TRICEKATOPS HORRIDUS. 



121 



The anatomy of the occipital region may be well seen from behind, as shown in fig. 107. 

 The frill is for the most part wanting and the large hemispherical occipital condyle appears in 

 the center, which gives origin above to the elongated exoccipital processes, greatly expanded 

 distally and below to the short, stout basioccipital processes, while just in front of these may 

 be seen only the extremities of the basisphenoid processes resting against the broad plates of 

 the pterygoids, which diverge and give rise below to two processes, the broader and thinner 

 of which gives support to the quadrate from within, while the longer and more slender passes 

 downward and forward to meet the inferior branch of the maxillary. Above the occipital 



Fig. 107. — Posterior view of type of Tricemtops horridus, No. 1820, Yale Museum. Drawn under Professor Marsh's supervision, bo 

 Basioccipital; exo, exoccipital; fm, foramen magnum; pa, parietal; ply, pterygoid; qu, quadrate; so, supraoccipital; soli, supra- 

 orbital horn core; sq, squamosal. One-eighth natural size. 



condyle is the foramen magnum, situated entirely within the exoccipitals. Above this the 

 posterior surface of the exoccipitals shows two deep pockets or cavities situated one on either 

 side of a strong, vertical, median bar which expands somewhat just below the suture for the 

 supraoccipital. Laterally and superiorly the exoccipitals articulate with the squamosals. 



The supraorbital horn cores appear exceedingly massive. The rostral bone is also very 

 heavy and not so sharp along its infero-anterior border as in most other species where that 

 element is known. The nasal horn is very broad at the base and quite short and blunt. The 

 jugals, quadratojugals, and quadrates appear as usual. 



