VOL, XVII.] " ?HILOSOPHICAL TRANSACTIONS. 633 ' 



can see it have not these nerves, and the pair of nerves belonging to the upper 

 bill is considerably smaller, in proportion to the fowls, than those observed 

 above ; whence it is probable that these nerves were designed for some great use, 

 both on the account of their number and their size ; and that the use to be 

 assigned to them must be to enable them to distinguish, whether by tasting or 

 feeling, I will not now distinguish, their food, there being a necessity of a more 

 exquisite sense in these fowls than in any other. Fig. 15 represents those in a 

 duck's head, where a a denote the edge of the cranium, which was in part 

 removed for the clearer view of these nerves; bb are the cells about the ear, 

 between the two tables above described ; c c the brain laid bare with its blood 

 vessels ; ddd the three nerves on one side, e the optic nerve ; fff the skin and 

 part of the bone, removed to bring the nerve in view ; g g the two nerves 

 expanded near the end of the upper bill ; hh that in the lower. 



All the eyes of fowl and of fish, that I have examined, were more or less 

 cartilaginous ; for the sclerotis is a cartilago sui generis, especially near the 

 cornea, in all these animals. And in the larger sorts of both, I remembered 

 to have found the whole sclerotis such a kind of a cartilage. 



In the eyes offish, I observed that the processus ciliaris is not fastened to the 

 joining of the cornea et sclerotis, as in all other animals that I have dissected, 

 so as to hinder the watery humour from going any further backward. For I 

 constantly observed that the humor aqueus may move a good way backward in 

 some, and in others almost as far as the optic nerve. 



I have, in as many fish as I could conveniently examine carefully, found a 

 membrane, which covered the tunica cornea, so as not to let any water come 

 to it. This answers the membrane nictitans in fowl, and reaches on all sides 

 to the cutis of the fish to which it is fastened ; this is transparent, and pretty 

 thin, and so is also the cornea, if compared to that of the quadrupeds. 



I have frequently observed in smaller fowl, that the membrane of the drum 

 was double ; for by gently pulling away the membrane lining the tube of the 

 ear, I observed at the bottom of it a transparent membrane, which at first I 

 took to be the membrane of the drum, but on examination I found that this 

 membrane was still entire, and in its proper place. I have sometimes observed 

 this in larger fowl, in a seal, and in some other animals, and am apt to think 

 from a case mentioned in Du Verney's book of the ear, that it is so in men ; 

 and if so, it is likely it may be so in most, if not in all animals. The observa- 

 tion was as follows : a person that was deaf for some time died, whose ears Mr. 

 Du Verney examined, in order to find out the cause of his deafness, which he ' 

 found to be a thick membrane growing in the ear before the drum, which hin- 

 dered the impulses in the air to be communicated to it. Now I take it to be 



