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PROFESSOR H. G. SEELEY ON THE STRUCTURE, ORGANIZATION, 
contour of the palate, upon which the measurements of the bones already described 
are drawn (fig. 2). The orbits of the eyes were possibly larger than here shown, while 
'the posterior border to the orbit is given on the hypothesis that post-frontal and malar 
bones were present, and that the malar united with the maxillary in the usual way. 
There is no evidence whether the malar arch connected with the quadrate bone. 
The characters shown by the skull are not to be found in one order of animals. In 
the first case I will assume that the position of the nares is in the small ant-orbital 
vacuity, and that they were not terminal as in the South African Theriodonts described 
by Sir Richard Owen, and in Ohelonians, or subterminal as in existing Crocodilia and 
Ophidia. There are several fossil types in which the external nares are quite as small 
and have as backward a position. In Pistosaurus from the Muschelkalk both these 
conditions are seen, and in many species of Plesiosaurus the nares, and other vacuities 
of the superior surface of the skull, are similarly placed. In true Plesiosaurians there 
is not the same posterior constriction of the cerebral region, for the brain case is always 
widest in its hinder part. And Plesiosaurs have not the same broad fiat interspace 
between the orbits formed by the frontal bones. But in Nothosaurus from the 
Muschelkalk there is the same posterior divergence of the occipital crest, a similarly 
inclined supra-occipital region, a corresponding posterior attenuation of the brain case, 
which, like the temporal vacuities, is more elongated ; and there is a broad, flattened, 
inter-orbital area in Nothosaurus, though it is relatively smaller than in Protor'osaurus, 
while the orbits are small, the nares relatively large, the snout not pointed, and there 
is a large parietal foramen. Altogether the resemblances are remarkable. The 
resemblances of the palate are less obvious, for no Plesiosaur or Nothosaur at present 
known has a palate which is open in the median line; though, so far as form is 
concerned, the pterygoid bones show some resemblance, and are noticeable for the 
width of the plate which laps along the quadrate bone in Plesiosaurus, though it is 
narrower than in Protorosaurus in proportion as the PlesiosauriaD skull is more 
depressed. 
The resemblance to the skull of Ichthyosaurus, in form, is very close. The orbits 
are behind the middle of the length of the head, and the temporal vacuities and 
nares are similarly situate ; but there is a fundamental difference in the minute size 
of the true frontal bones in Ichthyosaurus, in which genus they are excluded from the 
orbital margin by the intervening nasal, post-frontal, and pre-frontal bones; moreover, 
the nasal bones do not usually extend in Ichthyosaurus nearly to the extremity of the 
snout. If, however, the Ichthyosaurian nasals had extended no further backward than 
in Protorosaurus, they would have come as far forward anteriorly, and if the frontal 
bones had grown to fill the space thus left vacant the post-frontal bones would have been 
pushed outward and backward ; though there can be little probability that the post- 
orbital part of the Protorosaurian skull could have been Ichthyosaurian. On the 
palate the resemblance is greater than among Plesiosaurs, because the palate is open 
in the middle line in Ichthyosaurus and the bones are elongated and taper to their 
