126 EXTINCT MONSTERS 
birds are descended from Dinosaurian ancestors; while others, 
with Professor Owen, consider the resemblance accidental, and in 
no way implying relationship. Huxley has proposed the name 
Ornithoscelida, or bird-legged, for these remarkable reptiles. 
Dinosaurs must have formerly inhabited a large part of the 
primeval world; for their remains are found, not only in Europe, 
but in Africa, India, North and South America, and even in 
Australia; and the geologist finds that they reigned supreme on 
the earth throughout the whole of the great Mesozoic era, Their 
bodies were, in some cases, defended by a formidable coat of 
armour, consisting of bony plates and spines, as illustrated by 
the case of Polacanthus (p. 173), thus giving them a decidedly 
dragon-like appearance. The vertebra, or bony segments of the 
back-bone, generally have their centra hollow on both ends, as 
in the Ichthyosaurus; but in the neck and tail they are not 
unfrequently hollow on one side and convex on the other. In 
some of the largest forms the vertebre are excavated into hollow 
chambers. This is apparently for the sake of lightness; for a 
very large animal with heavy solid bones would find it difficult 
to move freely. In this way strength was combined with 
lightness. 
All the Dinosaurs had four limbs, and in many cases the hind 
pair were very large compared to the fore limbs. They varied 
enormously in size, as well as in appearance. Thus certain of 
the smaller families were only two feet long and lightly built; 
while others were truly colossal in size, far out-rivalling our 
modern rhinoceroses and elephants. 
The limbs of Cetiosaurus, for example, or of Stegosaurus, 
remind us strikingly of those of elephants. The celebrated Von 
Meyer was so struck with this likeness that he proposed the name 
Pachypoda for them, which means thick-footed. Professor Owen 
