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AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



(2) Gustatory Organs. Imbedded in the sides of the circum- 

 vallate papillae and papillae foliatae are numerous taste-buds, con- 

 taining elongated taste-cells, connected with glossopharyngeal 

 fibres. 



(3) Olfactory Organs. The nasal cavities (Fig. 85) are largely 

 lined by olfactory mucous membrane, which extends over the ethmo- 

 turbinals, and contains elongated olfactory cells (cf. Fig. 62). 



(4) Auditory Organs. (a) The external ear consists of a pinna 

 and an external auditory meatus, closed below by the tympanic 

 membrane. This last also forms the upper and outer boundary 

 of (6) the middle ear or tympanic cavity, which has already been 

 described, (c) The inner ear (Fig. 91,0) is, broadly speaking, 



Fig. 91. DIAGRAMS or THE MEMBRANOUS LABYRINTH (from Haddon). 

 Internal side of left labyrinth. A, Fish, B, Bird. C. Mammal ; us, 

 utriculus and sacculus ; u, utriculus ; s, sacculus ; c, cochlea. 



similar to that of the pigeon, but the semicircular canals are ar- 

 ranged rather differently (the anterior vertical not crossing over 

 the horizontal), the sacculus and utriculus do not communicate 

 directly, and the cochlea is produced into a delicate tube, spirally 

 coiled, and contained within the promontory. A special series of 

 special sense cells (hair-cells) are formed in the cochlea. This 

 also contains a large number of pairs of elastic fibres, of different 

 lengths, constituting the problematical organ of Corti and forming 

 a series of /y-shaped arches projecting into the endolymph. 



(5) Visual Organs see Figs, 63 and 64). The eye and the 



