ORGAN OF HEARING IN MAMMALIA. 339 



wide apart, and the articular one is the longest. The ear-conchs 

 are large, delicate ; in some genera of Bats enormously expanded : 

 they have been noticed, together with their vibratory movements, 

 under the f Organ of Touch.' In the frugivorous kinds the conch 

 is small ; but with tragus and antitragus very distinct. A large 

 and expanded malleus obtains in Pteropus fuscus, with the 

 process and handle of almost equal length. The stapes is narrower 

 in proportion to its length than in true Bats. 



In most Insectivora the bony semicircular canals project from 

 the petrosal capsule within the cranium, and conspicuously so in 

 the mole, in which the petrosal is large and cellular. Part of 

 the osseous wall of the labyrinth conducts a vessel and nerve 

 through the opening of the stapes, as shown in fig. 173, c. The 



173 



Stapes in Lissenccphala. 

 a. Bat. b. Shrew. c. Mole. D. Hedgehog. e. Marmot. f. Sloth. 



base of this ossicle is very thin at the middle ; it has a wide 

 opening : the malleus has an elongate tuberous head. The ear- 

 conch does not project. In Shrews it is generally broad, thin, 

 naked, and complex, rounded, and but little projecting. In Sorex 

 fodiens, Pall., the free margin is folded and concealed by the sur- 

 rounding hair: in the Water- Shrews the protecting hairs are 

 longer ; there are two folds within the conch ; the upper one has a 

 marginal row of hairs ; the lower one — a kind of antitragus — can 

 be folded over the auditory canal. When the outer margin of 

 the conch is unfolded it reaches to the level of the top of the 

 head. In the great groove-toothed shrew (Solenodon) the auricle 

 is shaped as above, has the free margin unfolded, has fine short 

 hairs on both surfaces ; and the protecting folds of the meatus at 

 the bottom of the conch are relatively small, but complex. 



The lamelliform type of malleus prevails in all Shrews : it is 

 figured from Sorex araneus, in fig. 173, B, a, d. In the Hedgehog 

 the oval and round apertures of the labyrinth are approximate : 

 the cochlea makes a slight projection into the tympanic cavity. 

 The basisphenoid enters, as in Marsupials, into the formation 

 of the tympanic cavity, and the tympanic bone retains its free- 

 dom and is almost restricted to the support of the drum-mem- 

 brane: the stapes, fig. 173, d, has slender, uneq.ua! crura, and 



