336 



METAZOAN PHYLA 



sensation which is called smell. Small particles entering the mouth 

 through the air and being dissolved in the saliva or entering it in solution 

 can affect in a similar way groups of cells known as taste huds (Fig. 233) 

 on the surface of the tongue, soft palate, or pharynx and cause a sensation 

 which is recognized as taste. From what has been said it is evident that 

 the senses of smell and taste are allied and that one may both smell and 

 taste a substance at the same time. In some aquatic animals taste buds 

 also occur on the outer surface of the head and especially on the soft 

 barbels of such fish as the catfish and bullhead. 



Pinna 



Malleus 



Stapes closing 

 fenestra o^al/s 



Incus \ Semicircular 



''>^l \ Utriculusyfcarna/s 



'■ "t— ^-._ ^/. Auditory 



Ampullae \nerve 



■Endolyrnphatic 



External 

 auditory 

 meatus 



m 



«' Tympanic 

 tnembrane 



'embram 

 closing fensi ^ 

 f\a rotunda 

 Tympanum 



Sacculus 



Xochlea 

 Eustachian tube 



Fig. 234. — Diagrammatic section of the human ear. Cavities unshaded. The cochlea 

 is shown made up of three coils, each divided by a continuous membrane which is not 

 continued to the tip. In this way the cavity of the cochlea is divided into two parts, the 

 scala vestibuli, which opens into the sacculus, and the scala tympani, the end of which is 

 shut off from the tympanum by a membrane closing the fenestra rotunda, also called 

 fenestra cochlearis. The two scalae communicate at the tip of the cochlea. 



354. Ear. — The ear of vertebrates may consist of three parts (Fig. 

 234). These are the inner ear, which is present in all forms and which 

 contains the essential organs of hearing and equilibrium; the middle ear, 

 which is found only in the Amphibia and in higher classes of vertebrates; 

 and the outer ear, which is confined to the reptiles, birds, and mammals. 

 The outer ear is well developed only in the mammals, in which is usually 

 added a broadly expanded 'pinna — the visible part and that ordinarily 

 called the ear. The human ear, as an example of the most highly devel- 

 oped auditory organ, will be described. 



The inner ear is inclosed in the temporal bone, which forms a part of 

 the side wall of the cranium. It consists of cavities and canals, sur- 

 rounded by a fibrous membrane, which together form the memhranous 

 labyrinth. These in turn are fitted into a system of bony spaces forming 

 the bony labyrinth. Lymph fills the membranous labyrinth and occupies 

 the space between it and the bony labyrinth. The membranous labyrinth 



