134 ANIMAL BIOLOGY. [Part I. 



nearly horizontal in position, each of which, near the vestibule, 

 presents a bulging enlargement, the ampulla. The utriculus 

 gives off a diverticulum (di.). The sacculus contains a great 

 quantity of white crystalline calcareous otoliths. In the sacculus, 

 utriculus, and ampullae of the semicircular canals there are 

 special areas of ramification of the fibres of the auditory nerve. 

 In the sacculus and utriculus these take the form of thicken- 

 ings known as maculce acusticce, the similar thickenings in the 

 ampulla being known as cristce acusticce. The epithelium which 

 covers these is composed of columnar cells, between which are 

 wedged in spindle-shaped cells prolonged into auditory hairs. 



The auditory apparatus of the rabbit is more complicated. 

 The tympanic membrane does not lie on the surface, but at the 

 end of a short canal or external auditory meatus, the opening of 

 which is partially surrounded by the large pinna. Between the 

 tympanic membrane and the fenestra ovalis is a chain of three 

 small bones (see p. 146) which take the place of the columella 

 of the frog. The membranous labyrinth is enclosed in a bony 

 labyrinth, which consists of the densely ossified walls of the 

 chamber in which the membranous labyrinth lies, The sacculus 

 and utriculus are connected by a narrow channel from which the 

 recessus is given off. Connected with the utriculus are three 

 semicircular canals resembling those of the frog. But connected 

 with the sacculus is a new structure represented in the frog (if 

 at all) by the small dilatation already mentioned. This new 

 structure is the cochlear canal (c. c.) lying in the bony cochlea. 



The cochlea is like a snail-shell, with a central spindle, the 

 modiolus, around which winds a spiral canal with about two and ^ 

 a half turns. But the spiral canal is divided into three parts in 

 the manner shown in Fig. 43, B., which represents the cochlea 

 quite diagrammatically in cross section, c. c. is the cochlear 

 canal connected with the sacculus and containing endolymph : 

 s. v. is a second canal, the scala vestibuli, connected with the 

 bony vestibule in which the membranous vestibule lies, and con- 

 taining perilymph : s. t. is a third canal, the scala tympani, also 

 containing perilymph. The cochlear canal gets smaller as we 

 ascend the spire, which is supposed in the figure to be seen in 



