Organ of Hearing. 145 



(Semiplantigrada, Lutra) of the Sectorialia the Malleus is perforated 

 near the origin of the process. 



4. Stapes and Incus. 



Terf oration transversed hy osseous cylinder. 



In most Insectivora {e.g. Mole) part of the osseous wall of the 

 labyrinth conducts a vessel and nerve through the opening of the 

 Stapes. 



This is also the case in many Rodentia {e.g. Squirrels, Cavies, 

 Marmots). 



Avian type. 



In some Bats (Cheiroptera), e.g. Vespertilio noctula, maybe noted 

 a retention of the columelliform confluence of Stapes and Incus. 



In most Marsupialia {e. g. in Perameles), and Monotremata, the 

 Stapes is columelliform ; its base oval, supported on an imperforate 

 stem ; its apex being more expanded in the former than in the latter 

 Order. 



Stapes imperforate. 



In addition to the above-named instances ; note this also in the 

 Walrus (Sect. Pin.) and Delphinus leucas (Cete). 



5. Semicircular Canals. 



In most Insectivora the bony semicircular canals project from the 

 petrosal capsule within the cranium, and conspicuously so in the 

 Mole (Talpa), in which the petrosal is large and cellular. 



All insectivorous Cheiroptera and Monotremata likewise show this 

 same projection. 



6. Vestibule, &c. ' 



In the Whales the Vestibule of the labyrinth is all but wanting. 

 In the Sloths there are only two * ampullae,' none being met with 

 upon the external canal. 



7. Cochlea, &c. 



In the Monotremata the Cochlea has only a half coil ; 

 in Bimana, Quadrumana, Cheiroptera, SoUdungula (Perrisso-d.), 

 and Rumiiiantia (Artio-d.), two and a half qotI^ ; 

 in Sectorialia three coils ; 

 in most Rodentia four ; in Caelogenys Paca nearly ^t^e coils. 



