226 



THE CRANIAL NERVES. 



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

 and deeply, excepting that part of the scalp which is situated 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 mastication. 

 The glosso-pharyngeal is also a mixed nerve, and is distributed to the tongue, 

 pharynx, and part of the ear-passages ; while the hypoglossal is purely a motor 

 nerve, destined for the muscles of the tongue, its so-called " descending" and other 

 branches, which supply in part the muscles connected with the hyoid bone, being 

 composed of fibres derived from the upper spinal nerves. 



Fig. 143. SKETCH OF THE MIDDLE POR- 

 TION OF THE BASE OF THE SKULL, 

 SHOWING THE ENTRANCE OP THK 

 CRANIAL NERVES INTO THE DURA 



MATER. (Drawn by T. W. P. 

 Lawrence.) 



The tentorium has bsen divided close 

 to its attachment to the upper border of 

 the petrous. On the right side the nerves 

 are in place ; on the left side they have 

 been removed, and the apertures in the 

 dura mater are seen. 



Of the remaining nerves, one, 

 the facial, mainly if not exclu- 

 sively motor in function, 1 is almost 

 entirely cephalic in its distribu- 

 tion, giving fibres to all the 

 superficial and a few of the deeper 

 muscles of the head ; but one 

 branch passes downwards in the 

 neck to the platysma myoides. 



Lastly, the tenth or pneumo- 

 gastric and the eleventh or spinal 

 accessory nerves differ from the 

 foregoing in having only a very 

 limited distribution in the head, 

 and in furnishing nerves in 

 much greater proportion to 

 organs situated in the neck and 

 trunk. The first of these, after 

 giving a small branch to the ex- 

 ternal ear, and supplying nerves to the pharynx and larynx, the trachea, gullet, 

 lungs and heart, extends into the abdominal cavity as the principal nerve of the 

 stomach. The other, the spinal accessory, which is classed with the cranial nerves 

 in consequence of its passing out through one of the foramina of the skull, is 

 entirely a motor nerve ; it is partially united with the pneumo-gastric near its 

 origin, and thus furnishes some of the motor fibres of that nerve, but it is mainly 

 distributed in the sterno-mastoid and trapezius muscles. 



P On pages 224 and 225, fig. 142 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 



1 It is possible that the chorda tympani branch of the facial may convey sensory (taste) fibres from 

 the tongue. 



LI&.DENTIC. 



