R. /S. Lull — Cranial Musculature in Dinosaurs. 393 



In the chameleon the casque generally contains five bony 

 elements : a median interparietal, two lateral squamosals, and, 

 connecting these in the rear, a pair of slender parietal bars 

 (fig. 2). These structures enclose two lateral supratemporal 

 fossae generally of large extent, though in some species, as 

 Chameleo jpumilis (fig. 3), much reduced owing to the great 

 development of the parietal elements of the crest. (Parker 

 1881, p. 97.) In the Triceratops the crest contains the same 

 elements except that the parietal region is composed of but one 

 bone, no trace of sutures having been found as yet. Here the 

 supratemporal fossae are relatively small and do not lead 

 directly through the crest or frill but downward and forward 



Fig. 4. Torosaurus latys; skull, top view. 



beneath the postfrontal bones and above the exoccipitals and 

 jugals into the spacious cavities within the false roof of the 

 skull (vide infra, p. 395), fig. 6. 



In the Judith River genera, Ceratops, Monoclonius, and 

 Centrosaurus, and in Torosaurus of the Ceratops beds, the 

 crest is perforated by a pair of relatively immense parietal 

 fenestras, absent in Triceratops and its near relative Dicera- 

 tops. These fenestras seem at first sight to be the equivalents 

 of the supratemporal fossae of the chameleon, as their relation- 

 ship with the bony elements of the frill is practically the same. 

 This I believe to be partially true : the fenestras in the Cera- 



