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ERIK A : SON STENSIO 
In Lepidotus the opisthotic might perhaps heve been divided into a ventral and a 
dorsal part, .of which the former would, as in the Teleostei, be fused to the lateral occi¬ 
pital, while the latter would have been distributed over both the prootic and the epiotic 
or eventually only over one of them. 
Instead of the view now put forward it might also be maintained that in several 
of the fishes mentioned the opisthotic might have been reduced, and that its place might 
have been occupied secondarily by adjacent bones. In this way, for instance, one might 
suppose could be explained the extension of the lateral occipital and the prootic in 
Lepidosteus, the lateral occiptal, the prootic and the epiotic in Lepidotus, the prootic in 
the Coelacanthids and the lateral occipital in the Teleostei. With regard to the pterotic 
of the Teleostei one is compelled to assume, if it is desired to carry these views through 
consistently, that the cartilage component of this bone is a new formation. 
It is of course possible that objections of this sort are more or less justified, but 
is seems „difficult to me at present to accept them for the following reasons: 
1) Elements of bones equivalent to the opisthotic of the Tetrapods exist in lower 
Teleostomes, e. g. Polypterus and Birgeria. To assume, under these circumstances, that 
the cartilaginous bone component of the pterotic in the Teleostei would be a new for¬ 
mation, seems to be unjustified so long as no certain evidence of this is put forward. 
2) The conditions in Birgeria which will be described below, seem to indicate the 
way in which fusion between the opisthotic and the membrane bones of the cranial 
roof would have taken place, and how after this the dorsal part of the opisthotic may 
be supposed to have become loosened from the ventral part by mechanical processes. 
3 ) If in connection with the facts mentioned we remember that in Tetrapods (cf. 
Gaupp, 1905, pp. 711—712, 772, 780, 786 etc.; cf. also p. 141 above) the opisthotic is 
often fused with the lateral occipital, we ougth not to find it especially curious that the 
ventral part of the opisthotic may be fused with the lateral occipital in certain of the 
Teleostome fishes. On the other hand there seems to be an example in the Tetrapods 
(cf. p. 141 above) to show that the opisthotic can be fused to the prootic, and so the 
conditions that I think I have found in the Coelacanthids do not seem to be so excep¬ 
tional either as one might perhaps be inclined to think. 
In order now to connect the description with Birgeria mougeoti we find that the 
opisthotic component of the prootico-opisthotic of this fish is presumably pierced by 
n. glossopharyngeus (IX, text fig. 61). It is obvious that this component in its entirety 
corresponds well to the similarly named component in Polypterus. This is also true in the 
main of the epiotic component in the two genera. 
The prootic component in the prootico-opisthotic of B. mougeoti is not particularly 
strongly developed. Forwards it only extends to the facialis canal. Its most anterior 
part is pierced by a fine canal, which rises from the facialis canal and has its exit on 
the dorsal side of the primordial neurocranium under the supratemporo-intertemporal 
antero-medially of the ossification centre of this bone. In my opinion we are probably 
concerned here with the canal for r. oticus lateralis. 
Whether the prootico-opisthotic of B. mougeoti also had any intercalar component 
incorporated with it cannot be established because of the deficient state of preservation 
of the present material. With regard to the very interesting relation between the prootico- 
