218 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvl 



center of the alisphenoid and in front of the pro-otic." Following 

 this definition it locates at once the foramen ovale as the large open- 

 ing (V, fig. 5) between the union of the alisphenoid and prootic, 

 which is lai'gely inclosed by the prootic, the alisphenoid forming only 

 the anterior boundary. In assigning a similarly placed foramen to 

 the third nerve in a skull of Hypsilopfwdon, Hulke* appears to be 

 in error. 



The determinations of the foramina of this region diiler some- 

 what from those of Andrews'' for the skull of Iguanodon, due to the 

 different arrangement of the foramina entering the foramen lacerum 

 posterius, Iguanodon having both an anterior and posterior branch 

 instead of being single as in Cmnptosaurus. 



The pituitary fossa is deep, extending considerably below the floor 

 of the median vesicle. Its ventral posterior angles mark the posi- 

 tions where the internal carotids enter the cavity diagonally from 

 deep external fissures on the sides of the basisphenoid shown at c, 

 fig. 5. 



None of the skulls studied show the relations of the foramina 

 anterior to those for the branches of the trigeminal or fifth nerve. 



It is unfortunate that there is not a brain case sufficiently complete 

 from which a cast of the brain cavity might be made, for it would 

 show at once the great similarity to the brain of Iguanodon as 

 described by Dr. C. W. Andrews. The ventral surface of the 

 supraoccipital of Cat. No. 5473, U.S.N.M., if cast would show the 

 same compressed cerebellum rising high above the hemispheres. This 

 high dorsal development of the brain appears to be peculiar to 

 Oani ptosaiirus and Iguanodon^ although there is a suggestion of it 

 in the brain casts of some of tlie trachodont reptiles. 



THK LOWER JAW, 



A complete jaw of Camptosaurus is unknown, but a study of well 

 preserved parts, representing several individuals which supplement 

 one another, shows that each ramus is formed of seven separate bones, 

 the two rami being joined anteriorly by a predentary. The arrange- 

 ment of the bones of the posterior half of the ramus are admirably 

 shown in No. 1887, Yale Museum (see Plates 8 and 9), and the 

 description of this region is based principally upon a study of this 

 specimen. 



The dentary. — The dentary which forms the anterior half of the 

 jaw is the largest of the elements composing it and bears along the 

 outer part of its dorsal border aveoli for 15 teeth — on the inside 

 16 can be counted (see 2, fig. 8). Anteriorly it is somewhat com- 



« Quart. Journ. Geol. 8oc. London, XXXVI, 1880, p. 4.35. 

 ^Annals and Magazine Natural History, 6th ser., XIX, p. 500. 



