xiii.J THE FROG. 195 



opening, the fenestra ovalis, into which the end of the 

 vlumella 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 lined externally by 

 the integument, internally by mucous membrane, continuous 

 with that of the mouth through the Eustachian recess. 

 The mucous membrane of the tympanic cavity covers 

 only the ventral face of the columella, over the dorsal face 

 of which the posterior division of the facial nerve passes. 



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 which open upon 

 its surface. In the swollen integument which covers the 

 base of the inner digit in the males, large papillae with inter- 

 posed glands are developed. 



A singular body of unknown function, the browspot or 

 inter-ocular gland, consisting of a spheroidal sac with minute 



132 



