694 Bulletin American Museiwi of Natural History. [Vol. XIX, 



seems to have been brought about by the mechanical necessity 

 of a base widened transversely to meet a lateral strain in the 

 shearing process of mastication and the subsequent constric- 

 tion of this base into an inner and outer pillar due to the 

 crowding of the crowns of adjacent teeth set at a lower level. 

 There could have been no lateral movement in mastication, 

 but a chopping motion, possibly with a slight orthal movement 

 combined with it. The food gathered by the cutting beak 

 was probably chopped into short pieces by the teeth, being 

 kept in the mouth by the muscular wall of the cheeks. It is 

 doubtful whether the gape of the mouth had a posterior extent 

 further than the anterior end of the tooth series, as otherwise 

 the portions of food chopped off, falling outside of the lower 

 teeth, could not have been retained in the mouth. 



The alveolar grooves are equally developed in the inner 

 surface of both inner and outer walls of the dental channel 

 and not in the inner surface of the outer wall only as in 

 Trachodon {Hadrosaurus) as shown by Lambe.^ This is due 

 to the fact that in Triceratops the crowns of the teeth do not 

 form so flat a tassellated pavement when viewed from within; 

 their position in the jaw being more nearly vertical than in 

 Trachodon. 



Measurements. 



Length of skull (estimated) 2160 mm. 



Width across frill 1578 



Maxillary bones, length 672 



" " length of dental channel 482.8 



" " average width dental channel 30 



Premaxillary bones, width at posterior end 177 



Vomer, length 410 



" width at anterior end 70 



" width of shaft 15 



Palatine bones, length 293 



Occipital condyle, diameter 115 



Foramen magnum, width 47 



" " height 39 



Basioccipital bone, width 280 



Exoccipitals, distance from tip to tip 790 



* Lambe, L. M., 1903, Ottawa Naturalist, Vol. XVII, pp. 136, 157; Osborn. H. F., 

 and Lambe, L. M., 1902, Contributions to Canadian Paleontology, III, Part II, p. 73. 



