GENERAL DISTRIBUTION. 589 



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 ; the facial and auditory nerves pierce the petrous 

 bone ; the three parts of the eighth pair descend in separate canals of the 

 dura mater through the anterior part of the jugular foramen between the 

 petrous and occipital bones ; and the hypoglossal nerve passes through the 

 anterior condyloid foramen of the occipital bone. 



General distribution. The greater number of the cranial nerves are en- 

 tirely 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 that of the upper eye- 

 lid. In the remaining nerve, the fifth or trifacial, all the fibres derived 

 from the greater root, and connected with the Gasseriau ganglion, are en- 

 tirely 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 root, 

 so as to become in some degree a compound nerve. As a nerve of sensa- 

 tion the trifacial occupies in its distribution the greater part of the head 

 superficially 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 through the external auditory meatus. The muscular distribution 

 of the inferior division of the fifth nerve is chiefly to the muscles of masti- 

 cation. 



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 conse- 

 quence of their passing through one of the foramina of the cranium, two have 

 only a very limited distribution in the head, and furnish nerves in much 

 greater proportion to organs situated in the neck and thorax. One of these, 

 the pneurno-gastric, after giving a small branch to the ear-passages, and sup- 

 plying 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 gloss o-pharyngeal and pneumo-gastric near their origin and thus furnishes 

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

 the steruo-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. 



On the following two pages, Fig. 400 is introduced in illustration of the general 

 view of the distribution above given. In this figure the cranium and orbit have been 

 opened up to the depth of the several foramina through which the nerves pass. The 

 greater part of the lower jaw has also been removed on the left side, and the tongue, 

 pharynx, and larynx are partially in view. The occipital bone has been divided by an 

 incision passing down from the occipital tuberosity and through the condyle to the 

 left of the foramen magnum. The cervical vertebrae have been divided to the left of 



