172 0. C. Marsh — The gigantic Ceratopsidw, 



The Brain. 



The brain of Triceratops appears to have been smaller in 

 proportion to the entire skull, than in any known vertebrate. 



The position of the brain in the skull does not correspond 

 to the axis of the latter, the front being elevated at an angle of 

 about thirty degrees (Plate II, figure 7). 



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

 there is a strong septum separating the olfactory lobes. 



Teeth of Triceratops. 



The teeth of Triceratops and its near allies are very remark- 

 able 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 r 

 represented by enlarged figures (Plate II, figures 8-11), and 

 another tooth here exhibited, 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, sometimesad van cing 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 premax- 

 illaries, and the pre-dentary, are entirely edentulous. 



Cervical and Dorsal Vertebra. 



The atlas and axis of Triceratops are coossified with each 

 other, and at least one other vertebra is firmly united with 

 them. These form a solid mass, well adapted to support the 

 enormous head (Plate III, figure 1). The cup for the occipital 

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

 vertebra is coosified 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 (Plate III, figure 2). 



The anterior dorsal vertebrae have very short centra, with 

 flat articular ends, and resemble somewhat those of Stegosaurus, 

 especially in the neural arch (Plate III, figures 3-4). 



The posterior trunk vertebrae have also short, flat centra, 

 but the diapophyses have faces for both the head and tubercle 



