ACTION OF THE MUSCLES OF THE EYEBALL. 249 



course, be moved in the direction of the diagonal between the two 

 forces; and if each muscle contracts rapidly after the other, the 

 organ will execute a movement of circumduction. The oblique mus- 

 cles are in some respects antagonists to each other, and roll the eye in 

 opposite directions; the superior oblique directing the pupil down- 

 wards and inwards ; the inferior upwards and inwards. But as the 

 different straight muscles are capable of carrying the eye in these di- 

 rections, were we to regard the two sets of muscles as possessing ana- 

 logous functions, the oblique would appear to be superfluous. This, 

 along with other reasons, attracted the attention of Sir Charles Bell 

 to the subject; and the result of his experiments and reflections was ; 

 that the straight muscles are concerned in the motions of the eye 

 excited by volition : and that the oblique muscles are the organs of its 

 involuntary motions. In this manner, he accounts for several pheno- 

 mena, connected with the play of the organs in health and disease. 

 Whilst the power of volition can be exerted over the recti muscles, the 

 eye is moved about, in the waking state, by their agency; but, as soon 

 as volition fails from any cause, the straight muscles cease to act, and 

 the eye is turned up under the upper eyelid. Hence this happens at 

 the approach of, and during sleep; and whenever insensibility occurs 

 from any cause, as in faintness, or on the approach of dissolution; and 

 the turning up of the eyeball, which we have been accustomed to re- 

 gard as the expression of agony, is but the indication of a state of in- 

 cipient or total insensibility. Whenever, too, the eyelids are closed, 

 the eyeball is moved, so that the cornea is raised under the upper eye- 

 lid. If one eye be fixed upon an object, and the other be closed with 

 the finger so placed as to feel the convexity of the cornea through the 

 upper eyelid, and the open eye be shut, the cornea of the other eye 

 will be found to be elevated. This change takes place during the most 

 rapid winking motions of the eyelids ; and is obviously inservient to 

 the protection of the eye ; to the clearing of the eyeball of everything 

 that could obscure vision, and perhaps, as Sir Charles Bell presumes, 

 to procure the discharge from the Bluets of the lachrymal gland. Dur- 

 ing sleep, when the closure of the eye is prolonged, the transparent 

 cornea is, by this action, turned up under the upper eyelid, where it is 

 securely lodged and kept moist by the secretions of the lachrymal 

 gland, follicles, and conjunctiva. 



The different distributions of the motor nerves of the eye have been 

 described in the anatomical sketch. It was there stated, that the supe- 

 rior oblique muscle receives one whole pair of nerves, the fourth. 

 This nerve, then, it seemed to Sir Charles Bell, must be concerned in 

 the functions we have described; and, as the various involuntary 

 motions of the eyeball are intimately concerned in expression, as in 

 bodily pain, and in mental agony, in which the action of the direct 

 muscles seems, for a time, to be suspended, he was led to consider 

 the fourth as a nerve of expression, a respiratory nerve; and, 

 hence, intimately connected with the facial of the seventh pair, which, 

 as has been already remarked, is the great nervous agent in the 

 twinkling of the eyelids. Anatomical examination confirmed this 

 view: the roots of the nerve being found to arise from the same co- 



