Anatomical and physiological observations. Pt. I / by John Struthers.

  • Struthers, John, 1823-1899.
Date:
1854
Catalogue details

Licence: Public Domain Mark

Credit: Anatomical and physiological observations. Pt. I / by John Struthers. 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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    less directly on their axes, and in a contrary direction, other- wise tlie picture of the object would change its place circularly on the retina. This motion will be more or less combined with those performed by the straight muscles, according as the axis of motion of the head corresponds more or less to that of the eyes; and it may be that the oblique muscles, from their not exactly embracing the middle of the eye transversely, are intended also, and at the same time, to turn the axis of the eye, so as to change, to a certain extent, its direction. It would appear, therefore,—as it is essential to the correct viewing of an object when the head is being moved, that the picture fall in all re- spects on the same part of the retina,—that a more or less direct movement of rotation on the antero-posterior axis is neces- sary; and it may be added, that the nature of this movement— as it causes little or no change in the direction of the eye— together with the circumstances under which it takes place, are such as not to render its occurrence evident to an observer. The circumstances under which this movement would be re- quired in those animals in which the eyes are placed in the side of the head, and look outwards, are different; as, in the simple movement of raising or depressing the head, the latter moves more on an axis corresponding to that of the eyes, so as to render a more direct lateral rotatory motion necessary, in order to prevent the image ft'om changing its place circularly on the retina. In these animals, it is doubtful if the eyes, which can- not be directed together to the same object, are moved simul- taneously; but if so, the corresponding oblique muscles will be employed at the same time on opposite sides, whereas, in the circumstances explained by Hunter, the superior oblique of the one side would be in action along with the inferior of the other. These, however, are so far only theoretical considerations, and do not affect the conclusion to which comparative anatomy points, that the oblique muscles—whatever minor differences may obtain as to their arrangement in different vertebrate ani- mals—are, in all, not only capable of performing this move- ment in opposite directions, but are evidently intended for doing so.