"The humerus of Urodele Batrachians, as well as the extinct Ganocephala 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.
"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.
"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 connection 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 element than that they 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.
Fig. 73.—Clavicles of a Sea Catfish, Selenaspis dowi (Gill).
"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 Dr. Lankester) homoplastic, but they are not homogenetic. Therefore they must be named accordingly. The element of the Dipnoan's shoulder-girdle, continuous downward 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 against the homology with the scapula of any part having a distant and merely ligamentous connection with the humerus-bearing element. Consequently, as an element better representing the scapula exists, the element named scapula (by Owen, Günther, etc.) 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 connection with the skull. It may therefore be considered, with Parker, as a post-temporal.
"The shoulder-girdle in the Dipnoi is connected by an azygous differentiated cartilage, swollen backwards. It is more probable that this is the homologue of the sternum of Batrachians, and that in the latter that element has been still more differentiated and specialized than that it should have originated de novo from an independently developed nucleus."
Fig. 74.—Shoulder-girdle of a Batfish, Ogcocephalus radiatus (Mitchill).