34 ELEMENTARY BIOLOGY. [CHAP. 



and contained, as has been stated, in the periotic capsule 

 into which it fits but loosely; the interval between the two 

 being filled with a fluid, the perilymph. In the outer face 

 of the periotic capsule is an opening, the fenestra ovalis, into 

 which the end of the columella auris fits. This columella is 

 shaped like a pestle, the end of the handle of which is fitted 

 with a cross-piece. The rounded inner end of the pestle, 

 which is fixed by fibrous tissue into the fenestra ovalis, is 

 cartilaginous. The middle of the handle is ensheathed in 

 bone, while the outer part is cartilaginous. The cross-piece 

 is fixed into the inner face of the membrana tympani, which 

 is covered externally by the integument, and lined internally 

 by the mucous membrane of the tympanic cavity, which is 

 continuous with that of the mouth through the Eustachian 

 recess, and wraps round the ventral face of the columella. 

 A sound wave, impinging upon the drum of the ear, is trans- 

 mitted through the agency of the columella to the perilymph 

 and endolymph, auditory epithelium and nerve, to the brain. 



The Tongue. This organ, as has been seen, is fixed only 

 in front to the mandible, and by the anterior half of its ven- 

 tral aspect to the floor of the mouth; the posterior half 

 being free and bifid at the extremity. Narrow-ended and 

 broad-ended papillae (papilla filiformes and fungiformes) are 

 scattered over the whole dorsal aspect of the tongue and are 

 largest in front ; small glands lie between these papillae. 



The fungiform papillae contain the ultimate ramifications 

 of the glossopharyngeal nerve, and the epithelium covering 

 their summits is peculiarly modified. 



The Integument. No special organs of touch have been 

 observed, but the integument is remarkable for the immense 

 number of close-set simple glandular caeca (cutaneous glands) 

 which open upon its surface. In the swollen integument 



