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;^OOLOGY 



SECT. 



Fig. TS!'. — Longitudinal section through !in auipulla. c. t. auditory 

 epithelium ; a. h. auditory hairs ; c. pm-t of semicircular canal ; 

 c.v. crista acustica ; ct. connective-tissue ; e. ?, epithelium : ;»_. 

 nerve; v.. junction with utriculus. (From Foster and Shore's 

 Vlq/siology.) 



otoliths of varying- size and number. There is every reason fur 

 thinking that the labyrinth, like the otocysts or statocysts in the 

 lower animals, functions as an onjnn of equilibration as v/ell as of 

 hearing. 



As the membranous labyrinth develops in the embryo, it be- 

 comes surrounded and enclosed by the auditory capsule, the 



cartilage of which 

 adapts itself to the 

 form of the hiby- 

 rinth, presenting a 

 large excavation 

 for the utricle and 

 saccule and tun- 

 nel-like passages 

 for the canals. The 

 auditory organ 

 does not, however, 

 iit tightly into 

 this system of 

 cavities, but be- 

 tween it and the 

 cartilage is a space, 

 filled by a fluid 

 called i)Gril!jm]i)li, 

 which acts as a buffer to the delicate organ floating in it. 



The early history of the auditory apparatus in the embrj-o 

 shows that it belongs to the same series of structures as the lateral- 

 line system, of which it may be regarded as a highly specialised part. 

 Nerve-components. ^ — The nerve-fibres of which the nerves — 

 cerebral, spinal, and sympathetic — are made up, the oicrvc- 

 components as they are termed, are capable of being classified in 

 accordance with the nature of the functions which they perform. 

 A broad division into motor and sensory fibres has already been 

 referred to. A more detailed classification is the following : — 



Division I. — Somatic sensory, comprising (a) the fibres which 

 have to do with general cutaneous or tactile sensations ; (h) those 

 connected with the neuromast organs and with the auditory 

 organs ; ('■) the fibres of the optic nerves. 



Division II. — Ftsccra/ w/iswy, comprising (a) the fibres which 

 end in visceral mucosae and have to do with vi.sceral sensations ; 

 (h) the fibres ending in taste-buds ; ('■) those which terminate in 

 the olfactory epithelium. 



Division III. — Somatic motor, consisting of components which 

 terminate in somatic musculature. 



Division IV. — Visceral vwior, comprising all fibres which 

 terminate in visceral musculature and have to do with visceral 

 movements. 



