CH. XLVI.] THE SEVENTH NERVE 675 



the other grows central wards ; on reaching the pons these bifurcate, 

 the ascending branches arborise around the principal sensory nucleus 

 of the fifth (yd, fig. 408), which lies just lateral to the motor nucleus, 

 while the descending branches pass down into the bulb, where they 

 form the descending root of the fifth, and some reach as far down 

 in the spinal cord as the second cervical nerve. Mingled with these 

 descending fibres are numerous nerve-cells, many of which are grouped 

 in clusters (islands of Calleja), and the descending fibres form synapses 

 around them. The new axons arising from the cells of the sensory 

 nuclei pass upwards in three principal tracts: (1) The greater 

 number cross the raphe and join the mesial fillet ; (2) some ascend 

 the fillet of the same side ; and (3) others pass into a special ascending 

 bundle which lies near the ventricular floor (the central tract of the 

 cranial sensory nerves). 



The seventh nerve (facial) 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 

 muscles 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 paralysed 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 palpe- 

 brarum. 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 ; in trying to suck, one side only of the mouth acts ; 

 in feeding, on account of paralysis of the buccinator muscle, food 

 lodges between the cheek and gums. 



The motor fibres originate from a nucleus in the ventricular floor 

 below that of the fifth and to the outer side of that of the sixth 

 nerve. As they curve over the nucleus of the sixth, they give off a 

 bundle of fine fibres which cross the raphe, but their destination is 

 unknown. The facial nucleus receives collaterals from the sensory 

 tracts in the reticular formation. 



The seventh nerve, however, is not wholly motor. The geniculate 

 ganglion on it is of spinal type ; the fibres which arise from it pass 

 centrally into the pars intermedia of Wrisberg, which enters the pons 

 between the seventh and eighth nerves ; these, like other sensory fibres, 

 divide into ascending and descending branches ; the latter have been 

 traced down to the sensory nucleus of the glosso-pharyngeal nerve. 

 The peripheral branches of the geniculate ganglion cells pass into the 

 large superficial petrosal and chorda tympani, the gustatory fibres of 

 which they probably furnish. The secretory fibres of the chorda 



