GEXEEAL DISTRIBUTIOX. 523 



grouped together in one foramen. The numerous small olfactory nerves- 

 descend into tlie nose through the cribriform plate of the ethmoid bone ; 

 the optic nerve pierces the root of the lesser wing of the sphenoid bone; 

 the third, fourth, and sixth nerves, with the ophthalmic division of the 

 fifth nerve, pass through the sphenoidal fissure ; the superior maxillary 

 and inferior maxillary divisions of the fifth pass respectively through 

 the foramen rotundum and foramen ovale of the great wing of the 

 sphenoid ; the facial and auditory nerves pierce the petrous bone ; the 

 glossopharyngeal, pneumogastric, and spinal accessory nerves descend in 

 separate canals of the dura mater through the anterior part of the jugu- 

 lar foramen between the petrous and occipital bones ; and the hypoglossal 

 nerve passes through the anterior condylar foramen of the occipital bone. 



General distribution. — The greater number of the cranial nerves 

 are entirely confined in their distribution within the limits of the head ; 

 as in the case of the first six pairs and the auditory nerve. Of these, 

 the olfactory, optic, and auditory are restricted to their respective 

 organs of sense : while the third, fourth, and sixth are exclusively 

 motor nerves in connection with the external and internal muscles of 

 the eyeball and the elevator of the upper eyelid. In the remaining 

 nerve, the fifth or trifacial, all the fibres derived from the greater root, 

 and connected with the Gasserian ganglion, are entirely sensory in their 

 function, and constitute the whole of the first and second and the greater 

 part of the third division of the nerve : but the last of these divisions 

 has associated with it the fibres of the lesser or motor root, so as to 

 become in some degree a compound nerve. As a nerve of sensation the 

 trifacial occupies in its distribution the greater part of the head super- 

 ficially and deeply, excepting the interior of the cranium and that part 

 of the scalp which is situated in the region behind a perpendicular line 

 passing througli the external auditory meatus. The muscular distri- 

 bution of the inferior division of the fifth nerve is chiefly to the muscles 

 of mastication. 



Of the remaining nerves, the facial and hypoglossal, both exclusively 

 motor in function, are almost entirely cephalic" in their distribution ; 

 the facial nerve giving fibres to all the superficial and a few of the 

 deeper muscles of the head and face; and the ninth or hypoglossal 

 supplying the muscles of the tongue. Of the facial, however, a small 

 branch joins one of the cervical nerves in the platysma myoides ; and 

 of the ninth, the descending branch supplies in part the muscles of the 

 neck which depress the hyoid bone and larynx. 



Of the three parts of the eighth pair, ranked as cranial nerves in 

 consequence of their passmg through one of the foramina of the cranium, 

 two, the pneumogastric and spinal accessory, have only a very limited 

 distribution in the head, and furnish nerves in much greater proportion 

 to organs situated in the neck and thorax. The first of these, after 

 giving a small branch to the ear-passages, and supplying nerves to the 

 larynx and pharynx, the trachea, gullet, the lungs and heart, extends 

 into the abdominal cavity as the principal nerve of the stomach. The 

 other, the spinal accessory, which is partially united with the glosso- 

 pharyngeal and pneumogastric near their origin and thus furnishes 

 some of their motor fibres, is entirely a motor nerve, and is distributed 

 in the sterno-mastoid and trapezius muscles. The glosso-pharyngeal 

 nerve is more strictly confined to the head, supplying branches to the 

 tongue, pharynx, and part of the ear passages. 



