central or determinate point 

 outwards. 



The applications of these principles are embodied in the following 

 conclusions : 



1. The forms that are best comparable and that are most nearly related 

 to each other, are the Dipnoi, an order of fishes at present represented by 

 Lepidosiren, Protopterus, and Ceratodus, and the Batrachians as repre- 

 sented by the Ganocephala, Salamanders, and Salamander-like animals. 



2. The articulation of the anterior member with the shoulder girdle 

 forms the most obvious and determinable point for comparison in the rep- 

 resentatives of the respective classes. 



THE GIRDLE IN DIPNOANS. 



I. 



The proximal element of the anterior limb in the Dipnoi has, almost by 

 common consent, been regarded as homologous with the HUMERUS of the 

 higher vertebrates. 



II. 



The humerus in the TJrodele Batrachians, as well as the extinct Gano- 

 cephala and Labyrinthodontia, is articulated chiefly with the coracoid. 



Therefore, the element of the shoulder girdle with which the humerus 

 of the Dipnoi is articulated, must also be regarded as the CORACOID 

 (subject to the proviso hereinafter stated), unless some specific evidence 

 can be shown to the contrary. No such evidence has been produced. 



III. 



The scapula in the TJrodele 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. 



1 Parts affected by teleological modifications may be excepted. 



