THE NERVOUS SYSTEM. 



and No. 2 (also seen in both Figures), is the 2d or optic nerve, that 

 goes to the eye, and gives the power of vision. 



No. 3 (seen in both Figures) is a nerve that goes exclusively to 

 the muscle of the eye. It has its origin from the anterior column 

 of the spinal cord, which runs up to the cerebrum, and is, therefore, 

 only a nerve of motion. 



No. 4 (seen in both Figures) is the smallest nerve in the body, 

 being, in man, little thicker than a sewing thread. It goes to a 

 single muscle which moves the eye (trochleator) ; it is a nerve of 

 motion, and probably has an origin similar to the last, though this 

 has not been distinctly shown. 



No. 5 (seen in both Figures, but best in Fig. 32) is a most exten- 

 sive and important nerve. It is the highest that arises by double 

 roots, and is, as shown by Sir Charles Bell, both a motor and a 

 sensitive nerve. Its first branch (Fig. 32, 5), which goes to the eye, 

 eyebrows, forehead, &c., comes only from the posterior or sensitive 

 root, and gives to the parts mentioned the sense of touch or com- 

 mon sensation. If this nerve were destroyed, we might have sensa- 

 tions from light, but we could have no feeling when anything else 

 came in contact with the eye. The second branch (Fig. 32, 5'), 

 like the first, comes from the posterior root, and gives sensibility to 

 the upper jaw, palate, upper lip, &c. The third branch (Fig. 32, 

 5") has its origin from both the motor and sensitive roots, and hence 

 gives both sensibility and the power of motion. It goes to the 

 muscles, skin, &c., connected with the lower jaw, tongue, and 

 mouth. The sensitive branches of the 5th nerve are those that are 

 so painfully affected in toothache and tic doloureux. 



No. 6 (Figs. 32 and 33) is the 6th nerve. It has only one root 

 from the anterior part of the spinal cord, and is hence exclusively 

 a motor nerve. It goes to a single muscle of the eye. 



No. 7 (Figs. 32 and 33) is the motor, or hard portion, as it is 

 sometimes called (portio dura), of the 7th nerve. It is extensively 

 distributed to the muscles of the face and forehead. When it is 

 cut, the muscles on that side are paralysed, and the mouth, as for- 

 merly noticed, is drawn to the other side. 



No. 7' (Fig. 32) is called the soft portion of the 7th nerve. It 

 goes to the internal ear, and is the nerve of hearing. 



No. 8 (Figs. 32 and 33) is called the glossopharyngeal nerve, 

 from being distributed to the root of the tongue and pharynx. The 

 functions of this nerve are at present the subject of dispute. 



No. 8' (Figs-. 32 and 33) are called the pneumogastric nerves, 



