BRAIN AND SPECIAL SENSE ORGANS 73 



in the form ol B Cochlea must have been present for the perception of sound, luit it would not have 

 had the degree of development seen in the birds and mammals. Reverting to the semi-circular 



canals once more, it is interesting to note that the plane of the horizontal one with reference to the 

 longitudinal axis of the skull has been considered as evidence for the static carriage of the head with 

 muzzle pointed somewhat downward near the ground, a position which we had previously deter- 

 mined as correct upon evidence afforded by the occipital condyle and the fused anterior ccrvicals, the 

 long axes of which should he in line. The comparatively large extent of the circular or angular 

 sweep of the vertical canals, as opposed to those of the horizontal ones, has been taken as an index 

 of the extent of accelerated movement habitually carried out by the animal in the plane and in the 

 directed sense of the canal itself. The conclusion is, therefore, "that Anchiceratops vigorously swung 

 its head about a vertical axis to a far less extent than about horizontal axes." 4 But A>i, hii rratops, 

 with well developed vascular impressions on the underside of the crest, must have had the latter 

 largely free of the neck musculature and the head was, therefore, capable of freer rotational move- 

 ment than Cetitrosaurus, for instance, which we necessarily restored with the crest, except for the 

 periphery, in contact with the underlying muscles (PI. II, B). In Centrosaurus, freedom of 

 rotational movement seems to have been very limited. 



Another interesting detail of the nervous system which has been alluded to previously is 

 the lack of bony protection for the spinal cord from its exit from the foramen magnum to its 

 entrance into the enclosed neural canal of the axis, a distance, according to Tait and Brown, of at 

 least 1 1 inches in a large Triceratops. Moreover, the plane of the occiput slopes away from that of 

 the beginning of the neural arch, the one sloping from below upward and backward, the other, 

 upward and forward, so that the upper surface of the spinal cord was free of bone restriction to a 

 greater extent than the lower. All this is taken by Tait and Brown as further evidence for marked 

 rotational movement of the skull on its longitudinal axis, necessitated by the laterally compressed 

 form of the prehensile beak and its use in severing vertically growing stalks of vegetation such as tall 

 ferns, cycads, Equisetae, and other elevated and luxuriantly crowned plants which formed the creature's 

 food. But the Ceratopsia lived during a time of modernized flora and it is not necessary to imagine 

 their dietary restriction to plants of so primitive a character. Frankly, I do not believe that the head 

 was ever rotated to such an extent that "like a hen viewing a hawk, they looked upwards with the 

 upper eye" r ' and thus were enabled to grasp with their recurved beak the bases of vertically growing 

 stems and bring the foliage down from above. 



Hatcher," in speaking of the sense organs of the Ceratopsia, says that the large comparative 

 size of the olfactory lobe and the foramina for the exit of the olfactory nerves, as well as that of 

 the orbits, and the ample dimensions of the optic foramina, imply that both the sense of smell and 

 that of sight were well developed. He thought, however, that from the structure of the skull in the 

 auditory region and the small size of the foramen through which the auditory nerve may have had 

 its exit the sense of hearing was extremely dull. And, as he says, perhaps this deficiency in hearing 

 may have hastened to some extent at least the extinction of the group. In the Anchkeratofs brain 

 case, while the cochlea could not be explored, there is, nevertheless, little evidence of deficiency of 

 the auditory apparatus, nor am I inclined to accept Hatcher's conclusion in the matter, especially his 

 final suggestion that this difficulty may have hastened extinction. Triceratops and Torosourm lived 

 to the very close of the Mesozoic, when the wholesale reptilian extinctions occurred. It is not neces- 

 sary to find any specific cause of racial death which would apply to Ceratopsia alone, for that death 

 was indiscriminate among reptiles and not restricted solely to the ceratopsians. 



Even though the sense of hearing was somewhat dull as compared with that of modern graz- 

 ing mammals, I imagine the noise of approaching danger was proportionately loud; for there were 

 no stealthy beasts of prey of sufficient prowess to menace a Triceratops in his prime. 



4 Tait, J., .in J Broun, B., 1928, pp. 2 1 , 22. 



r 'Op. cit., p. 23. 



1 Hatcher, M.rsh, Lull, 1907, pp. 38-39. 



