THE SPINAL C0LU5IN OF HEPTILES. 157 



destitute of mobility; and the heavy lumpish 

 movements of the animal, -without the slightest 

 elasticity or grace, are in keeping "with this 

 inflexibility of that portion of the spine. Tl\e 

 neck, however, is at liberty, and capable of 

 being protruded jor withdrawn and of being 

 bent in various directions, the ball-and-socket 

 articulations of the vertebra being very free. 

 The same observations apply to the vertebras of 

 tlie tail. 



Considered with regard to their skeleton, 

 the greater portion of which is, so to speak, 

 thrown outwardiv, tortoises are most extra- 

 ordinary creatures, and we know of no 

 vertebrated animals which resemble them. 

 Among mammalia, the armadilloes are covered 

 with a shield, and the manis with an armour of 

 thick scales; but in these cases, the plates and 

 scales are, like hairs or feathers, derived ex- 

 clusively from the integument, and have nothing 

 to do with the osseous frame-work. So, again, 

 among fishes, we see the ostracion, or box-fisli, 

 invested with an inflexible coat of mail, com- 

 posed of osseous plates united together, covering 

 the whole body, the tail and fins alone being 

 free. Yet the box -fishes cannot be compared 

 to the tortoises — for osseous as is their invest- 



