DINOSAURS. 
IT3 
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- 
Fig. 26. — Tail vertebrae of Stegosaurus. (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 ^ formed by 
an enlargement of the spinal cord. The chamber strongly 
resembled the brain-case in the skull, but was about ten times 
^ The sacrum may be thus defined : the Vertebra (usually fused together) 
which unite with the haunch-bones {ilia) to form the pelvis. 
I 
