DINOSAURS. 113 



easily imagine that a single deadly blow from such a tail would 

 be sufficient to drive away, if not to kill, one of the carnivorous 

 enemies of the species. All the plates and spines were, during 

 life, protected by a thick horny covering, which must have in- 

 creased their size and weight. Such a covering seems to be clearly 

 indicated by certain grooves and impressions that mark their sur- 

 faces. (See Fig. 28.) The largest plates are unsymmetrical, 

 and were probably arranged along the back, as in our restoration, 

 Plate IX. It will be noticed, by those who are familiar with our 

 first edition that Plate X. gives a somewhat different representa- 



I 2 



FIG. 26. Tail vertebras of Stegosaurns. (After Marsh.) 

 I. Side view. 2. Front view. 



tion of the Stegosaur, in which the length of the hind limbs is 

 more apparent, and also they are more free from the body. 



Finally, the Stegosaur displays a rather remarkable feature ; 

 for a very large chamber was found in the sacrum 1 formed by 

 an enlargement of the spinal cord. The chamber strongly 

 resembled the brain-case in the skull, but was about ten times 



1 The sacrum may be thus defined : the Vertebras (usually fused together) 

 which unite with the haunch-bones (ilia) to form the pelvis. 



I 



