I 



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



PremaxiUary. — Two specimens, Nos. 1880 and 1887, Yale Museum, 

 have the premaxillae preserved, and the following description is 

 based upon their study : 



In Camptosaunis the premaxillse are edentulous. The dentigerous 

 surface anteriorly is expanded transversely, but posteriorly it con- 

 tracts and sends backward and upward a thin, flat process which is 

 intercalated between the maxillary and nasal. The posterior termina- 

 tion appears to reach the prefrontal and has been so indicated in the 

 restoration shown in fig. 2. I am inclined to believe it did not ex- 

 tend quite so far posteriorly as Marsh has indicated in his recon- 

 struction of the skull. 



A regidarly curved subtriangular process rises from the antero- 

 superior surface and forms the upper boundary of the narial orifice. 

 Medially it is closely applied to its fellow of the opposite side but 

 not ankylosed. Thickened below, it gradually tapers upward to a 

 point which meets the anterior extremity of the nasal at the summit 

 of the external nares. The external surface of this process is very 



rugose and, like the rostral 

 ^,-'''',.'-'' bone of TriceratopSj was 



doubtless covered with a 

 horny sheath which opposed 

 a like covering over the 

 predentary. At the base of 

 this superior process is an 



Fig. G. — Outline of left ruEMAxiLLARv of ^,^„i 4!„„„,„„„ /^^^ G~ a ■f\ 



„ ,, ,., ioD« oval loramen (see tig. b, / ), 



Camptosaurus medius Maush. No. 1880, _ _ ^ & 5 //? 



Yale Museum ; 1 nat. size. Holotype. a, wllicll pierces the bone, and 



^'''ir.'r.TT;^™'''''''''""'''^'^''^'''^''^' appears on the ventral sur- 



P, POSTEKIOU END. i ^ 



face. The left premaxil- 

 'ary of No. 1880, Yale Museum, has a dentigerous surface 51 mm. 

 in length. The greatest w^idth of the expanded ends of the premax- 

 illae in this specimen is 41 mm. On either side of the median junc- 

 tion of the anterior ends are small rounded protuberances, separated 

 medially by a shallow cleft. 



The principal characters of the premaxillary are well shown in 

 Plate 7, fig. 1. 



The maxUlary. — As shown in fig. 7, the general outline of the 

 maxillary is that of an irregular triangle. Dorsally it develops a 

 slender, backwardly directed process which, in No. 1886, Yale Mu- 

 seum, rises to a height of 59 mm. above the external dentigerous 

 margin. From the posterior base of this ascending process, the 

 upper border gradually descends to 20 mm. above the last tooth. 



Throughout nearly the whole length of the external surface, some 

 10 to 12 mm. above the border, the maxilla is pierced by a series of 

 foramina. None of these, however, lead into the dental chamber but 

 are received in a large, elongate cavity situated at the base of the 



