1903.] Lull, Skull of Triceratops Serratus. 689 



length of the expanded posterior portion. There is no trace 

 of paired elements in the vomer. 



The palatines bound laterally the posterior part of the 

 narial fenestras, and are somewhat triangular in shape, with 

 the base of the triangle meeting the maxillaries in a squamous 

 articulation somewhat overlapping the dental foramina. 

 Posteriorly they are bounded by the pterygoids, and the 

 anterior portion runs upward over the jaw until it ends in a 

 large vacuity on the dorsal side. This vacuity is further 

 bounded anteriorly and externally by the maxillary, and 

 posteriorly by the pterygoid, and it lies above a point one 

 third of the distance from the posterior end of the dental 

 channel. 



The pterygoids are large and irregular with peculiar channels, 

 probably the eustachian canals, running obliquely from the 

 articulation with the posterior end of the maxillaries to the 

 median line; these channels are formed by thin, overarching 

 ridges of bone which in their mid-length almost meet. The 

 pterygoids form the posterolateral margins of the narial 

 fenestras in the rear of the palatine bones and embrace the 

 hinder end of the vomer. Anteriorly they are bounded by the 

 palatine and maxillary bones and possibly by the ectoptery- 

 goids, though the last -mentioned cannot be located in this 

 specimen ^ ; the ectopterygoids are not suturally separated 

 from the pterygoids themselves. Posteriorly the pterygoids are 

 met by the basisphenoid and in the median line they nearly 

 embrace the parasphenoid, or ' vomer ' of Broom. Laterally 

 they are broad and thin plate-like expansions which pass out- 

 ward and backward to meet opposing processes of the quad- 

 rate, though the precise limit of the pterygo-quadrate suture 

 is not everywhere distinct. 



The quadrates are well developed and firmly fixed in place 

 by the pterygoids within and the quadratojugals without. 

 They also pass backward and upward, forming, with the 

 quadratojugals, the lower boundary of the infratemporal 

 fossa. Posteriorly they join the squamosals, which are widely 

 expanded to form the lateral el ements of the frill. The 



» Marsh, O. C, Amer. Jour. Sci. (3). XLI, p. 171- 

 \Pecember, igoj.^ ^"^ 



