268 THE ANATOMY OF VEETEBEATED ANIMALS. 



or seven in number, liave low, or obsolete, spinous processes ; 

 and, like tbe vertebr?e of tbe rest of the spine, are procoelous, 

 and bave the neuro-central suture obliterated. The exist- 

 ence of cervical ribs is doubtful. From fourteen to sixteen 

 vertebrae intervene between the cervical and the sacral 

 regions ; and not more than one or two of the hindermost 

 of them, if any, are devoid of ribs. The number of vertebrae 

 ankylosed together to form the sacrum, is not fewer than 

 three, nor more than six. 



The tail is very short in Pterodactylus, and, in this genus, 

 all the vertebrae are moveable upon one another; but, in 

 RhampJiorliynchus, it is extremely long, and the vertebrae are 

 immoveably fixed by what apjDear to be ossified ligamentous 

 fibres. 



The vertebral ribs are slender, and the anterior ones, at 

 any rate, have distinct capitula and tuberciila. There are 

 ossified sternal ribs, and splint-like abdominal ribs. The 

 sternum is broad, and, unlike that of other Heptilia, is veiy 

 completely ossified, and bears a strong median crest on the 

 anterior part of its ventral surface. No median posterior 

 prolongation has been observed in connection with it. 



The brain case is more rounded and bird-like than in the 

 other Reptilia, and, in many other respects, the skull ap- 

 proaches that of birds. Thus, the occipital condyle is on 

 the base of the skull, not on its posterior face ; the cranial 

 bones ankylosed very early; the orbits are very large, and the 

 external nares are situated close to them. The premaxillae 

 are very large, the maxillae slender, and the dentary pieces 

 of the mandible are fused together into one bony mass, with- 

 out any trace of a symphysial suture. 



The resemblance to birds is still further increased, in 

 some species, by the presence of wide lachrymo-nasal fossae 

 between the orbits and the nasal cavities, and by the pro- 

 longation of the extremities of the premaxillae and of the 

 symphysial part of the mandible into sharp, beak-like pro- 

 cesses, which appear to have been covered with horny 

 sheaths. But the reptilian type is kept up by the presence 

 of a distinct postfrontal, which unites with the squamosal, 



