m 



208 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. " 



stricted, while the outer termination is expanded both dorsally and 

 ventrally, more especially in the latter direction, into a wide, some- 

 what broadly rounded end. The posterior surface of this process is 

 gently convex dorso-ventrally, while the anterior surface is plane, 

 with a shallow, longitudinal groove extending for part of its length 

 on the anterior inferior border. 



Supraoccipital. — The supraoccipital of Camptosanrns, as in the 

 English Hi/psilophodon and Camptosarirns prestunchn, enters into 

 the formation of the boundary of the foramen magnum. It con- 

 tributes to the upper median boundary, and extends forward and 

 upward into a stout pyramidal median crest, which is inclosed dor- 

 sally and laterally by the parietals. Ventrally it articulates by heavy 

 sutured surfaces with the obliquely placed dorsal faces of the ex- 

 occipitals and prootics. The principal characters of this bone and 

 the relation it bears to the surrounding elements of the skull are 

 clearly shown in figs. 4 and 5. 



Basispheiioid and pciraspheno'ul. — The basisphenoid is very heavy 

 and broad posteriorly where it articulates with the basioccipital by 

 a deep vertical suture. On its posterior ventral surface two heavy, 

 roughened buttresses are developed, Avhich slightly underlap the 

 anterior end of the basioccipital, and between which is received a 

 heavy, median, tongue-like prolongation of the basioccipital. An- 

 teriorly it is narrower and gives oif a pair of diverging processes or 

 pillars, produced somewhat below the ventral surface. These are di- 

 rected downward, backward, and outward, and present in front at 

 their extremities, surfaces for contact with the pterygoids (see ^, pt^ 

 fig. 5). Latere- ventrally the basisphenoid is compressed, having later- 

 ally, one on either side, two forwardly directed slits, from which two 

 converging foramini extend forward into the pituitary fossa. These 

 foramini probably transmitted the carotid arteries, as in the croco- 

 dile (see c, fig. 5). They are also present in Tricerdtops., Stego- 

 saurus, and Iguanodon. Dorso-laterally the basisphenoid articulates 

 with the exoccipital, prootic, and alisphenoid. The parasphenoid ex- 

 tends forward from the base of the pituitary fossa as a median pro- 

 longation of the basisphenoid and divides the interpterygoid vacuity 

 posteriorly into two parts. Its anterior extent, however, can not be 

 determined from available material. 



Alisphenoids. — The alisphenoids are a ])air of roughly triangular 

 bones which arise from the anterior dorsal surface of the basi- 

 sphenoid, and unite dorsally as in the crocodile with the parietal, 

 frontals, and postfrontals (see fig. 5). Their inner surfaces form 

 the walls of that part of the brain case which lodges the cerebral 

 hemisphere. Their anterior ends are divergent, turning decidedly 

 outward, their dorsal surfaces being received in a transverse groove 

 on the anterior ventral surface of the postfrontal. A narrow, pos- 



