582 COMPARATIVE PHYSIOLOGY. 



changes of the pupil with the movements of the eyeballs, has 

 already been noticed. 



Pathological. — It follows that section or lesion of the third 

 nerve must give rise to the following symptoms : 1. Drooping 

 of the upper lid (ptosis). 2. Fixed position of the eye in the 

 outer angle of the orbit (luscitas). 3. Immobility, with the dila- 

 tation of the pupil (mydriasis). 4, Loss of accommodation. 



The Trochlear or Fourth Nerve.— This nerve, arising in the 

 aqueduct of Sylvius, passes to the superior oblique muscle. 



Pathological. — Lesion of this nerve leads to pecidiar changes. 

 As there is double vision, some alteration must have occurred 

 in the usual position of the globe of the eye, though this is not 

 easUy seen on looking at a subject thus affected. The doiible 

 image appears when the eyes are directed downward, and ap- 

 pears oblique and lower than that seen by the unaffected eye. 



The Abductor or Sixth Nerve.— Arising on the iioor of the 

 fourth ventricle, it passes to the external rectus of the eyeball, 

 thus with the third and fourth nerve completing the innerva- 

 tion of the external ocular muscles (extrinsic muscles). 



Pathological. — Lesion of this nerve causes paralysis of the 

 above-mentioned muscle, and consequently internal squint 

 (strabismus). 



The Facial, Portia Dura, or Seventh Nerve.— It arises in a 

 gray nucleus in the floor of the fourth ventricle, and has an 

 extensive distribution to the muscles of the face, and may be 

 regarded, in fact, as the nerve of the facial muscles, since it sup- 

 plies (1) the muscles of expression, as those of the forehead, 

 eyelids, nose, cheek, mouth, chin, outer ear, etc., and (2) certain 

 muscles of mastication, as the buccinator, posterior belly of the 

 digastric, the stylohyoid, and also (3) to the stapedius, with 

 branches to the soft palate and uvula. 



Pathological. — It follows that paralysis of this nerve must 

 give rise to marked facial distortion, loss of expression, and 

 flattening of the features, as well as possibly some deficiency in 

 hearing, smelling, and swallowing. Mastication is difficult, 

 and the food not readily retained in the mouth. Speech is 

 affected from paralysis of the lips, etc. 



Secretory fibers proceed (1) to the parotoid gland by the 

 superficial petrosal nerve, thence (2) to the otic ganglion, from 

 which the fibers pass by the auriculo-temporal nerve to the 

 gland. 



Gustatory Fibers. — According to some, the chorda tympani 



