ENUMERATION OP CRANIAL NERVES. 135 



2d pair. Optic nerves, which preside over the organs of 

 sight. Its terminal expansion forms the retina. 



3d pair. The common oculo-motor nerves, which are dis- 

 tributed to most of the muscles which move the eyeball. 



4th pair. Pathetic nerves, so called, because they give the 

 power of motion to the great oblique muscle, the action of 

 which, upon the eyeball, is one of the principal elements in 

 the expression of the face. 



5th pair. The trigeminal or trifacial nerve forms on 

 either side three nerves, the ophthalmic and the superior 

 and inferior maxillary; they are distributed over the face, 

 and to the organs which constitute it. 



6th pair. The external oculo-motor nerves. These go to 

 the external straight muscle of each eyeball. The 



yth pair is divided into the hard portion or facial nerve, 

 which goes to the face, and the soft portion or auditory nerve, 

 which goes to the internal ear. The 



8th pair is divided into three branches: i. the glosso-pha- 

 ryngeal, the nerve of taste, running to* the tongue and pharynx, 

 and furnishing branches to several muscles of the neck, to the 

 tonsils, &c. 2. The pneumo-gastric nerve, which branches 

 out to the cervical region, to the pharynx, the larynx, the 

 lungs, and the stomach. 3. The spinal accessory of Willis, 

 which sends branches to several muscles of the neck, to the 

 pharynx, and to the larynx. 



9th pair. The great hypoglossal nerves, which give move- 

 ment to the tongue. 



The spinal nerves form eight cervical pairs, twelve dorsal, 

 five lumbar, and six sacral. They all spring from the spinal 

 cord in two bundles of roots, called the anterior and posterior 

 roots, according to the portion of the cord from which they 

 emerge. These roots are enveloped in a membranous sheath, 

 and unite to form the trunk of the nerve at a point more or 

 less distant from their origin, according to the region from 

 which they proceed. The roots of the lumbar and sacral 

 nerves form a bundle of independent cords in the inferior 

 portion of the spinal canal, which, from their peculiar dis- 

 position, has been named the cauda equina or horse-tail. 



On a level with the openings through which the nerves 



