Chap. VILj THE NERVOUS SYSTEM. 89 



9. Glossopharyngeal (mixed). 



10. Pneumo-gastric or Vagus (mixed). 



11. Spinal accessory (motor). 



12. Hypo-glossal (motor). 



The olfactory nerve is the special nerve of the sense of smell. Its origin 

 is in the olfactory bulb. Its peripheral dendrones pass through the perfo- 

 rated plate of the ethmoid bone and are distributed to the mucous mem- 

 brane lining the nasal chambers, while the central axones pass backward to 

 the brain. 



The optic nerve is the special nerve of the sense of sight. Its cell-bodies 

 are situated in the retinal coat of the eye. Part of its central axones ter- 

 minate in the same side of the brain, while the remainder cross to terminate 

 in a similar region on the opposite side of the brain. This crossing of part 

 of the fibres from both eyes forms the optic commissure. 



The oculomotor nerve supplies all the muscles of the eye except the 

 superior oblique and the external rectus. It originates in the gray matter 

 of the pons Varolii. 



The pathetic or trochlear nerve supplies only the superior oblique mus- 

 cle of the eye. It arises close to the preceding nerve. 



The trifacial is the largest of the cranial nerves. Like the spinal nerves 

 it has two roots, — a dorsal or sensory (upon which there is a sensory gan- 

 glion), and a ventral or motor. The fibres from the two roots coalesce into 

 one trunk, and then subdivide into three large branches : the ophthalmic, 

 the superior maxillary, and the inferior maxillary. The ophthalmic branch 

 is the smallest, and is a sensory nerve. It supplies the eyeball, the lachry- 

 mal gland, the mucous lining of the eye and nose, and the skin and muscles 

 of the eyebi'ow, forehead, and nose. The superior maxillary, the second 

 division of the fifth, is also a sensory nerve and supplies the skin of the 

 temple and cheek, the upper teeth, and the mucous lining of the mouth and 

 pharynx. The inferior maxillary is the largest of the three divisions of the 

 fifth, and is both a sensory and a motor nerve. It sends branches to the 

 temple and the external ear ; to the teeth and lower jaw ; to the muscles of 

 mastication ; it also supplies the tongue with a special nerve (the lingual) 

 of the sense of taste. The cell-bodies of the motor fibres are situated in 

 the pons; while those of the sensory fibres, as in the case of the spinal 

 nerves, are situated in a ganglion. This ganglion is called the Gasserian 

 ganglion. 



The abducens nerve supplies the external rectus muscle of the eye. 



The facial nerve is the motor nerve of all the muscles of expression in 

 the face ; it also supplies the neck and ear. Its cells of origin, like those of 

 the abducens nerve, are situated in the medulla. 



The auditory nei-ve is the special nerve of the sense of hearing. It 

 arises from cells which compose the spiral ganglion in the internal ear, to 

 •which its dendrones are exclusively distributed. 



The glosso -pharyngeal nerve is distributed, as its name indicates, to the 

 tongue and pharynx, being the nerve of sensation to the mucous membrane 



