NO. 1666. OSTEOLOGY OF CAMPTOSAURUS—GILMO 



teriorl}^ notched process descends to the basisphenoid a 

 with it by a slightly expanded end. The posterior bordt 

 process forms the anterior margin of the foramen ovale u,. 

 transmission of the trig-eminal or fifth nerve (see V, fig. 5.) Above 

 the foramen ovale the alisphenoid is united by suture to the prootic 

 bone, as plainly shown in Cat. Xos. 5473 and 5997, U.S.N.M. Their 

 external surfaces form part of the inner and anterior boundaries of 

 the supratemporal fossa. The alisphenoids in /Stef/osaun/.s appear 

 to be identical in shape, position, and relationship, as regards the 

 surrounding elements. 



Orhitosphenoids. — Ossified orbitosphenoids Avere undoubtedly 

 ])resent, as indicated by two thin, flattened, plate-like elements found 

 in the matrix with the alisphenoids of Cat. No. 5097. U.S.N.M. 

 Furthermore, these appear (if not mutilated) to be large enough' to 

 comj)lete the anterior portion of the brain case, as shown by specimen 

 Cat. No. 5473, U.S.N.M. If present, they would form the walls which 

 enclose the olfactory lobes of the brain. 



The prootic. — Between the occipital and parietal segments of the 

 skull of Camptosaurus is an area which must represent the position 

 of the auditor}^ or periotic capsule. As in most reptiles, the elements 

 forming the cajosules, i. e., the opisthotic and epiotic, are probably 

 fused so that their exact identification is rendered somewhat difficult, 

 the prootic alone remaining differentiated in the adult. 



The prootic, as plainly shown by the two specimens. Cat. Nos. 5473 

 and 5997, U.S.N.M., is bounded as follows: Posteriorly by the 

 opisthotic ; dorsally by the supraoccipital, unless the epiotic be fused 

 with that bone, a jjoint, however, which can not now be determined; 

 anteriorly by the alisphenoid, and ventrally by the basisphenoid. 

 These relations are clearly shown in the specimens studied, as the 

 sutures remain distinct in both. 



In Cat. No. 5997, U.S.N.M., the prootic is all that remains of the 

 lateral walls of the brain case, still attached to the basisphenoid, the 

 alisphenoids, and orbito-sphenoids being present but detached from 

 the rest of the specimen. As shown by a third specimen. No. 5996, 

 U.S.N.M., these elements are united to the basisphenoid antero-pos- 

 teriorly by pit-like, roughly sutured surfaces, but above they expand 

 into a thickened wing-like dorsal portion produced more especially in 

 the posterior direction, which extends backward and outward and laps 

 along the median anterior surface of the outward extension of the 

 opisthotic, uniting by horizontally striated sutural surfaces. Above the 

 large foramen (internal auditory meatus, see VIII, fig. 5), the suture 

 between the prootic and opisthotic is nearly vertical up to the back- 

 ward projection of the former. The dorsal surface is united by an 

 inclined sutural surface (see s, fig. 5) with the overlying supra- 

 occipital. The figure shows the supraoccipital crushed upward from 

 Proc. N. M. vol. xxxvi — 09 14 



