1890.] The Homologies of the Fins of Fishes. 403 
agree in the interpretation of the homologies of these parts, 
but if the view enunciated by Balfour of the origin and 
development of the paired limbs is the correct one, it is pos- 
sible that a homology can be traced 
along the downward scale of limb- 
development from the Batrachia on 
the one hand, and the Teleostomata on 
the other, to the ancestral type of the 
Ichthyotomi of the Carboniferous, the 
oldest limb type known. 
Dr. Gill” traces out the relationship 
of the members of the shoulder-girdle - 
in the Dipnoi with those of the Batra- 
chia as follows: The proximal element 
of the anterior limb of the Dipnoan is 
the homologue of the humerus. In 
the Urodela the humerus is articulated 
chiefly with the coracoid ;. therefore, 
the element of the Dipnoan shoulder- 
girdle with which the humerus is 
articulated is the coracoid, unless evi- 
dence to the contrary can be produced. 
The scapula in the Batrachia is entirely foc iat ela auaa Wes D, 
or almost excluded from the glenoid axial elements; t, radials; F.S, fin- 
foramen, therefore the corresponding ™*? BA VOET 
element in the Dipnoi must be the scapula. The element of the 
Dipnoan shoulder-girdle continuous downwards from the scapula, 
and to which the coracoid is closely applied, is named by Gill the 
ectocoracoid. Each half of the shouldergirdle is surmounted by 
an element which is named the supraclavicle by Gegenbaur, the 
suprascapula by Gunther, the scapula by Owen ; and this is in 
turn connected with the skull by another element, the posttem- 
poral of Parker and Gill, who justly observe that there is an à 
priori improbability against the homology with the scapula of any 
part having a ligamentary connection with the humerus-bearing 
element. 
1 Arrangement of the Families of Fishes, Nov., 1872. Smithsonian Misc. Col., Val. XI. 
LY 
Mf 4 
Ahy f 
UE A 3 
ONRU 
Ss SS 
SSS : 
SS INR PAOL 
SS = ; ASS 


G. 2—Neoceratodus forsterii, 
