ORNITHOSAURIA. 225 



symphysis. The investing bones of the temporal region, how- 

 ever, do not disappear to the extent observed in birds, there 

 being always an upper as well as a lower temporal arcade ; and 

 the large quadrate bone is firmly fixed, both at its upper end 

 and against a buttress of the pterygoid. There is no pineal 

 foramen. The orbit is very large, and the eye is usually sur- 

 rounded by a ring of sclerotic plates ; the external narial 

 opening on each side is separated from the orbit by an antor- 

 bital vacuity, with which it may be confluent. The posterior 

 nares (known only in Scaphognathus purdoni and Rhampho- 

 rhynchus) are not covered with a secondarily-developed palate, 

 but the narrow vomer separating them is raised far above the 

 plane of the roof of the mouth formed by the premaxillae and 

 maxillae. The basipterygoid processes of the basisphenoid are 

 excessively elongated, to reach the very slender pterygoids, 

 which are separated by a large inter pterygoid vacuity through- 

 out the greater part of their length, but meet in front where 

 they articulate with the vomer. The brain (best known from 

 the natural cast in Scaphognathus purdoni) is remarkably 

 bird-like, but is very small in proportion to the size of the 

 skull. The large optic lobes are visible from above, but seem 

 to have been separated by a forward extension of the cerebellum ; 

 and there is distinct evidence of the flocculus on each side of 

 the medulla oblongata. The teeth, when present, are always 

 restricted to the margin of the jaws ; they are simply conical in 

 form, fixed in a series of complete sockets, and usually more or 

 less irregular in arrangement. The presacral vertebrae are 

 procoelous, and the cervicals are longer than the dorsals ; the 

 sacrum comprises from three to six vertebrae, usually fused 

 together ; and the caudal vertebrae are amphicoelous. The 

 cervical and anterior dorsal ribs are double-headed. The 

 clavicular arch is wanting, but there is a large keeled sternum, 

 with which the slender coracoids articulate by a synovial joint ; 

 the scapula is long and slender. The humerus is short and 

 much expanded proximally ; the radius and ulna are longer and 

 about equal in stoutness. The carpus varies considerably in 

 the number of its elements ; some Jurassic genera exhibit two 

 proximal and four distal bones, while certain Cretaceous forms 

 w. 15 



