248 Mr. C. W. Andrews on the Structure 
which will be described on a future occasion. That these 
apertures are the true internal nares there can be no doubt, 
since their relations to the surrounding bones are exactly 
similar to those found in Nothosaurus, according to the 
descriptions and figures of Koken and Lydekker. Moreover, 
their position is essentially similar to that of the internal nares 
in Sphenodon and many Lacertilia. In the former, indeed, 
the skull presents several striking resemblances to that of 
Peloneustes, e.g. in the relations of the vomers, palatines, and 
pterygoids to one another. 
In his paper on Plestosaurus Etheridgei Huxley stated that 
he believed that these posterior fosse (7. e. the posterior pala- 
tine vacuities) had been mistaken for the posterior nares, 
which were really situated much farther forward; and the 
position of these apertures was correctly determined by Sollas 
in Plesiosaurus megacephalus. He, however, describes the 
whole of the plate of bone behind the vomers as palatines, the 
suture between these bones and the pterygoids being either 
obliterated or really represented by the fissures, which he 
states “might easily be mistaken for sutures,” and which 
occur exactly where the junction between the palatines and 
the anterior wing of pterygoids might be expected to be 
found: if we accept this last alternative as the correct one, 
the pterygoids met the vomers in the genus Plesiosaurus 
also; the form of the hinder border of the united vomers 
would lead one to suspect that this was the case even if no 
trace of suture were visible. The same arrangement has 
been recorded by Lydekker in the case of Plesiosaurus dolicho- 
dirus, 
The pterygoids (woodcut 1, pt., p. 245), the largest bones in 
the palate, are peculiarly complex. ‘They may be described as 
triradiate bones, each consisting of an anterior, a lateral, and 
a posterior ramus. The anterior ramus terminates in front 
against the vomer ; externally it is bounded by the palatine, 
the suture with which at first runs str aight backwards, then 
curves outwards (see woodcut 1), after wards resuming its back- 
ward course as far as the hinder border of the palatine, at 
which point the pterygoid is about twice as wide as it is 
opposite the posterior end of the vomers. 
The anterior border of the lateral pterygoid ramus is nearly 
straight and unites with the hinder margin of the palatine 
in a suture which runs at right angles to the axis of the skull. 
Its outer margin joins the transpalatine (ectopterygotd) in 
a somewhat complicated suture, which first runs backwards 
and inwards, then turns sharply outwards and cuts a large 
oval tuberosity with a truncate rugose extremity, so that 
