BRAIN AND SPECIAL SENSE ORGANS 



The ceratopsian brain is known in at least five excellent instances, four of which are from the 

 skulls of Triceratops and one from Anchiceratops. Descriptions and figures have been published as 

 follows: 



N flaielUtus, No. 1821 Y.P.M., Ceratopsia Monograph, Fig. 31, p. 37, Fig. 33, p. 38 

 Triceratops serratus, No. 2416 U.S.N. M., Ceratopsia Monograph, Fig. 32, p. 37, Fig. 34, p. 39 

 Triceratops sp., No. 5740 U.S.N. M., Gflmore 1919 B, Fig^. 1; this Memoir, Fig. 31 

 Triceratops sidcatus, No. 4286 U.S.N.M., brain not figured 

 Anchiceratops omatus, No. 5259 A.M.N.H., Brown 1914, Pis. XXXIV, XXXV; this Memoir, PI. XI 



Hatcher says that the brain, compared with the size of the skull, is smaller in the Ceratopsia 

 than in any other known group of vertebrates. This is due in part to the great expansion of the skull 

 beyond the limits of the actual cranium, especially the crest and facial region. In proportion to the 

 cranium alone, the brain size compares favorably with that of other dinosaurs, and in actual size 

 considerably exceeds that of a stegosaur of equivalent body bulk. In S/egosaurus, there are marked 

 dilatations of the neural canal in the spinal column; a huge one in the sacrum, at least twenty times 

 the size of the cranial cavity, and a lesser one in the brachial region of the thorax. In Triceratops, 

 these dilatations, while present, are by no means so marked, for the tail, which was innervated largely 

 from the sacral nerve mass, is a much smaller organ relatively and had not the offensive and 

 defensive functions in the Ceratopsia which are usually attributed to that of S/egosaurus. 



From comparisons with studies by Dendy 1 on the mid-section of the skull and brain of Spheno- 

 don, Osborn 2 concludes that "The intracranial cavity in Tyrannosaurus corresponds with the outer 

 surface and foldings of the dura mater and is thus merely a cast of the outer envelope of the brain, 

 which gives us little idea either of the form or size of the brain itself. The reasonable inference is 

 that the intracranial cast of Tyrannosaurus greatly exceeds and possibly doubles in cubic capacity the 

 actual brain which was formerly contained within it. 



"In Sphenodon the cubic capacity of the dura mater envelope appears to be double that of the 

 brain itself. Thus the cast of Tyrannosaurus . . . gives us a means of measuring the size of the dura 

 mater envelope. It displaces 530 cubic centimeters of water. If the brain proper bore the same pro- 

 portion to the dura mater envelope as that of Sphenodon, the bulk of the brain of Tyrannosaurus 

 may be estimated at 250 cubic centimeters. The brain proper was extremely small in comparison 

 with the enormous size of the body." 



I find that the brain cast of Triceratops serratus displaces 300 cubic centimeters of water, which, 

 according to Osborn's conclusions, would give an estimated volume for the actual brain of not more 

 than 150 cubic centimeters. This, I imagine, would give much the same ratio of brain to body bulk 

 as in Tyrannosaurus. Triceratops and Tyrannosaurus were actual competitors in the same environ- 

 ment, so that their nervous and hence psychic requirements would be much the same, but far less 

 than those of a large ungulate and its competitive carnivore, today. 



The endocranial casts of both Tyrannosaurus and Triceratops, but more especially of Anchicera- 

 tops (PI. XI), show certain protrusions on the superior and lateral aspects which do not represent 

 cranial nerves but membranous extensions of the dura mater into corresponding depressions in the 

 endocranial wall. There is no evidence that the actual brain bore such appendages; they seem to 

 represent spaces for the passage of bloodvessels for cerebral nourishment. 



In the ceratopsian brain, the olfactory lobe is large, and the olfactory nerve emerges in the 

 young T. fabellatus skull from a single median foramen which, in the types of T . horridus and 

 prorsus, is divided into two by a median bony partition. But the skulls of horridus and prorsus are 



'Dendv, A., 1911. 



2 Osborn, H. F., 1912, p. 21. 





