HUXLEY, ON THE SKELETON OF FISHES. 45 
ends above in a free point. The posterior is continuous 
with the cranial wall above, but ends below in a free 
point immediately behind the condyle. The posterior edge 
of this last portion (which I shall term the hyo-mandibular 
cartilage, as it is the means of suspension of both hyoid and 
mandibular arcs to the skull) has, above, a rounded condyle 
for the operculum, while below this, it gives attachment to 
that cartilage which eventually becomes the styloid element 
of the hyoidean are. That part of the cartilage which lies 
above the attachment of this element becomes, by its ossifi- 
cation, the “ temporal’? of Cuvier; that which lies below it 
gives rise to Cuvier’s “‘ symplectique.” 
The anterior division of the posterior crus, the condyle, 
and the anterior crus of the inverted arch I have mentioned, 
constitute a inverted V-shaped ‘ palato-quadrate” cartilage, 
The anterior part of the anterior crus ossifies, and becomes 
Cuvier’s “palatine; the posterior part gives rise to his 
‘transverse’ and ‘ pterygoid ;” the condyloid portion, when 
ossified, becomes his “jugal;” and the extremity of the 
ascending process from this or the anterior division of the 
posterior crus becomes his “ tympanique.” 
The operculum, suboperculum, interoperculum, and pre- 
operculum, are developed in the branchiostegal membrane 
apart from the other bones. 
These embryological facts are of great importance, as they 
enable us to understand, on the one hand, the different 
modifications of the palato-suspensorial apparatus in fishes, 
and on the other hand, the relations of the components of 
this apparatus to the corresponding parts in other Vertebrata. 
They explain, in the first place, the fact to which Kostlin 
first drew attention, that in the Teleostean and Ganoid fishes 
there is every gradation, between the most intimate con- 
nexion of the “ temporal” and “symplectic” with the other 
bones, and their wide separation. They enable us to under- 
stand why, in Lepidosteus, for example, the “jugal”’ remains 
firmly united with the representatives of the “ pterygoid” and 
“tympanic,” while it is connected with the ‘ temporal”? and 
“symplectic”? only by the preoperculum; and they prove 
that the suspensorial apparatus of the sturgeon answers to 
the temporal and symplectic of other fishes, while the carti- 
laginous arch to which its mandible is articulated corresponds 
with the palato-quadrate arcade of the embryo. Again, to 
my mind, they prove that Cuvier was right in denying the 
homology of the so-called upper jaw of the Elasmobranchi 
with the maxilla and premaxilla of a Teleostean ; for it corre- 
sponds precisely with the palato-quadrate arcade of the 
