220 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



anterior end, commencing dorsally just anterior to the aveoli of the 

 most anterior tooth, and terminatino- ventrally in a point above the 

 lower border of the dentary. A concave ventral surface posterior to 

 the anterior point or i^rojection on the inward extension of the den- 

 tary, for cartilaginous union with its fellow of the opposite side, ap- 

 parently represents a surface for the reception of a posterior branch 

 of the predentary after that found in Stegosaurus and Triceratops. 



On the outer side of the dentary, about 20 mm. below the superior 

 border, there is a series of foramina that extends the length of the 

 bone. These doubtless served for the transmission of nerves and 

 nutrient blood vessels to the lips. 



The largest foramen on the external surface near the lower anterior 

 end of the dentary at ?n, 1, fig. 8, probably represents the mental 

 foramen through which a branch of the fifth nerve emerges. 



The more important characters of the dentary of C amptosaurus 

 are well show^n in fig. 8, drawn from the left dentary of No, 1886, 

 Yale Museum. 



Surangula7\ — Externally the surangular meets the dentary and 

 coronoid (?) just posterior to the coronoicl process by a nearly verti- 

 cal suture, and forms the upper border of the jaw, extending back- 

 ward and downward to its posterior extremity. Ventrally it unites 

 for its full length with the superior border of the angular. Its 

 upper posterior surface is excavated and forms the external part of 

 the cotylus for the articulation of the quadrate. There is a pro- 

 nounced external mandibular foramen (see s/, fig. 2) on the outer 

 median surface just posterior to its union with the dentary, as in 

 Triceratops prorsus and I guanodon bemissartensis. 



Angnlar. — The angular forms the low'er portion of the posterior 

 third of the ramus, being wider in front than posteriorly. On the 

 external surface, anteriorly, it is overlapped by a broad, thin, pos- 

 terior finger-like prolongation of the dentary, as shoAvn in figs. 1 and 

 2, Plate 8. Dorsally it meets the surangular and prearticular, and 

 in conjunction Avith these elements, inclosed and held in position the 

 small, block-like articular. On the anterior internal side it is over- 

 lapped by a i)osterior prolongation of the splenial. (See Plate 9.) 



Articulai'. — The articular is a block-like bone higher than wide, 

 and, as in many reptiles, when in position was probably the most 

 posterior element of the mandible. In No. 1887, Yale University 

 Museum, as shoAvn by fig. 1, Plate 9, the articular has been crowded 

 up and forward from its normal position in the jaw. It could not be 

 determined whether there was an anterior prolongation of this bone 

 lying between the prearticular and supra-angular, as this region is 

 still enveloped in a hard sandstone matrix. 



Prcarticnlar. — In specimen No. 1887, Yale Museum, there was 

 found to be an extra element on the postero-internal side of the 



