. Elements of physiological psychology; a treatise of the activities and nature of the mind, from the physical and experimental points of view . curved by the action of its own withdrawal of the tension is accomplished by the action of theciliary muscle, the fibres of which have their point of fixation at theedge of the cornea, and run from here in the direction of a merid-ian toward the equator of the eye. When the ciliary muscle con-tracts, the free ends of its fibres are drawn toward its fixed endson the edge of the cornea; the radial tension of the suspensory lig-ament is th
. Elements of physiological psychology; a treatise of the activities and nature of the mind, from the physical and experimental points of view . curved by the action of its own withdrawal of the tension is accomplished by the action of theciliary muscle, the fibres of which have their point of fixation at theedge of the cornea, and run from here in the direction of a merid-ian toward the equator of the eye. When the ciliary muscle con-tracts, the free ends of its fibres are drawn toward its fixed endson the edge of the cornea; the radial tension of the suspensory lig-ament is thus relaxed, and the lens is allowed to assume its naturalform under the equipoise of its own elastic forces (Fig. 76). The iris of the eye corresponds to the diaphragm of the contains two sets of contractile fibres, one circular, the effect ofwhich is to diminish the size of the pupil; the other radial and en-larging the pupil. Contraction of the pupil occurs under two con-ditions: When bright light (or, more exactly, light brighter than that> Beer, Wien&r hlin. Wochenschrift, 1898, XI, 942. MECHANISM OF ACCOMMODATION 189. to which the retina is at the time adapted) enters the eye; and whenthe eye is accommodated for a near object. In both cases the effectof narrowing the pupil is to increase the clearness of vision. A sud-den bright light has a dazzling effect, and this is lessened by di-minishing the quantity of light entering the eye. The divergentrays from a near object are not so well focussed as are the morenearly parallel rays, on account of spherical aberration; but this badeffect is diminished by cutting off the more oblique rays whichenter through the periphery of the fcornea and lens. The nerves which supply the muscles of the eye are the third,fourth, and sixth of the cranial nerves, and the sympathetic. Ofthese, the third or oculomotor is the largest; in it are contained thefibres which supplythe ciliary muscle,and those whichsupply the circularmuscle
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