THE CEREBRO-SPINAL SYSTEM OF NERVES. 629 
branches of distribution pass to the following muscles: 1. All 
of the muscles attached to the eyeball, with exception of the 
external rectus and the superior oblique. 2. The levator pal- 
pebre. 3. The circular muscle of the iris, 4, The ciliary 
muscle. Both the latter branches reach the muscles by the 
ciliary nerves, as they pass from the lenticular (ciliary, ophthal- 
mic) ganglion. The relation of the third nerve, as seen in the 
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 dilata- 
tion 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 peculiar 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 easily seen on looking. at a subject thus affected. The 
double image appears when the eyes are directed downward, 
and appears oblique and lower than that seen by the unaffected 
eye. 
The Abductor or Sixth Nerve.—Arising on the floor 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.—lIt 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 supplies, 
(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, 
