256 



ANIMAL PHYSIOLOGY. 



walls, which belong to the temporal bone. The integument 

 with which it is lined secretes cerumen from glands of a 

 structure similar to sweat glands, and is furnished, towards 

 the superficial extremity, with fine hairs inclined outwards, 

 so as to offer an obstacle to the entrance of particles of dust. 

 Additional protection is given by the direction of the canal, 

 which is inclined slightly backwards at its commencement, 

 under cover of the tragus, then turns a little forwards; and 

 also in the outer half has an upward slope, which is suddenly 

 changed for a downward inclination in the deep part. 



Fig. 127. DIAGRAM OP THE RIGHT EAR. a, Osseous part of the 

 canal of the external ear; b, membrana tympani with the upper 

 part removed; c, malleus; d, incus; e, stapes with its base filling 

 up the f enestra ovalis (the f enestra rotunda is seen a little lower) ; 

 /, Eustachian tube; g, tensor tympani muscle; h, stapedius 

 muscle; i t i, portio dura of the seventh nerre divided; 1c, mastoid 

 cells; Z, m, vestibular and cochlear divisions of the portio mollis 

 or auditory nerve; n, vestibule; o, cochlea. 



The membrana tympani blocks up the inner end of the 

 canal. It consists of a fibrous membrane with a thin cover- 

 ing of integument on the outside, and of mucous membrane 



