454 ORGANS OF THE SENSES. 



The study of the muscles of the eye is connected with 

 that of the muscles of the eyelids ; of these there are two 

 muscles : the elevator of the upper eyelid (levator palpebrcB 

 superioris) and the orbicularis palpebrarum. The levator 

 palpebrw, which is over the superior rectus muscle of the eye, 

 seems almost superfluous, for the last-mentioned muscle, by 

 the fibres which connect it with the upper eyelid, would be 

 sufficient to raise the latter at such times as it directs 

 the pupil upwards. The elevator muscle serves, however, to 

 keep the palpcbral aperture wide open, and, during our wak- 

 ing moments, it reposes only for a few seconds at a time, and 

 at irregular variable intervals, when the eyes are closed by 

 winking. The orbicular muscle is, like all other sphincters, 

 formed of fibres in the form of a loop or a circle, but exhibits 

 on every side, and especially on its nasal aspect, genuine 

 insertions in the form of bony adhesions, so that in contracting, 

 the palpebral opening is reduced to a transverse slit, instead 

 of to a point : this is also owing to the fact that the eyelids con- 

 tain, in their substance, thick layers of resisting fibrous tissue 

 (called tar sal cartilages}. The functions of this sphincter 

 appear to be supplementary to that of the orbicular muscle 

 of the iris : like the latter it contracts under the influence of 

 sensations on the retina, as, for instance, when the light is too 

 strong ; but it also contracts under the influence of reflex 

 irritations originating at the cornea. Thus it is extremely 

 difficult to keep the eye open when any foreign body touches 

 the surface of the cornea, and diseases of this surface fre- 

 quently give rise to actual spasms of the eyelids. 



The Lachrymal Apparatus. This is composed of a gland 

 which secretes the lachrymal fluid or tears, eyelids, whose 

 office it is to spread this fluid over the anterior surface of the 

 globe of the eye, and, finally, of a series of tubes, by which 

 the fluid is pumped up, and carried into the nasal chambers. 



The lachrymal gland, which is formed of lobules similar 

 to those of the salivary glands, is situated in the upper part 

 of the outer angle of the eye ; gravitation is sufficient to con- 

 vey the secretion to the external surface of the globe ; this 



muscles of the nose, which are little affected by the will, and only 

 by the contraction of the internal fibres of the frontal .muscle; it is 

 precisely the contraction of the centre of this muscle which raises 

 the inner extremities of the eyebrows, and imparts the character- 

 istic expression of sadness to the face." (Leon Dumont, u Ex- 

 pression des Sentiments, d'apres Darwin," in *' Revue des Cours 

 Scientifiques." Mai, 1873. 



