264 rV PHYSIOLOGY FOR DKNTAL STIDKNTS. 



lulitis of this gland, and on account of its superficial position, 

 it may be injured by blows on the side of the head. Quite com- 

 monly the seventh nerve becomes the seat of inflammation after 

 exposure to a draught, as by sitting at an open window. The 

 l>r(i lysis is almost always one-sided. The eyelid on the affected 

 side cannot be properly closed, a chink remains and the eyeball 

 becomes rotated upward, thus showing the sclerotic. On smiling 

 or showing the teeth the mouth is drawn up on the healthy side. 

 causing a triangular opening because the lips do not become 

 separated on the paralyzed side. Articulation is difficult and 

 such acts as whistling and blowing are impossible. Because of 

 paralysis of the buccinator muscle, food collects between the 

 cheek and gums. The distortion of the face is much more pro- 

 nounced in old, than in young persons; indeed in the case of 

 the latter the paralysis may be overlooked until speaking or 

 laughing is attempted. 



THE EIGHTH OR AUDITORY NERVE. The eighth or auditory 

 nerve is composed of two branches, the one called cachluir, con- 

 nected with the organ of Corti (see p. 291), which collects sound 

 waves, and the other, called vcstibular, with the semicircular 

 canals which, by the movements of the fluid contained in them, 

 record changes in the position of the head (see p. 276). Both 

 branches, being sensory, are connected with ganglia situated in 

 or near the internal ear (ganglion spirale for the cochlear di- 

 vision and ganglion of Scarpa for the vestibular). Paralysis 

 of the auditory nerve causes a degree of deafness which is more 

 profound than that due to disease of the middle ear, for in the 

 latter case a tuning fork can be heard when the end of it is 

 applied to the skull or is held in the teeth, which is not the case 

 when the nerve is diseased. When the eighth nerve becomes 

 irritated (as by inflammation of the ear, or a general condition 

 such as migraine, epilepsy, etc.), various kinds of sounds are 

 heard. This is called tiiittitits. It is not infrequently followed 

 by deafness. 



THE NINTH OR GLOSSO-PIIARYNGEAL NERVE. The ninth or 

 glosso-pharyngeal nerve is partly motor and partly sensory. 

 The motor fibers supply the muscles of the pharynx and most of 



