80 
CiAccio^ on the Nerves of the Cornea. 
surface^ where they end in a very composite network or 
plexus. 
The number of the nerves of the cornea varies very much 
in different animals. This number can be determined with 
some certainty only in small animals^ because in the larger 
ones the cornea is so thick that in order to examine it with 
high powers_, it is necessary to make very thin sections^ in 
which we very often fail to find any nervous trunks, or not 
more than one or two. In small animals,, on the contrary, 
the cornea is thin enough to be examined microscopically, 
either entire, or only divided transversely into two parts. 
According to my observations, in the cornea of the sparrow 
there are thirty- one nerve- trunks ; in that of the mouse 
twenty-six, and in that of the frog about thirty. I say about 
thirty, because, in a sixth part of the cornea of this animal, 
I have seen nearly five trunks. Supposing, then, that in 
each of the remaining parts were the same number, the total 
sum will be as above. But this supposition is not quite cor- 
rect, for in the cornea the nerve-trunks are not at equal dis- 
tances from one another, so that in one part the number of 
the nerve-trunks may be greater than in another part. In 
the cornea of the frog, therefore, the nervous trunks may be 
more or less than thirty. 
Some observers have asserted that the nerves of the cornea 
in man are from twenty-four to thirty-six; but every one 
who considers the difference between twenty -four and thirty- 
six, will at once see that this is only a mere assertion, and 
nothing else. In man, as in other large animals, I believe 
it is very difficult to ascertain the precise number of the 
nerves of the cornea. I must say that, in calculating the 
nerve-trunks distributed to the cornea of the animals above 
mentioned, I have not taken the slightest notice of those very 
fine trunklets which, together with the large ones, enter the 
cornea at various depths. 
The corneal nerves also vary much in size. Not only is 
there a great difference in the size of the various trunks in 
the same animal, but between those of different animals 
when compared the one with the other. From my observa- 
tions, I am led to the conclusion that the nerves in the cornea 
of the mouse are larger than those in the cornea of the eel, 
frog, and sparrow. 
The manner in which the nerves of the cornea branch. 
It is generally admitted that the mode of distribution of 
nerves to the cornea is efiPected by dichotomous division. 
