| OCR Text |
Show 1894.] PUPILS OF THE FELID.E. 483 Males Females Gelded Number examined. 55 64 37 Round. 38 32 21 Nearly round. 1 4 3 Rect. Oval. 10 20 9 Acute Oval. 6 8 4 The only condition which appears to have an influence on the shape of the pupil seems to be age. M y observations on the above-mentioned cats, and on a number of others, all lead me to the conclusion that the younger the cats the rarer the cases in which the pupil is round, and conversely, the older the cats the greater the prevalence of round pupils. This I think may be due to a decrease of the elasticity and consequent contractility of the iris as the animals grow older. In no case have I noticed any convergence of the eyes or any contraction of the pupil in accommodation for near objects. Sudden bright illumination, however, invariably causes contraction. The cat's iris contracts in a very definite and curious way. It may be imitated most accurately by causing two discs to overlap, so as to form the figures indicated in the diagrams shown above, until the horizontal diameter is equal to half the vertical (Acute oval), when the contraction ceases in the vertical direction, but continues horizontally until the sides meet, forming two parallel vertical lines in close contact (see fig. 3). At the extremities of this vertical slit there are always two round pinholes, which are caused by the inability of the fibres of the iris to come further together; if examined with a strong magnifying-glass, the radiating fibres of the iris are seen surrounding these points. Fig. 2. Fig. 3. W h e n I held a cat's face so that the unobscured sun shone directly on the centre of the pupil, and its image could be seen on the cornea, I noticed the pupil immediately contract to the above-mentioned vertical slit. So close was the contact between the free margins of the iris that, so far as I could judge, no light entered the eye except through the two pinholes. In fact, I found I could hold a cat with the lids held apart so that the sun shone directly |
