CHAP. XVIII.] 



HEARING. 



85 



Fig. 144. 



Termination 01 the nerve in the ampulla of a ray, highly magnified. (From Wagner.) 



Of the Auditory Nerve. The portio mollis of the seventh pair has 

 its origin from the medulla oblongata by two roots. One penetrates 

 to the central part of the medulla oblongata in the same way, and fol- 

 lowing the same direction, as the portio dura, but passing to a much 

 greater depth into its substance. The other winds round the corpus 

 restiforme, not penetrating it, but simply adhering to its surface, 

 until it reaches the floor of the fourth ventricle, where it connects 

 itself with the olivary columns, and in many instances is evidently 

 continuous with the white striae on either side of the calamus scrip- 

 torius, which for that reason have been very generally regarded as 

 fascicles of origin of the portio mollis. 



The portio mollis, when contrasted with the other nerves of the 

 medulla oblongata, is remarkable for its delicacy of structure, a 

 ;haracter which had attracted the attention of the older anatomists 

 and by reason of which they had given the nerve the appellation 



mollis." It has but a very delicate neurilemma, and its fascicles 

 are loosely held together; it seems strictly a direct prolongation of 



le white matter of the brain. 

 The portio mollis enters the internal auditory foramen, and there 



>rms a connexion with the portio dura, by means of a few fascicles 



)f fibres which constitute the " portio intermedia " ofWrisberg. It 



is difficult to say whether this consists of fibres proceeding from 



the auditory to the facial nerve, or from the latter to the former. 



It is most reasonable to suppose that the muscular nerve (the facial) 



