CHAPTER W 

 Special Somatic Afferent System. 



THE special somatic afferent division comprises the 

 auditory and vestibular elements and also the visual 

 neurons. It really includes the olfactory neurons in 

 addition to these, though the olfactory functions combine 

 exteroceptive with interoceptive components, and it is usual 

 to consider the olfactory structures with the visceral afferent 

 group. Some authors object to this usage, however. Only 

 the auditory and vestibular systems, which occur in the 

 hindbrain, will be considered in the present chapter. 



The fibres which convey auditory impulses to the brain 

 form the cochlear branch of the eighth nerve, which branch 

 ends in two large nuclei situated superficially on the dorso- 

 lateral aspect of the medulla oblongata in its more anterior 

 part. The dorsal cochlear nucleus {nucleus cochlearis dorsalis) 

 or tuherculum acusticum extends from the dorsal part of the 

 lateral surface round on to the dorsal surface, where it runs 

 medially as far as the edge of the ventricle. It is situated 

 immediately behind the attachment of the cerebellum to 

 the medulla and its ventral end is produced forward along 

 the lateral aspect of the cerebellar peduncles for some dis- 

 tance, where it is continuous with the flocculus. In the 

 angle between the ventral extremity of this nucleus and the 

 side of the oblongata lies another mass of gray matter of a 

 more rounded shape, the ventral cochlear nucleus {nucleus 

 cochlearis ventralis). This does not extend so far posteriorly 

 as the tuberculum acusticum, but reaches considerably farther 



