On the means employed for correcting the inverted image on the retina of the eye / by Joseph Swan.

  • Swan, Joseph, 1791-1874.
Date:
1865
Catalogue details

Licence: Public Domain Mark

Credit: On the means employed for correcting the inverted image on the retina of the eye / by Joseph Swan. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    reaching the retina, so that the superior margin is placed below, whilst the inferior becomes upper- most ; the right side is depicted to the left, and the left to the right. The image of an object placed upside down becomes erect on the retina, but on reaching the brain is restored to its exterior reversed position. Although the eye, by the deflecting power of the lens and humours, in reality reverses the position of exterior objects, they are only in progres- sion to be restored to their original characters by the arrangements of the nerves and tracts through which they are to be conducted by their centres and the convolutions of the brain to the sensory. Although the remarkable semicircular position of the optic tract in its descent from the posterior part of the thalamus over the crus of the brain to the optic commissure has been described by anatomists, the uses of the disposition of the fibres have been very seldom adverted to.* Their form and arrange- ment are evidently adapted for allowing the conve- nient position of the eye at the frontal and lateral aspect of the head and face, and for being adapted to the various parts with which it is intended to co-operate for completing vision. If the fibres of the optic tract had been carried in a du-ectly straight line from the posterior part of the thalamus, they would have terminated near the back of the head. For allowing the eye, therefore, to be placed in its ♦ After this paper had been corrected for the press an instance was found in The Nervous System, by Alexander Walker, p. 187.