Monograph on Dimorphodon. 133 
When this ring is found, it either consists of a single smooth 
piece (Pterodactylus scolopaciceps, P. crassirostris) or is made 
up of small plates, which lie over each other, and whic may 
be either smooth (Pterodactylus Kochi) or granulated (F: 
eyert). 
“The nostril was double, and often distinguished by its 
large size. The two holes, however, were not separated inter- 
sally, by a partition of a partly bony consistence, as Oken 
cut out. This bone, like most of the skull-bones of the Ptero- 
dactyles, is very thin. But as the intermaxilla ridge, which 
overlies it and extends to the principal frontal bone, is con- 
siderably thicker, as is also the lower margin of the jaw 
which in that part is generally provided with teeth, it could 
not but happen, owing to the pressure to which these petrifac- 
tions have been subjected, that the thin exterior bone received 
a more depressed position in comparison with its borders. It 
thus acquired the appearance of a thin bony partition in the 
inside of the skull. 
in P. brevirostris and P. Meyeri. 
opening is only partially separated by bones from the Dok 
and varies in size according to the distance of the prefront 
from the lachrymal. These two bones are sometimes so near 
together, that the middle hole seems scarcely developed, or 
may even not be noticed at all, as, for instance, in £. Kochi ; 
and P. longicollum and P. rhamphastinus may justify the con- 
viction that there are Pterodactyles which rely have no 
| . Where the middle hole is completely bordered 
by bones, the separation between it and the orbital cavity is 
t by the maxillary. ; 
oniy to a yery Ambient PY is the quadrate, to which 
ulates. Th not. 
birds, but cylindrical and shaft-like, which circumstance was 
