250 



ELEMENTS OF MAMMALIAN ANATOMY 



(Fig. 1 20). Its outer or lateral third is formed by cartilage, 

 and the remainder by the tympanic portion of the temporal 

 bone (Fig. 18). The meatus is lined with mucous membrane 

 in which are numerous sebaceous and oleaginous glands. The 

 latter secrete the wax of the ear. 



The middle car, or tympanum, is an irregular cavity about 

 one centimeter in diameter contained in the lateral chamber 

 of the bulla (Fig. 120). It is separated from the external 

 auditory meatus by the delicate translucent membrane, the 

 membra na tympani. The petrous bone containing the internal 



ear forms part of the inner or 

 medial wall. In the petrous 

 bone are two foramina which 

 may be seen in a dry skull by 

 looking through the external 

 auditory meatus. The more 

 dorsal foramen is the fenestra 

 vestibuli, which in the recent 

 state is closed by a membrane 



The internal ear is represented re- ^ • i i r . r j.i 



moved about a centimeter from the tO whlch the foot of the StapCS 



middle ear and slightly rotated to the -g attached. The ventral one 



left. The base of the stapes, s, m 



nature, covers the fenestra vestibuli, is the fenestra COcklcOS, also 



ov, c, basal whorl of the cochlea: ea, i i i v • i.T_ 



external auditory meatus; eu, open- cloScd by a membrane m the 



ing of the Eustachian or auditory reccut State. In the dry skull 



tube; i, incus; in, malleus; sc, semi- m t 



circular canals; ve, vestibule; /, the fenestra VCStlbull OpenS mto 



tympanum. ^^^ ^^^^ ^^ ^^^^^ ^^^^-y ^f ^j^^ 



cochlea, and the fenestra coch- 

 leae opens into the vestibule of the internal ear. The auditory 

 tube (Fig. 19), whose opening may be seen craniad of the 

 tympanic bulla, connects the middle ear with the posterior 

 nares and thus admits air to the tympanic cavity. 



To demonstrate further the anatomy of the middle ear, one 

 should clean the flesh from a fresh or preserved head and care- 

 fully cut away the ventral walls of both chambers of the tym- 

 panic bulla (Fig. 18). 



Fig 



120. — Diagram of the Mam- 

 malian Ear. 



