8 



in the Iguana, these bones (from which the figure in Dr. Buck- 

 land's Bridge water treatise was taken) are remarkably broad at 

 their inner edge, and overlap each other to a greater extent than 

 I have observed in any birds, thereby greatly increasing the 

 strength of the convex ring ; the external edge forms a kind of 

 pedestal or foot; in birds the external edge is generally the 

 broadest. The Chameleon has the bones of the same form as 

 the Iguana, but the pedestal is less produced ; the ring is very 

 strong; and to increase still further the strength of the eye's 

 defence, the bones are covered with the external skin of the 

 animal, leaving only the pupil exposed. The Gecko has the 

 ring of very slight texture, and it merely surrounds the lateral 

 part of the eye, as described by Cuvier ; the single bones (of 

 which I have only preserved one specimen) are very slight, and 

 from back to front exhibit a considerable curve. In fossil 

 Saurians, these bones are of a very different and less complex 

 form than those of the Iguana or Chameleon ; they appear to be 

 merely oblong bones of uniform shape, forming a protection to 

 the front of the eye ; they are beautifully figured as placed in 

 the head of the Ichthyosaurus in Dr. Buckland's treatise ; and 

 I have here, from our Geological collection, as beautiful an 

 example of these bones in situ. 



Note. The Paper was illustrated by anatomical preparations of the sclerotic 

 rings. Figures of many examples may be seen in the plates which accompany this 

 volume. 



