HISTORY OF THE PERISSODACTYLA 311 



of bony protuberances from the front of the skull and, from 

 their shape, could hardly have been sheathed in horn. The 

 long, immensely broad and massive head resembled that of 

 some fantastic rhinoceros, as did also the body and limbs. 

 The brain was quite absurdly small, the cavity for it, lost in 

 the huge skull, would hardly contain the fist of an ordinary 

 man ; these great beasts must have been incredibly dull and 

 stupid, surpassing even the modern rhinoceroses in this respect. 

 As is generally true in mammals which have horns, antlers, 



Fig. 162. — Skull of t Titanotherium datum. American Museum. 



or similar weapons borne upon the skull, or very large tusks, 

 the bones of the brain-case were made enormously thick and 

 yet lightened by an intricate system of communicating cavities 

 or "sinuses," separated by many bony braces and supports 

 connecting the inner and outer denser layers, which form the 

 surfaces of the bones. In this way the skull is made strong 

 enough without any proportionate increase of weight to endure 

 the severe shock of impact, when the horns or tusks are made 

 use of. The principle is the same as the engineer employs 

 in designing a steel truss-bridge. The upper profile of the head 

 was deeply concave, just as it is in those rhinoceroses which 

 are armed with nasal horns. 



