R. S. Lull — Stegosaurus ungulatus Marsh. 371 



cartilage of special erecting muscles, and of great thickness of 

 tlie skin. 



There are isolated, highly rugose ossicles, doubtless of der- 

 mal origin, associated with the skeleton, which cannot be placed 

 with any degree of assurance, but which may have been scat- 



FiG. 8. 



Fig. 8. Section of the distal part of the tail. After Lull, s, caudal 

 spine ; other letters as in fig. 5. 



tered somewhat at random over the skin or concentrated at 

 especially vulnerable portions of the body. 



IV. The Central Nervous System. 



One of the most remarkable features of this unique reptile 

 lies in the form and proportions of the central nervous system 

 as shown by internal casts and measurements of certain regions 

 of tlie neural canal. 



The brain is remarkable for its extremely small size, the 

 entire cranial cavity, with a length of l-OS*^™ and a width of 

 30™', displacing but 56™ of water and having an estimated 

 total weight of but 2^ oz. The total weight of the animal must 

 have exceeded that of the greatest of living elephants, the 

 brain of wliich averages eight pounds or over fifty times the 

 weight of that of 8tegosatirus. 



In comparing the relative potential intelligence of the two, 

 one has also to bear in mind the great preponderance of the 

 cerebrum over the other parts in the elephantine brain, while 

 in Stegosaurus the cerebrum constitutes hardly more than a 

 third of the entire brain weight. The stegosanr 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 appar- 

 ently as well developed as may have been that of sight ; the 

 auditory sense I am not yet prepared to discuss. 



Passing backward along the neural canal, one finds two en- 

 largements _: one at the fore limbs, the bi-achial enlargement. 



