220 



MAMMALIAN ANATOMY 



The anterior wall (Fig. 148) faces backward and to a slight degree 

 outward, and is strongly concave from above downward and from side 

 to side. It passes below into the lower wall, or, rather, into the groove 

 formed by the meeting of the outer and the inner wall. It forms a 

 decided angle with the upper wall. The anterior wall is an oblong 

 strip passing from above downward and inward ; above and within 

 are seen the slit-like opening of the Eustachian canal and the Glaserian 

 fissure, and on the outer side the ectotympanic hook and the opening 

 of the canal of Huguier. On the inner wall of the Eustachian canal 

 is the minute foramen for the carotid artery. 



FIG. 150. 



Superior Process 

 of Incus. 



Base of Stapes. 



Bridge. . . 



Aquxductus 

 Fallopii. 



Tympanum. 



Entotyrnpanie, 



Cavity. 



Head of Malleus. 



Neck of Malleus. 



Ectotympanic 



Hook. 



External Auditory 

 Meatus. 



Handle of Malleus. 



Bullar Septum. 



LEFT EAR OSSICLES IN POSITION. (PETROUS REMOVED.) SUPERIOR MEDIAL ASPECT. 



(Enlarged Four Times.) 



The posterior wall of the tympanum (Fig. 149) has the same 

 general outline as the anterior wall. To the outer side of the middle 

 is seen the crescentic opening into the inner chamber over the septum 

 of the bulla. Below this opening the edge of the septum passes 

 upward and outward to join the rim of the auditory meatus. A little 

 within this point of junction is the opening for the chorda tympaui. 

 Above this opening is a fossa bounded on the outside by the squamous 



