A treatise on the theory and practice of medicine / by John Syer Bristowe.

  • John Syer Bristowe
Date:
1887
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on the theory and practice of medicine / by John Syer Bristowe. Source: Wellcome Collection.

    1207/1322 (page 1161)
    respond to them (see fig. 106) are (supposing the left eye to be under consideration, and its line of vision to be fixed directly forwards):—for the external and internal recti, a vertical straight line passing through the centre of the eye ; for the superior and inferior recti, a horizontal straight line (r r) passing obliquely through the centre so that its nasal extremity is a little in advance of its temporal extremity, and forming an angle of about 70° with the line of vision ; for the obliqui, another horizontal straight line (o o) passing also obliquely through the centre, but in such a direction that it makes an angle of 35° only with the line of vision—its temporal extremity being just a little beyond the outer margin of the cornea, and its nasal extremity towards the back of the eye, a little in- ternal to the optic disc. It may be assumed as sufficiently accurate for all practical purposes : that the ball of the eye is globular ; that it is lodged in a socket bounded by fat, connective tissue, and membrane, in which it moves as the head of the femur moves in the cotyloid cavity; that its centre of rotation is the actual centre of the eye ; and further, as Helmholtz shows, that in consequence of the fixed origins of the oculo-motor muscles, and their broad insertions, the three axes of rotation which have been indicated remain unalterable in their relation to the fixed points of the orbit, no matter how much the line of vision—the line in which the eye is looking— becomes altered. It follows (see fig. 107) from the above considerations : first, that the internal and external recti always cause the cornea to revolve around a vertical axis, to move therefore either in a horizontal equatorial line, or in proportion as it is elevated or depressed below this line in the arcs of smaller and smaller parallel circles; second, that the superior and inferior ^ recti always cause the cornea to revolve around the oblique horizontal axis, whose position has already been defined, and hence in the arcs of circles which are parallel to a vertical equatorial section of the eyeball, ^ made through or near the outer margin of ^^Y.-hett cycbaii with iiis and the cornea (as the eye looks directly forwards) pupil seen from the front. „ , n XI - • f u i--^ 0, Anterior pole of axis of rotation for 111 front, and the inner margin oi tne optic owiqui; ;•. anterior poie of axis of ro- disc behind, so that the circles to which these upi^S a^low;?^^^^ arcs belong become smaller and smaller fi-om f^^^ mtemRi and external o _ recti, the outer to the inner CantllUS of the eye, and The concentric circles around o and r ■ n n ,1 J- • • x'„„1 respectively indicate the direction the mnuence oi the recti m causing vertical ^,^,1 amount of movement of the movements of the cornea correspondingly ^l^^J^]!^l^!^s^r£^ diminished; third, that the obliqui always ToiyotatHnTsla^^rS^reia! cause the cornea to revolve around the obhque tion ^to the movements about the horizontal axis which has been referred to ' ' these muscles, and hence in the arcs of circles which are parallel^ to a vertical equatorial section of the eyeball, made through or near the inner