144 VETERINARY PHYSIOLOGY 



independent set, the true auditory nerve, goes to the saccule 

 and the cochlea. 



The membranous labyrinth has an outer fibrous coat, and 

 inside this a homogeneous layer which is markedly thick- 

 ened where the nerves enter it. It is lined by flattened 

 epithelium, which becomes columnar, and is covered with 

 stiff hair-like processes over the thickenings at the entrance 

 of the nerves. On the top of these hair-like processes lies 

 a little mass of calcareous nodules imbedded in a mucus-like 

 substance, the otoliths. In the fish and some lower animals 

 the otoliths are large structures. 



The terminal neurons of both the vestibule and the 

 cochlea end in dendrites between the hair cells, and the 

 cell of these neurons is upon their course to the medulla. 



5. Connection with the Central Nervous System 



The VIII. nerve is essentially double, consisting of a 

 dorsal coehlear or auditory part, and a ventral labyrinthine or 

 vestibular part. 



Coehlear Root (fig. 72). This is the true nerve of hear- 

 ing. Its fibres (Coch.R.) begin in dendrites between the hair 

 cells of the organ of Corti, have a cell upon their course, and 

 when they enter the medulla branch into two divisions, 

 which end either in the tuberculum acusticum or the nucleus 

 accessorius (N.Acc.), where they form synapses. From the 

 cells, axons pass (a) to the oculo-motor mechanism of the 

 same side and the opposite side (N. vi.), and (&) up to the 

 cerebrum (CB. ) of the same and of the opposite side. 



Vestibular Root (fig. 73). The fibres of this root take origin 

 in dendrites between the cells of the maculae in the ampulla? 

 of the semi-circular canals and of the saccule, and have their 

 nerve cells upon their course (Ves.E.). As they enter the 

 medulla they divide into two, forming an ascending and a 

 descending branch. (1) The ascending branch sends fibres on 

 to the cerebrum (CB.}, and to the superior vermis of the 

 cerebellum (CBL.}. These fibres give off collaterals to the 

 nucleus of Deiters (N.Deit.\ from the cells of which fibres 

 pass, which divide, some running on the same side, some on 

 the opposite side ; one branch passing up to the oculo-motor 



