2Q 



THE CEKATOPSIA. 



shown in fig. 21, is also in contact with the inferior process of the palatine for a short distance 

 along its upper and inner margin. The external surface of the maxillary is perforated by a 

 number of smaller and larger foramina, placed rather irregularly; and on the internal side, about 



2 inches above the alveolar bor- 

 der, there is a series of small 

 foramina extending throughout 

 the entire length of the dental 

 series. These doubtless served 

 for the transmission of nutrient 

 blood vessels to the teeth." 



The general form and appear- 

 ance of the maxillary when de- 

 tached from the surrounding ele- 

 ments is well shown in fig. 22, 

 drawn from the type of Triceratops 

 flabellatus. In this specimen only 

 a few teeth protrude from the 

 alveolar groove, and in this respect 

 the drawing gives a very imper- 

 fect idea as to the appearance of 

 the dentition when complete and 

 in position. The position of the 

 infraorbital foramen differs from 

 that in the type of T. serratus, where it is located between the superior border of the maxillary 

 and the inferior margin of the nasal. 



Fig. 20. — Internal view of maxillary, palatine, and lachrymal, with pterygoid and quad- 

 rate drawn in in outline. From type of Triceratops flabellatus, No. 1821, Yale Museum. 

 I, Lachrymal; if, infraorbital foramen: v, vacuity between temporal fossa and mouth; 

 mx, maxillary; pi, palatine; x, foramen between pterygoid and palatine: pt, ptery- 

 goid; a, surface for contact with basisphenoid process; q, quadrate; df, dental 

 foramina; ab, alveolar border. One-eighth natural size. 



THE TRANSVERSE BONES. 



The transverse bones, or ectoptery- 

 goids, are reduced to little more than 

 flattened ossicles on the superior and 

 external surface of the posterior and 

 inferior process of the maxillary, as 

 shown at tr in figs. 21 and 24. Above 

 they are in contact with the palatines 

 and below, on the inner side, with the 

 pterygoids. They are very rudimen- 

 tary, have no contact with the jugals, 

 and serve almost none of the purposes 

 of these elements as represented in the 

 skulls of most recent reptiles. 



THE PTERYGOIDS. 



Fig. 21. — External view of right maxillary, palatine, pterygoid, and transverse 

 bones, with jugal drawn in in outline. From type of Triceratops flabella- 

 tus, No. 1821, Yale Museum, o, Orbit; I, lachrymal; pi, palatine; if, infra- 

 orbital foramen; ma:, maxillary; tr, transverse; x, foramen between pala- 

 tine and pterygoid; pt, pterygoid; j, jugal; sq, surface for quadrate; 06, 

 alveolar border. One-eighth natural size. 



The pterygoids are very irregular in 

 form, as shown in fig. 23. Inferiorly and 

 posteriorly they are broad and thin, the posterior portion being expanded so as to form a broad 

 wing, convex externally and concave internally. The anteroinferior angle of this portion is thick 

 and is lodged in a deep notch on the internal side of the quadrate, while above and posteriorly the 



a While this view of the function of these foramina is the prevalent one, Doctor Rose has advanced another theory which carries great 

 weight. He believes that the foramina were for the infolding of the mucous membrane from which the tooth papillae were formed and which 

 could no longer fold in in the ordinary manner because of the great depth of the dental chamber which contains the magazine of teeth. The 

 nerves and blood vessels were within the jaw in their normal position and the use of the foramina for their transmission from the outside 

 would imply the development of an entirely new set of nerves and blood vessels. He also holds that the foramina are much larger than they 

 would be if they were nutrient only. (See F. B. Loomis,Palaeontographica, Bd. 46, 1900, p. 250.)— R. S. L. 



