44 



UNITED STATES NATIONAL MUSEUM. 



cerebrum constitutes hardly more than a third of the entire brain weight. The iStesrosour brain has a 

 very large olfactory portion, small cerebellum, large medulla, and a hypophysis which is remarkable 

 not only for its size, but also for the peculiar shape. The sense of smell was apparently as well devel- 

 oped as may have been that of sight; the auditory sense I am not yet prepared to discuss. 



Fio. 11. — Tooth of Sterosaukus ungui..\tu.s Maesh. a, N.vtueal size; h, c, d, 

 twice natuea-i. size: 6, outer view; c, end view; d, top view. all after 

 Marsh. 



The teeth in Stegosaurus ^ are confined exclusively to the maxillary and dentary 

 bones. They are not differentiated, the form and sculpturing remaining the same 

 throughout the series. Each tooth consists of a laterally compressed, vertically 

 striated crown having denticulate margins, and a long, cylindrical fang. The 

 outer face of the crown is shghtly convex vertically, while the inner face is slightly 

 concave. There is a rounded cingulum at the base of the crown, this being more 

 pronounced on the exterior face (fig. 11). The denticles in cross section are rounded 

 with a blunt point. The number of denticles on the teeth of Stegosaurus stenops 

 is variable. I have found teeth with as few as four and others with as many as 



seven on each side of 

 " -' the apical denticle. The 



apical denticle is always 

 on the median vertical 

 line, not posterior to it 

 as in the teeth of AnJcy- 

 losaurus ~ or Troodon. 



The teeth are held in 

 distinct sockets. Those 

 worn out or lost through 

 accident are replaced by 

 germ teeth developed in cavities within the jaw. Specimen No. 4934 shows 

 quite clearly the relationship of the germ and functional teeth (fig. 12). The 

 crown of the germ tooth lies on the inside of the base of the functional tooth, 

 the crown resting against the root of the old one, and, as usual among the 

 dinosaurs, ascends or descends according to whether they are in the upper or 

 lower series. It appears that there are not more than two teeth in a vertical 

 series. The teeth of the functional rows present a very regular cutting edge, as 

 contrasted with the irregular series in CamptoSaurus and Triceratops. Many of 

 the crowns in this series (No. 4934) show marks of wear, being obliquely ground. 

 Twenty-two teeth can be coimted in the right maxiUary of No. 4934 and the 

 complete m axillary series may have consisted of two or three more. In the dentary 

 of specimen No. 4935 there are aveoli for 23 teeth. With the germ teeth, there 

 were 46 in each jaw or 184 functional teeth in the complete series of the skuU. 

 The small weak structure of the teeth is most remarkable when the great size of 

 the animal is taken into consideration. The oblique wear of the teeth would 

 indicate that the bite was shear-like, as in the other predentate dinosaurs. The 

 teeth are invisible from the outside when the jaws are closed. Their weak structure 

 would imply, as LuU^ has pointed out, a "food of yielding character which did 



> Marsh in Amer. Jouni. Sci., vol. 19, 1880, p. 255, pi. 6, figs. 4 and 5, describes and figures teeth that afterwards were lound to 

 pertain to the Sauropod genus Diplodocus. 



2 Bamum Brown, Bull. Amer. Mus. Nat. History, vol. 24, 190S, p. 191, figs. 5 and 8. 



3 Amer. Joum. Sci., vol. 30, 1910, p. 3fi7. 



