46 HUXLEY, ON THE SKELETON OF FISHES. 
embryo, giving articulation to the lower jaw, which therefore 
is, as in the embryo, only indirectly connected with the so- 
called tympanic cartilage, which again is the homologue of 
the temporal and symplectic. In this respect, as in so many 
others where the skeleton is concerned, the Teleostean em- 
bryo is typified by the adult Elasmobranch and by some 
Ganoids. 
With respect to the homologies of the bones of the fish’s 
face in other vertebrata, the evidence of deyelopment appears 
to me to be no less decisive. No one who compares the 
development of the two will, I think, doubt that in the fish 
Cuvier’s palatine is the homologue of the palatine of the abran- 
chiate Vertebrata, that his pterygoid is the homologue of their 
pterygoid (wholly or in part), and that his jugal is their 
quadratum or incus. The comparison with the development 
of the frog, furthermore, leayes no doubt on my mind that the 
tympanic” of the fish is a dismemberment of the pterygoid, 
and has not the remotest relation with the true tympanic, 
I can, however, find no homologue of the temporal and 
symplectic of the fish in the abranchiate Vertebrata. They 
appear to me to he specially piscine elements, which are 
only traceable as far as the Amphibia, where they are 
represented by that part of the suspensorial cartilage 
(quadrate or tympanic cartilage of authors) to which the 
hyoid arch is attached, and by the “‘ temporal”? of Cuvier. In 
the abranchiate Verterata, if the hyoid 1s connected with the 
skull at all, its imsertion is quite distinct from that of the 
mandibular arch. I believe, therefore, that the branchiate 
Vertebrata, the oviparous abranchiate Vertebrata, and the 
Mammalia, present a series of well-marked gradations in the 
mode in which the ramus of the mandible is attached to the 
skull. In the fish it is separated by the os articulare, the 
quadratum, and the temporo symplectic. In the Amphibia the 
latter becomes less distinct, In the abranchiate Ovipara it 
disappears, but the ramus of the mandible is still separated 
from the skull by the articulare and quadratum. In the 
Mammata, finally, these are converted into the malleus and 
incus respectively, and the ramus comes into direct contact 
with the squamosal element of the skull. 
