28 



THE CEKATOPSIA. 



tudinal portions of the palatines meet, they are produced into long, pointed processes which fit 

 nicely into notches on the supero-internal surfaces of the maxillaries, as is well shown in fig. 20. 



Fig. 24.— Portion of central region of skull of Triceratops horridus (type), No. 1820, Yale Museum, as seen from right side with external wall 

 removed, showing relations of the various internal bones of the cranial region to one another, h, Supraorbital horn core; pf, postfrontal; 

 x, cavities in postfrontal; of, olfactory foramen; al, alisphenoid; o, optic foramen; fo, foramen ovale; earn, external auditory meatus; 

 ftp, foramen lacerum posterius; bs, basisphenoid; pt, pterygoid; pi, palatine; tr, transverse; q, quadrate; qj, quadratojugal surface; as, 

 articular surface for lower jaw; mx, m, maxillary; v, vomer; n, nasal; no, nasal opening; nh, nasal horn; pmx, premaxillary; r, rostral. 

 One-twelfth natural size. 



Just above this process the anterior border of the palatine incloses posteriorly an elongated oval 



foramen, which is bounded anteriorly by the ascending branch of the maxillary. This foramen 



passes from the cavity of the mouth to the infratemporal cavity 



and may be called the maxillopalatine foramen. It is situated, 



as shown at v, fig. 20, just below the much smaller infraorbital 



foramen, from which it is separated by a slender process of the 



maxillary. Above, the palatines approach each other and embrace 



between them the vomers, the superior extremity of the pterygoids, 



and the median blade of the alisphenoids. The articulation of 



these various elements with one another is well shown in the 



accompanying figures. 



THE VOMER. 



Only the posterior portion of the vomer is shown in any of 

 the skulls at my disposal, though it is possible that it may be 

 complete in some of the skulls not yet fully prepared. 



The vomer is present in a skull, No. 970, of the collections 

 of the American Museum of Natural History, and has been 

 described as follows by Dr. R. S. Lull:" 



The vomer or "prevomer" as determined by 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. Farther to 

 the rear the lateral edges bend downward to the level of the median keel and then rise again to their former level, where 



Fig. 25.— Palatine region of type of Tri- 

 ceratops horridus, No. 1820, Yale Mu- 

 seum, with anterior portion of skull 

 removed, seen obliquely from below 

 and in front, v, Vomer; tp, trans- 

 verse process of palatine; ipf, in- 

 terpterygoid foramen; pi, palatine; 

 pt, pterygoid; pp, pterygo-palatine 

 foramen; mx, maxillary. One-eighth 

 natural size. 



<■ See " Skull of Triceratops serratus," Bull. Am. Mus. Nat. Hist., vol. 19, pp. 685-695. 



