182 



SENSE OF HEARING. 



Fig. 71. 



without any bony parietes. It exhales at its inner surface a limpid 

 fluid, called liquor or lymph of Cotugno or Cotunnius, perilymph of 

 Breschet, which, under special circumstances, can reflow into the aquse- 

 ductus vestibuli and aquseductus cochleae. This fluid is contained in all 

 the cavities of the internal ear. Within that of the osseous labyrinth 



are contained membranes 

 having nearly the shape of 

 the vestibule and semicir- 

 cular canals, but not ex- 

 tending into the cochlea. 

 These membranes, which 

 compose what has been 

 called the membranous 

 labyrinth, form a continu- 

 ous but close sac, contain- 

 ing a fluid, endolymph, 

 termed by M. De Blainville 

 vitrine auditive, from its 

 supposed analogy to the 

 vitreous humour of the eye. 

 It is similar in appearance 



Auditory Nerve. 



t0 the 



which 



1. Corpora quadrigemina. 2, 2. Processus 6 cerebello ad - . - - 

 testes. 3, 3. Corpora restiformia. 4. Fourth ventricle. 5. SUrrOUnuS it On the Outer 

 Iter a tertio ad quartum ventriculum. 6. Calamus scriptorius. -i 

 7. Posterior median columns of spinal cord forming by their 81(16, and intervenes De- 

 divergence the point of the calamus, also called ventricle of f-TTpppn it nnrl tViA QiflpQ rvf 

 Arantius. 8. Lines of origin of 4th ventricle, and of auditory L "tJtJll 11 dllU Lilt 

 nerve. 9. Anterior branch distributed to cochlea. 10. Poste- the OSSCOUS labvrinth SO aS 

 rior or vestibular branch. 11. Utriculus communis concealing w 

 sacculus proprius from view. 12. Ampulla of oblique semi- tO prevent any COtttaCt. 

 circular canal. 13. Ampullae of perpendicular and horizontal rpu f ^ *l 



semicircular canals. I he form of the mem- 



branous vestibule requires 



special notice, as it is not an exact imitation of the osseous cavity, 

 being composed of two distinct sacs which open into each other; one 

 of these is termed utricle, sinus seu alveus utriculosus, sacculus vesti- 

 buli, and median sinus; 



Fig. 72. the other, sacculus. Each 



sac contains in its interior 

 a small mass of white cal- 

 careous matter resembling 

 powdered chalk, which 

 seems to be suspended in 

 the fluid of the sacs, by 

 means of nervous filaments 

 proceeding from the audi- 

 tory nerves, G, N, Fig. 70. 

 From the universal pre- 

 sence of these substances 

 in the labyrinth of all the 

 mammalia, and from their 



Ampulla of the External Semicircular Membranous Canal, 



showing the mode of termination of its Nerve. 



much greater size and hard- 

 ness in aquatic animals, it is presumable, that they perform some office 

 of importance in audition. They are termed by M. Breschet, otolithes 



