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VI, On the Anatomical and Optical Structure of the Crystalline Lenses of Animals. 
Continued from a former Paper (Phil. Trans. 1 833, p. 332.). By Sir David 
Brewster, K.H. LL.D. F.R.S. Sec. Sec. 
Received November 26, 1835, — Read January 21, 1836. 
^ 2. On the Anatomical and Optical Structure of the Crystalline Lenses of Animals, 
particularly those of the Hare and the Salmon. 
In describing the various structures which exist in the crystalline lenses of animals, 
I shall proceed from the most simple to the most complex combination of fibres. In 
the paper which I have already submitted to the Society, I took the lens of the cod 
as the type of the first or simplest structure, in which the fibres, like the meridians 
of a globe, converge to two opposite points of a spheroidal or lenticular solid ; and I 
shall now proceed to describe the second or next simplest structure, as exemplified in 
the lenses of the salmon and the hare. 
This structure is shown in Plate IV. fig. 1, Avhere A A is the anterior and B B the 
posterior hemisphere of the spheroidal lens of the salmon. A lens thus constituted is 
said to have two septa at each pole, A and B (fig. 2.), namely, the septa Ah, Ac, and 
B d, B e, in different points of which all the fibres have their origin and termination. 
One of the fibres, for example, which has its origin in A, passes over N, and terminates 
in d ; while the other passes from A to O, and terminates in e. In like manner, the 
fibre which begins at h passes over P, and ends in B ; while the fibre which begins at c 
passes over M, and terminates in B. The different parts of these four fibres lie in 
one plane, like the meridians of a globe. All the other fibres, which have their origin 
between A and B, have their termination between d and B ; and all those which have 
their origin between A and c have their termination between e and B. All these fibres, 
or every fibre in each lamina except four, have their different parts lying in different 
planes, or form curves of contrary flexure. In order to understand this structure, and 
appreciate its beauty, it is necessary to draw the fibres upon a globular surface. A 
perspective view of such a globe is given in fig. 3, where A h is one of the anterior 
septa, -and B c one of the posterior ones. The two curves which go from the poles A 
and B to the ends of the septa c, h, are ellipses, while all the rest are curves of con- 
trary flexure. 
The length of the septa Ah, Ac, &c. varies in different fishes ; and when they are 
very short, as they must necessarily be in small lenses, we are apt to mistake the 
structure which they indicate for that of a diffused polarity round the two extremities 
f 2 
