[lambe] PANOPLOSAURUS M I RUS 49 



upward to attain a moderate depth behind the predentary. In 

 front they narrow rapidly from above, with a sharp curve inward 

 beneath the predentary, to the symphysis. The outer surface of the 

 rami at their deepest part slopes considerably outward to the lower 

 border where it meets the lower horizontal surface at an angle of about 

 80 degrees. This sharp angulation ends suddenly near the hinder end of 

 the jaw, but lessens gradually to the front where it merges into the 

 horizontal inturn of the bone toward the symphysis. Posteriorly, a 

 rapid contraction in the depth of the rami is continued inward and 

 downward by a relatively slender projection or process providing the 

 cotylus for the articulation of the quadrate and made up largely, no 

 doubt, of the surangular, angular, and articular, although these ele- 

 ments have not been recognized separately in the type. 



Measurements of Mandible of Type. 



mm. 

 Length of mandible, in a straight line, from middle of an- 

 terior border of predentary to posterior end of ramus 310 



Length of ramus, approximately 280 



Greatest depth toward the back 72 



Greatest depth toward the front 50 



Distance across mandible inferiorly near hinder end of rami . 288 

 Distance from upper exterior border of ram.us, below cheek- 

 plate, in to alveolar border . 46 



Predentary. This element consists of an anterior median portion 

 and two relatively slender, backwardly directed, slightly divergent 

 lateral limbs which pass upward on the truncated anterior ends of the 

 dentaries with little diminution in their exterior depth. As seen from 

 above the outer contour is somewhat horseshoe-shaped, with the 

 curve flattened across the front and along the sides. The posterior 

 width (142 mm.) is considerably greater than the median length in 

 about the proportion of 3 to 2. 



The upper border of the bone throughout comes to a moderately 

 sharp edge and is fitted closely within the upper border of the mouth 

 opening (lower border of premaxillaries) . The anterior middle part 

 retreats rapidly backward beneath the mandibular symphysis, and ter- 

 minates posteriorly in a pair of short, liguiform processes one on 

 either side of the midline as in the Hadrosauridae. In Stegosaurus a 

 single median process is described by Gilmore as "being interposed 

 between the ends of the dentaries at the symphysis." The Hadro- 

 sauridae as a rule have three processes given off posteriorly from the 

 central portion of the predentary, an inferior median pair and a 



