218 REPORT—1846. 
trosal, ‘rocher*.’ But the real difficulties which beset the quest of general 
truths in comparative osteology are such that we may well dispense with any 
over-statements of the amount of deviation from the cranial archetype which 
much-modified skulls like those of the anourous batrachia may present. 
Fortunately the light which the development of such skulls throws upon 
their mature characters, is aided by the persistent larval stages manifested 
by the perennibranchiate species. 
In the menopome, for example, the prefrontals remain distinct, both from 
each other and from the orbitosphenoids+, their characteristic connections 
and functions being the same as those of their coalesced homologues in the. 
frog, except that they are notched, instead of being perforated by the olfac- 
tory nerve, which grooves their inner border, as in ‘the cod and some other 
fishes. Cuvier just hints at the possibility of his ‘os en ceinture’ in the frog 
representing “a la fois le frontal principal et l’ethmoide},” or as having an 
equal pretence to one or the other name. 
The suture, however, which marks the limits between the frontal 11 and: 
parietal 7 is persistent in the menopome, and indeed. in all batrachians but 
the anourans; and even in the very young larve of these, Cuvier admits 
(and the observations of M. Dugés warrant the admission ) * que l’on sépare 
une partie postérieure de forme ronde de l’antérieure qui est allongée” (Jbid. 
p- 387). The permanently distinct frontals present a similarly elongated form 
in the urodeles, and are therefore recognized by. Cuvier in the salamander, 
e.g. at ¢, pl. xxv. fig. 1, op. cit.; in the newt, pl. xxvi. fig. 6 ; in the menopome, 
fig. 4; in the axolotl, pl. XXVii. fig. 24; in the siren, 7b. fig. 2; and in the am- 
phiuma, ib. fig. 6. In all these crania the true frontals are indicated by the 
same letter ¢; in none of them do they close the cranial cavity or bound the 
orbits anteriorly, or are perforated by the olfactory nerves, or articulate with 
the vomer below, or perform any of the essential functions, or combine the cha- 
racteristic connections of the prefrontals of fishes, all of which concur in the 
‘os en ceinture.’ But the frontals do present the chief connections and occupy 
the relative position of the anterior half of the bone (11—, fig. 13) which 
Cuvier calls the parietal in the frog. The evident tendency to coalescence of 
essentially distinct bones which pervades the skeleton in the adult anourans 
greatly diminishes the difficulty, through the loss of the suture between the 
parietal and frontal, of recognizing the homology of the latter bone, which, 
with that exception, not only repeats the characters of the frontals in fishes, 
but of those in most tailed batrachians. 
Next, then, with regard to the ethmoid, the second of the two bones to 
which Cuvier restricts the choice of the homologues of the ‘os en ceinture,’ 
no. 14. No name has been applied more vaguely or with a less definite 
meaning than this same ‘ethmoide.’ In the sense in which Cuvier would 
permit its application in the present instance, it is a bone which forms the 
* Op. cit. p. 386. 
+ The menopome, which represents a gigantic tadpole of the tailless batrachia, manifests 
a. beautiful conformity to the general type, and well illustrates the real nature of the apparent 
deviations which take place in the course of the remarkable metamorphoses of the anourans. 
At first sight the orbitosphenoids seem to be barred out from their normal connection with 
the frontal by the junction of the parietal with the prefrontal in the menopome, as appears, 
for example, i in the figure given by Cuvier in the ‘ Ossemens Fossiles,’ v, pt. ii. pl. Xxvi. fig. 4, 
where c’ h divides ec from u. Remove, however, the prefrontal h from the parietal e ’ (which 
may be readily done, the suture, which i is not indicated in the figure cited, being persistent), 
and the anterior and mesial half of the orbitosphenoid (z) is then seen extending inwards 
(mesiad), beneath the parietal and prefrontal, to join a triangular surface formed by a de- 
scending process from the middle of the outer edge of the frontal. 
t Op. cit. p. 388. 
