18 



THE CERATOPSIA. 



Fig. 9.— Occipital region of type of Tri- 

 ceratops flabellatus, No. 1821, Yale Mu- 

 seum, seen obliquely from below. /, 

 Frontals; pf, postfrontals; as, alisphe- 

 noids; exo, exoccipitals; bo, basioccipi- 

 tals; bs, basisphenoids; spt, surface for 

 contact with pterygoids; ol, exit for 

 olfactory nerve; mec, median eustachian 

 canal. One-eighth natural size. 



lobe through a deep fossa, which doubtless lodged the pituitary body. They probably trans- 

 mitted the carotid arteries. One of these foramina is shown at ca in fig 8. Anteriorly the 

 basisphenoidal processes are received into deep pockets en the posterior surfaces of the thin 

 but widely expanded posterior wings of the pterygoids. 



The alisphenoids, including also the parasphenoids, with which they are so completely 



fused, even in young individuals, as to render the latter elements 

 indistinguishable, are extremely irregular in form. They are 

 firmly coossified with one another and with the exoccipitals and 

 the basisphenoid. Together with the latter element they usually 

 form the entire anterior portion of the brain case, save only the 

 extreme anterior portion of the superior border, which in some 

 instances is formed by the anterior projection of the united 

 postfrontals. Supero-posteriorly the alisphenoids articulate with 

 the supraoccipital and supero-anteriorty with the postfrontals. 

 Just beneath the lateral union of the supraoccipital and post- 

 frontals the alisphenoids are developed into a strong lamina or 

 buttress, which gives greater support to this region. Anteriorly 

 the coossified alisphenoids and basisphenoid are embraced bjr 

 the vomers and the posterior projections of the palatines, as is 

 well shown in fig. 24, from the type of Triceratops horridus, No. 

 1820 of the Yale Museum collections, though not so apparent 

 in the type of T. flabellatus, No. 1821 of the same museum, 

 in which these parts are less perfectly preserved. In the type 

 of T. flabellatus the olfactory nerves, as shown in fig. 9, leave the brain case by a single large 

 median foramen inclosed entirely by the alisphenoids, while in the type of T. horridus this 

 foramen is subdivided by a strong 

 but short median partition of bone, 

 as shown in fig. 27. As will be 

 shown later, however, this differ- 

 ence is probably due to age, and 

 is of no specific or generic im- 

 portance. In the latter species 

 the alisphenoids are continued for- 

 ward and form the entire roof of 

 the olfactory lobes, entirety ex- 

 cluding the postfrontals and giving 

 origin to that partition which has 

 just been mentioned as dividing 

 the foramen for the exit of the 

 olfactory nerves into two fora- 

 mina, conditions well shown in the 

 figure last cited. Near and an- 

 terior to the base of the ascending 

 lamina of the alisphenoid two 

 small foramina (ff f fig. 8), situated 

 one in advance of the other, pierce the bone and enter the brain cavity just back of the 

 olfactory lobe. At a distance of 38 millimeters behind the more posterior of these two 

 foramina is the anterior opening of the alisphenoid canal, or foramen rotundum. The alis- 

 phenoid canal is inclosed externally by a heavy bridge of bone, and is continued posteriorly for 

 35 millimeters, when it enters the foramen ovale. The latter foramen is large and is sepa- 

 rated from the foramen lacerum posterius by a strong bonj^ partition, which is pierced by a 

 small foramen that may possibly represent the external auditory opening. Just beneath the 



Fig. 10.— Skull of type of Triceratops flabellatus, No. 1821, Yale Museum, seen from left 

 side, h, Supraorbital horn core; c, supratemporal fontanelle; b, orbit; e, epoccipi- 

 tal; q, quadrate and quadratojugal; a, anterior nares; h' t nasal horn core; r, ros- 

 tral; p, predentary. One-twelfth natural size. After Marsh. 



