NUNNELEY; ON THE CRYSTALLINE LENS. 141 
The axis of the lens is a line drawn from the centre of its 
anterior surface to that of its posterior. This in the human 
adult measures from the *18 to ‘22 of aninch. The diameter 
is a line drawn across from one point of the margin to the 
opposite, so as to divide the junction of the two surfaces. It 
measures from *31] to ‘36 of an inch in every direction, so 
that the lens is circular in its outline. This it is commonly 
regarded as being, not only in man, but in all animals. I am 
not, however, quite certain that some, which have the 
pupillary aperture very much extended horizontally, have 
not the lens also slightly broader in the horizontal than in 
the vertical direction. I have thought the measurements in 
some instances have been so. The axis of the lens is supposed 
to eorrespond exactly with the centre of the pupil. Now, as 
this is in most persons somewhat, and in some considerably, 
inclined towards the nasal side of the eye, were it so the axis 
of the lens would not correspond with that of the eyeball, 
but lie to its inner side. It is, however, far more probable 
that the axes of the lens and of the eyeball exactly cor- 
respond. 
The lens consists of its proper structure and its containing 
capsule. These are of totally dissimilar tissues. 
It is curious to note the very exaggerated notions which 
formerly were entertained as to the great density of the crystal- 
ine lens. Thus Matrejean concluded, from some experiments 
he made, that it is heavier than sulphuric acid or aqua 
fortis. But Dr. Porterfield informs us that Dr. Robertson 
weighed five crystalline lumens of the oxen’s eye and three 
of the sheep’s, and found the mean of the oxen 1°1134, of the 
sheep 1:1033, and of the eight to be 1:1083, from which he 
presumes that of the human to be the same. Chevenix 
states the sp. gr. of the human lens to be 1:079; of the sheep 
1:180.* These experiments are too few in number to be relied 
upon. ‘To determine the density of the lens in various crea- 
tures I have taken the specific gravity of a great number. 
The following tables will perhaps be thought sufficiently 
extensive ,to enable a fair estimate to be arrived at; more 
especially as these figures are not like those in the former 
tables. They may be taken without hesitation as correct, 
there being no difficulty in taking the sp. gr. of the lens. It 
will be seen that Porterfield in his conjecture was not far 
wrong as to the human lens, and that the average weight of 
Dr. Robertson and mine, for bullock and sheep, wonder- 
fully correspond, considering the individual lenses do not 
* Simon’s ‘ Animal Chemistry,’ vol. ii, p. 419. 
