i yo 



THE SKULL. 



[CHAP. 



inner side of the centre. The lower lip of the external 

 auditory meatus is extremely short ; the meatus , in fact, 

 looks like a large hole opening directly into the side of the 

 bulla, On looking into this hole, at a very short distance 

 (just beyond the tympanic ring), a wall of bone is seen quite 

 impeding the view, or the passage of any instrument, into" 

 the greater part of the bulla. In the section (Fig. 57) it will 

 be seen that this wall is a septum (s\ which rises from the 



00 



FIG. 57. Section of the left auditory bulla of the Tiger (Fells tigris). Sq squa- 

 mosal ; Pt periotic ; BO basioccipital ; am external auditory meatus ; oc the outer 

 chamber ; ic the inner chamber ; j the septum ; * the aperture of communication 

 between the chambers. (From Proc. Zool. Soc. 1869.) 



floor of the bulla along its outer side, and divides it almost 

 completely into two distinct chambers ; one (pc), outer and 

 anterior, is the true tympanic chamber, and contains the 

 tympanic membrane and ossicula, and has at its anterior 

 extremity the opening of the Eustachian tube (e) ; while the 

 other (ic), internal and posterior, is a simple but much 

 larger cavity, having no aperture except a long but very 

 narrow fissure (*) left between the hinder part of the top of 



