106 ON THE ORGANIZATIOlSr OF THE OEinTHOSATJEIA. 



remained unknown, the forms of the bones would have been suffi- 

 cient to show that in their osteology Ornithosaurs resemble birds 

 more closely than other animals ; and that the differences from 

 birds in osteology are much less than the differences between the 

 geveral orders of mammals or of reptiles. 



(3) That the resemblances to reptiles do not necessarily indi- 

 cate genetic affinity with reptiles, any more than the resemblances 

 to mammals indicate mammalian affinities ; and that it is more 

 than probable that both kinds of resemblances are to be ranked 

 among the ordinal rather than with the class characters of the 

 group. 



(4) That the osteology, being largely avian, is in entire harmony 

 with the indications of the soft organs, and justifies the con- 

 viction that the pneumatic foramina seen in the bones served 

 identical purposes in living birds and in these animals, and there- 

 fore that Ornithosaurs form a group of birds which bears relation 

 to existing birds such as the Chelonia hold to the Crocodilia 

 among reptiles. That is, Pterodactyles are birds in the large 

 sense of the term, in some respects much more reptilian than any 

 birds which now survive. 



Hereafter perhaps it may be found desirable to group Ornitho- 

 saurs with the Dinosauria and Dicynodontia in the class Palseo- 

 sauria instituted by Yon Meyer for those extinct orders which 

 hold places intermediate between the higher vertebrata ; but in the 

 met.n time they may well rest near to birds. 



DESCEIPTION OF PLATE XI. 



Pig. 1. Brain of Owl (Sirix oius), seen from above, after Leuret. 



Fig. 2. Natural mould of the upper part of the brain-cavity of an animal from 

 the Cambridge Upper Greensand, referred to Orniihocheirus, show- 

 ing the cerebellum (cm) between and behind the cerebral hemispheres. 

 Portions of the cranial bones in the squamosal regions (s) are left 

 attached to the mould. Nat. size. 



Fig. 3. Inferior aspect of the same specimen, showing the oblong mass of the 

 cerebellum (cm) extending between (s) the lateral bones of the 

 hinder part of the brain-case and (e) the back of the orbit of the 

 eye. Nat. size. 

 Fig. 4. Transverse vertical section through the parietal segment of the skull of 

 an Ornithocheims in the Woodwardian Museum, showing the posi- 

 tion of the optic lobes (o) relatively to the cerebrum (c). 

 Fig. 5. Transverse vertical section through the skull of an owl in the parietal 

 region, for comparison with the preceding figure of an Ornithosau- 



