474: Lull — Functions of the ^^ Sacral Brain''^ in Dinosaurs. 



with its high neural spines and well developed chevrons 

 are also suggestive. Add to these a mouth armament no 

 more effective than that of a sauropod, and the associa- 

 tion of their remains in a common burial, and the infer- 

 ence of sunilarity of habitus and food is perhaps justi- 

 fied. Just w^hat effect the tall upstanding armor plates 

 would have upon the navigable powers of Stegosaurus is 

 not so clear, but they may have incommoded him under 

 such conditions no more than on land. 



It may be fairly assumed, therefore, in view of the wide 

 apparent range of feeding habits on the part of dinosaurs, 

 and their relationship to the crocodiles on the one hand 

 and to the birds on the other, that their digestive system 

 was closely comparable both in the development of its 

 parts and in its innervation to that of these living forms. 

 With the birds, the degree of development of the gizzard 

 varies directly with the consistency of the food. Grami- 

 nivorous birds possess the strongest muscular layer and 

 the thickest horny lining, while in the series from the 

 insectivorous birds to the birds of prey this condition 

 becomes gradually less marked and the division of labor 

 between the glandular proventriculus and the mechanical 

 gizzard less noticeable (Newton). The assumption of a 

 similar gradation in the development of this organ in the 

 dinosaurs seems also warranted. 



Innervation of the alimentary canal. 



In the reptiles such as the python, crocodile, or turtle, 

 the vagus nerve (Xth cranial) is the principal transmit- 

 ter of stimuli which initiate digestive activity, certain of 

 its fibers being distributed to the muscles and mucous 

 membrane of the fauces, the oesophagus, and the stomach, 

 and it finally terminates at the beginning of the intestine 

 at the pancreas. 



Cranial casts of Tyrannosaurus^ and of Stegosaurus 

 and Morosaurus, representing, therefore, the three main 

 dinosaurian groups, all show exits for the IXth to Xlth 

 cranial nerves, thus including the vagus, relatively larger 

 if anything than in the crocodile. It is fair to assume, 

 therefore, that this nerve was at least as weU developed 

 in the dinosaurs and that its distribution and function 

 were comparable. 



" H. F. Osborn, Crania of Tyrannosaurus and Allosaurus, Mem. Amer. 

 Mus. Nat. Hist., new series, vol. i, pt. 1, 1912, pp. 1-30. 



