Annals of the Transvaal Museum. 
135 
i.e. the right border of the layer is parallel with the inwardly concave 
outer border of the pterygoidal vacuity. The left side has been pressed 
against the left pterygoid, the different elements have thereby become 
disconnected and scattered through the matrix. Some of them have 
suffered a vertical displacement of 15 mm. The front border is rather 
fragmentary, but still it can be seen that the front end narrows down con- 
siderably ; it fully conveys the impression that it terminates at the front 
end of the pterygoidal vacuities. 
Most of the elements of the layer are small, polygonal, thin bones. 
Near the front end of the parasphenoid, however, there are some bones 
which are from three to four times the ordinary size. These have suffered 
some displacement. 
The great majority of these bones have their lower surface covered 
with small teeth of about the same size as those on the pterygoids. Teeth 
were not found on those bones in the hinder processes, which were near 
the extremities of these parts and open to observation. These teeth 
present the same general appearance as those on the pterygoids. They are 
mostly broken off and then generally show a pulp-cavity, which with the 
great majority is not filled with calcite. Probably all these teeth were 
once filled with calcite, which subsequently became dissolved. A few 
teeth have been found, however, which still possessed a calcite filling. 
The outer surface of the teeth shows in some cases a series of fine striae near 
the top ; mostly, however, these could not be discerned. The great majority 
of sections of the teeth do not show any plications whatever of the outer 
tooth substance. The same applies to the small teeth on the pterygoids, 
where only a portion of those with calcite filling show this structure. 
Some of the teeth with calcite filling on the ^small bones also show very 
plainly plications of the outer tooth substance. These small teeth may 
therefore be regarded to have the same structure as those on the ptery- 
goids. 
The original position of this layer of bones cannot be made out with 
certainty. Its present position seems to suggest that it originated in the 
epidermis of the pterygoidal vacuities. It is, however, not impossible 
that this layer has been pressed into its present position during the process 
of fossilization and therefore that it may have originated in the epidermis 
of the ventral surface of the lower jaw. In the last case there would be 
no apparent functional difference between these ossifications and the 
dermal skeleton of other parts of the body. The latter, however, are 
plain dermal scales, while the former are for the great majority covered 
with teeth. These teeth do not possess the simple structure which may 
be expected in protective organs of the epidermis, but they show identi- 
cally the same differentiation as the teeth in the oral cavity. The latter, 
however, have acquired the present structure through functional adaption. 
This again supports the probability that the teeth and ossifications in the 
pterygoidal vacuities originated for the performance of the same functions as 
the other teeth in the oral cavity. As far as I am aware small polygonal 
ossifications in this position have only been found once before in Stego- 
ceplialia. This is in Micropholis Stoivi Huxley ; they were originally 
described as dermal scutes and recently WATSON has again described 
them as such. I am not in a position to state, however, whether the 
ossifications in Micrypholis are Of the same kind as in Myriodon or not. 
To conclude, I may contrast the arguments for and against the above- 
mentioned views in a table. 
