Trof. 0. C. Marsh — Gigantic Ceratopmlce. 



195 



The brain-case is well ossified in front, and in old animals there 

 is a strong septum separating the olfactor}' lobes. 



Teeth of Tkiceratops. — The teeth of Triceratops and its near 

 allies are very remarkable in having two distinct roots. This is 

 true of both the upper and lower series. These roots are placed 

 transversely in the jaw, and there is a separate cavity, more or less 

 distinct, for each of them. One of these teeth from the upper jaw, 

 represented by figures of the natural size (Plate V. Figs. 3-6), are 

 typical of the group. 



The teeth form a single series only in each jaw. The upper and 

 lower teeth are similar, but the grinding face is reversed, being on 

 the inner side of the upper series, and on the outer side of the lower 

 series. The sculptured surface in each series is on the opposite side 

 from that in use. 



The teeth are not displaced vertically by their successors, but 

 from the side. The crown of the young tooth, also with two strong 

 roots, cuts its way between the alveolar margin and the adjacent 

 root of the old tooth, sometimes advancing between the two roots, 

 as might be expected. 



The teeth in this family are entirely confined to the maxillary 

 and dentary bones. The rostral bone, the premaxillaries, and the 

 pre-dentary, are entirely edentulous. 



Cervical and Dorsal Vertebra. — The atlas and axis of Tricera- 

 tops are coossified with each other, and at least one other vertebra 

 is firmly united with them (Woodcut, Fig. 1). These form a solid 

 mass, well adapted to support the enormous head. The cup for the 

 occipital condyle is nearly round, and very deep. The rib of the 

 second vertebra is coossified with it, but the third is usually free. 

 The centrum of the fourth vertebra is free, and the remaining 

 cervicals are of the same general form, all having their articular 

 faces nearly flat (Woodcut, Fig. 2). 



2. 1. 



Fig. 1. — Anterior cervical vertebrae of Triceratops porosus, Marsh ; side view. 



Fig. 2. — Fourth cervical vertebra of same series ; back view. 



a. anterior face of atlas ; d. diapophysis ; n. neural canal ; p. posterior face 

 of fourth vertebra ; r. rib ; s. neural spine of axis ; s' . neural spine of third 

 vertebra ; s" . neural spine of fourth vertebra ; z'. posterior zygapophysis. 



The anterior dorsal vertebrse have very short centra, with flat 

 articular ends, and resemble somewhat those of Stegosaurus, especially 

 in the neural arch (Woodcut, Figs. 3-4), 



