Lull — Ftinctio7is of the ^'Sacral Brain " in Dinosaurs. 473 



bears for a vegetative diet, and the tremendous growth 

 of certain plants such as the water hyacinth in the Nile 

 or the waters of New Zealand seems to offer an analogy 

 to what might well have been true of certain aquatic 

 vegetation of the Mesozoic upon which these creatures 

 fed. The teeth were now solely prehensile, sufficiently 

 so for their owners' purpose, but less efficient than those 

 of the Theropoda. The food was in no sense masticated 

 and the inference that a powerful muscular gizzard-like 

 stomach was developed is irresistible, for which the pres- 

 ence of stomach stones, gastroliths, within the ribs of 

 more than one specimen may be taken as added argument, 



Predentates. — The predentate dinosaurs, on the other 

 hand, had a differentiated mouth armament. The ante- 

 rior or prehensile portion was toothless, except in Hyp- 

 silophodon, but was sheathed with a horny, turtle-like, 

 cropping beak of varying form. The posterior portion 

 of the jaws bore the actual dental battery, consisting of 

 a series of successional teeth which also varied in effici- 

 ency and degree of development in accordance with their 

 owners' food, as do those of the ungulate mammals. 

 The Jurassic and early Comanchian forms, such as 

 Camptosaurus and Laosaurus, were analogous to the 

 browsing ungulates whose brachiodont teeth are fitted 

 to succulent herbage, while the later trachodonts had a 

 dental battery fully as efficient as that of a horse. These 

 dinosaurs chopped their food into short lengths before 

 swallowing, and it may be that the term mastication, 

 which, however, implies a grinding or crushing rather 

 than chopping, may be properly applied to them. Their 

 need of a gizzard-like organ would seem to be less great 

 than in the sauropods. 



8tegosaurus, on the other hand, possessed a very 

 imperfect dental battery, as the teeth were both small 

 and relatively few in number — ^very inadequate appar- 

 ently for their owner's needs. This genus, however, 

 exhibits a number of characters which, in the Sauropoda, 

 have been taken as indicating an aquatic or at least 

 amphibious life. They are, first, the solid, massive char- 

 acter of the limb bones and the imperfection of their 

 articular ends, those of the stegosaur showing a rugosity 

 fully proportional to those of Brontosaurus. The high 

 position^ of the ribs, bringing the lungs well toward the 

 dorsal side of the body, and the strongly compressed tail 



Am. Jour. Sci.— Fourth Series, Vol. XLIV, No. 264.— December, 1917. 

 33 



