CH. XLIV.] THE CRANIAL NERVES. 627 



deep origin is also double. The motor centre is internal to the 

 sensory, and from it reach a number of fibres stretching 

 upwards as far as the anterior corpus quadrigeminum ; this is 

 termed its descending root ; it is also connected with the locus 

 cceruleus. The sensory centre or nucleus outside the motor has 

 connected with it a tract of fibres from the cord as low as the 

 second cervical nerve (ascending root). 



7. Facial. This is the great motor nerve of the face muscles. 

 It also supplies the platysma, the stapedius, stylo-hyoid, and 

 posterior belly of the digastric. When it is paralysed, the mus- 

 cles of the face being all powerless, the countenance acquires on 

 the paralysed side a characteristic, vacant look, from the absence 

 of all expression : the angle of the mouth is lower, and the para- 

 lysed half of the mouth looks longer than that on the other side ; 

 the eye has an unmeaning stare, owing to the paralysis of the 

 orbicularis palpebrarum. All these peculiarities are exaggerated 

 when at any time the muscles of the opposite side of the face 

 are made active in any expression, or in any of their ordinary 

 functions. In an attempt to blow or whistle, one side of the mouth 

 and cheeks acts properly, but the other side is motionless, or flaps 

 loosely at the impulse of the expired air ; so in trying to suck, 

 one side only of the mouth acts ; in feeding, the lips and cheek 

 are powerless, and on account of paralysis of the buccinator 

 muscle, food lodges between the cheek and gums. 



The deep origin of this nerve is shown in the diagram below 

 that of the fifth, and to the outer side of that of the sixth nerve. 



The chorda tympani, which is generally described as a branch 

 of this nerve, is probably a continuation of the pars intermedia, 

 which is connected with the upper part of the glosso-pharyngeal 

 nucleus. 



8. Auditory. This nerve leaves the hinder margin of the pons 

 by two roots. One winds round the restiform body dorsal to it, 

 and the other passes ventro-mesially on the other side of the 

 restiform body. The former is called the dorsal root. The latter 

 is called the ventral root. The dorsal root contains a large 

 number of nerve-cells, which give origin to many of its fibres. 

 Ventral to the restiform body and between the two roots is 

 another mass of ganglion cells, the accessory auditory nucleus. 

 Higher up these two collections of cells blend to form a ventral 

 nitclni*, for this division of the auditory nerve. Some of the 

 fibres of this root are superficial in position, and form the stria* 

 acusticff across the ventricular floor. This root becomes the 

 cochlear branch of the auditory nerve ; it is the auditory nerve 

 proper, and it is distributed to the cochlea of the internal 



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