I903-] Lull, Skull of Triceratops Serratus. 687 



Palatal Aspect. 



The premaxillaries are only in part preserved. The max- 

 illaries are heavy bones uniting anteriorly in the median line, 

 in front of the narial fenestrae, by a pronounced dentate 

 suture. Anteriorly the premaxillaries overlap them above 

 and posteriorly they bifurcate, one limb, the dorso-lateral, run- 

 ning obliquely outward and backward to join the jugal, while 

 the postero-ventral limb unites posteriorly with the ptery- 

 goids. The maxillaries thus form the anterior and about two 

 thirds of the lateral walls of the large narial fenestras. In the 

 palatal face lies the alveolar channel, sculptured transversely 

 into a number of shallow grooves, incomplete sockets in which 

 the teeth were formed, forty in the right channel and forty -two 

 in the left. The dental channel, is 482.8 mm. in length with 

 an average width of 30 mm., which is somewhat less than its 

 original measurement, owing to crushing. Other measure- 

 ments may be found in the table on page 694. As in the 

 mandible, a row of dental foramina runs along the inner face of 

 the maxilla, one foramen being opposite each alveolar groove, 

 through which passed the blood-vessels needful for the rapid 

 forming of teeth in the dental magazine. The external face 

 of the bone also bears two such foramina. 



The vomer, or 'prevomer' as determined b}^ Broom,' is a 

 slender rod-like bone bridging fore and aft the space of the 

 narial fenestra. Anteriorly it is dilated into a flattened 

 rhombic expansion articulating by a squamous suture with 

 the united maxillary bones. Passing backward there appears 

 a median ventral keel giving the bone in its narrowest part, 

 about the middle, a triangular section. Further to the rear 

 the lateral edges bend downward to the level of the median 

 keel and then rise again to their f oniier level, where they give 

 rise to thin plate-like expansions which are embraced at their 

 posterior end by the pterygoid bones. Dorsally viewed the 

 vomer is seen to become trough-like, the depression being 

 about the width of the shaft of the bone and running the 



' Broom, R., Proc. Linn. Soc. \. S. W., 1902, pt. 4, pp. 545-560. 



