62 
FOSSIL REPTILIA OF THE 
frontal (PL XX, 12) is undoubtedly interposed between the bone I determine as ‘ mastoid ^ 
(ib. 8) and the orbit (ib. o) ; and my ‘ mastoid ’ in Pterosauria answers to Cuvier’s and 
Hallman’s ‘temporal,’ i.e. squamosal, in Birds. We may conclude, therefore, that Von 
Meyer’s ‘ Schlafenbein ’ in Pterosauria is that marked 8 in the skull of Pterodactylus 
crassirostris} 
Certain it is that no bone answering to 8 in Pis. XVII, XVIII, XX of the present 
Monograph contributes to the formation of the orbit in any Bird. In the great majority of 
that class, as is well known, the rim of the orbit is incomplete below ; it is formed above 
by the frontal, before by the prefrontal and lacrymal (‘ antorbital ’ of ornithotomists), 
behind by the postfrontal (‘postorbital,’ ib.). Where, as in some Psittacidee,^ the orbital 
rim (‘ Augenhohlenrandes ’) is complete, the lower complement is formed by an extension 
of ossification from the antorbital to the postorbital processes, independently of either 
Cuvier’s temporal (8) or my squamosal (27) in Birds. 
I confess that the foregoing result of the analysis of a main ground of Von Meyer’s 
assertion as to the “ incontestable similarity between the Pterosaurian and Avian types of 
cranial structure ” has not a little tended to shake my confidence in the grounds on which 
he has pronounced definite judgment on the matter. So far as we have yet got evidence 
of the structure of the skull in Pterosauria, it seems that, contrary to the rule in Birds, 
the orbital rim is entire ; and that its lower border is completed by the zygomatic arch, and 
chiefly, if not exclusively, by the malar element ; whereas, such arch passes freely beneath 
the orbital rim in the few Birds with that rim entire. Now, in this part of the cranial 
structure the Pterosauria agree with the Crocodilia : as in them the malar (26) sends up a 
process to unite with one descending from the postfrontal ( 12 ) to complete the orbital 
rim behind. 
In the small species of Pterodactyles [Pt. longirostris, Pt. scolopaciceps, and in the 
perhaps immature animal represented by Pt. brevirostris) the hind convexity of the cranial 
wall is not marked by the apophysiary developments of paroccipital and mastoid, and 
accordingly resembles that part of the cranium in Birds, especially the smaller Gratia ; but 
before this similarity of shape can be pressed into the argument for the Avian affinity of 
the Pterosauria, it should be shown to be common to or constant in the extinct volant 
order. 
Blit this is far from being the case. When a Pterosaur has gained the size of 
Pterodactylus crassirostris ® or Pter. suevicus,^ the back of the skull shows no cerebral 
swelling, but only the crests and processes for muscular attachments, as in other Beptilia 
1 ‘ Monograph on Fossil Reptilia of the Cretaceous Formations ’ {Pterosauria) (1851),’ PI. XXVII, 
figs. 3 and 4. 
^ ‘On the Archetype and Homologies of the Vertebrate Skeleton,’ 8vo, 1848, pi. i, fig. 1 {CaJypto- 
rhijnchus) ; ‘Anatomy of Vertebrates,’ 8vo, vol. ii (1866), p. 51, fig. 30 {Psittacus'), also p. 63. 
3 Goldfuss, op. cit., pi. vii. 
Quenstedt, op. cit. 
