526 



iESTHESIOLOGY. 



extends from the base of the concha to the tympanic membrane 

 bounding the cavity. It is partly osseous 

 and partly cartilaginous, and is narrower in 

 the middle than at either extremity. Jts 

 lining is a continuation of the skin of the 

 concha, and it graduaUy becomes thinner as 

 it descends ; it is perforated by numerouii 

 small openings from the ceruminous glands, 

 which secrete the wax of the ear. The 

 cartilages of the external ear are the conchal, 

 the annulcir, and the acwtifoimi. 



The conchal cartilage has some cnaracter- 

 istic feature, in shape or size, in most classes 

 of animals ; in the horse it is a conical tube, 

 with the narrow end downwards, and having a 

 perpendicular aperture directed forwards when 

 the ear is ' ' set ; " it terminates superiorly in 

 a point on the posterior border. Inferiorly 

 it is attached to the annular or ring-shaped 

 cartilage, which surrounds and is attached to 

 the bony meatus. The scutiform cartilage is 

 an irregularly triangular plate, partly covering 

 the temporalis muscle, and attached by muscles 

 to the conchal cartilage and to the 

 bones of the skull ; it appears to act 

 as a kind of lever in moving the 

 concha, the mobility of which struc- 

 jFiG. 198. ture is so great in the solipede, that 



JCrilSriu?,,^:;^ J' i= «g^«J. "<>« mappropriately, 



^ anterior angle ; d, Supero-posterior aS the chief OTQOiTi of eXJOTCSStOTh in 

 'angle; e, Anterior border; /, Poste- +1, f '1 

 rior border ; 3, Snperkurborder. tliat animaL 



Fio. 197. 



Eight conchal and an- 

 Bular cartilages. 1, Con- 

 chal cartilage; a.Sttperior 

 extremity ; 6, Inferior 

 extremity ; c, Outer sur- 

 face ; d, Inner surface : 

 e. External border; /, In- 

 ternal border; 2, Annu- 

 lar cartilage ; g, Anterior 

 surface ; h, Superior; and 

 i, Inferior border. 



MIDDLE EAR. 



The middle ear or tympanum is an irregular bony cavity within 

 the petrosal bone. It is bounded externally by the membrana 



rpani or drum of the ear ; internally by the bony walls of 

 internal ear ; anteriorly by the Eustachian tube ; and pos- 

 teriorly by the mastoid cells. 



The Membrana tympant is a semi-transparent, nearly circular 

 membrane, vsdth its middle drawn inwards. It is inserted to a 



