Figure 16. Ring of the Lemon-crested Cockatoo, which is like 

 the Macaws, very small. 



17. Ring of the Toucan, a hird not a third part the 



size of the preceding, but which has a much 

 larger ring. 



18. Ring of the Touraco or Plaintain Eater. 



19. Ring of the European Night Jar ; the bones are 



soft and the ring is very feeble. 



20. Ring of the Swift, proportionally one of the largest 



and strongest. 



PLATE 4. 



REPTILES. 



Figure 6. Sclerotic ring of the Iguana. 



6a. Two detached bones ; the outer edge of which 

 forms a kind of pedestal, contrary to what is 

 found in birds, where the outer edge is generally 

 the broadest ; in the present case the ring is 

 much strengthened from the extent to which the 

 bones overlap each other in consequence of this 

 peculiarity in their form. 



7. A front view of the ring of the Gecko, which in 



this surrounds the eye, as described by Cuvier, 

 and covers scarcely any part of the anterior por- 

 tion of the eye. 

 7a, A side view of the same ring. 



8. Ring of the Chameleon ; which covers the whole 



surface of the front of the eye except the pupil, 

 and shews the smallest aperture of any known 

 sclerotic ring. 



