THE CEANIAL OR ENCEPHALIC NERVES. 723 



small, forms part of the facial nerve, on which it only presents a kind of 

 intumescence. We have never seen the sharp and precise limitation of its 

 base that is figured in the majority of iconographies of human anatomy. 



On the other hand, when, on portions steeped for several weeks in water 

 acidulated by nitric acid, we have studied the constitution of the great 

 petrous nerve, even at its origin, we have found it formed of two fasciculi 

 very easily separated one internal, the other external : the latter alone is 

 continuous with the geniculated ganglion ; the other traverses the facial 

 nerve from before to behind, then it is suddenly inflected inwards to ascend to 

 the origin of the nerve, and mix with its fibres ; but this fasciculus very often 

 maintains its independence to the medulla oblongata, into which its fibres 

 penetrate separately ; they then appear as a small particular trunk beside 

 that of the principal nerve, and comprised between it and the auditory. 

 The great petrous nerve does not, therefore, proceed exclusively from the 

 ganglion geniculare, as considerable portions of its fibres, entirely destitute 

 of ganglionic corpuscles, emerge directly from the facial nerve. With 

 regard to the external fasciculus, the separation of its fibres by the action of 

 the acid shows very plainly that the grey substance of the ganglion is found 

 almost exclusively on their track ; and if we trace these fibres, like those of 

 the preceding fasciculus, into the substance of the facial nerve, we will find 

 that, instead of proceeding towards its origin, they appear to be directed 

 to its termination: a remarkable circumstance, which we believe may be 

 explained by admitting that they come from the anastomosing branch of the 

 pneumogastric nerve, of which we will speak hereafter. 



From this arrangement, it results that the great petrous nerve arises 

 from the facial by two real, though intimately connected, roots : the internal 

 is evidently motor ; the internal possesses the ganglionic corpuscles of a 

 sensitive root ; and the trunk they both form may be regarded as a mixed 

 nerve. 



As will be observed, our view of the ganglion geniculare differs from 

 the general opinion with regard to it, inasmuch as we make it belong 

 exclusively to the great petrous nerve, and not to the whole of the facial 

 fasciculi. On the other hand, the portio intermedia of Wrisberg is not, in our 

 opinion, the sensitive root of the facial, whose fibres we only look upon as 

 motor ; it is not even that of the great superficial petrous nerve, of which it 

 might at the most be considered as only an accessory filament. In the Horse, 

 this ramuscule is extremely attenuated, and can scarcely, if at all, be dis- 

 tinguished at its origin from the filaments of the lateral root of the auditory 

 nerve ; it is seen to enter the aqueduct of Fallopius, and divide on the bend 

 (or gangliform enlargement) of the facial nerve into several gradually 

 diminishing filaments, which are confounded with the proper fibres of this 

 nerve, or the ganglion geniculare. 



What a difference there is between this arrangement and that of the 

 veritable sensitive roots opposite the ganglia placed on their track ! Why 

 hesitate to admit that this nerve of Wrisberg is on y an anastomosing twig 

 passing from the auditory nerve to the facial ? Is it because of the radical 

 difference in the properties of the two nerves ? Nature, in bringing them so 

 closely together, does not appear to have taken into account this difference ; 

 and the reason for this anastomosis might be explained by the connections 

 the seventh pair maintains with the active portions of the auditory apparatus. 



Is it not the facial nerve that animates the stapedius muscle, and, in an 

 indirect manner, that of the malleus ? Are all the muscles of the external ear 

 not under its influence ? In the present state of science it would be difficult 



