XIII.] THE FROG. 187 



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 (papillae filiformes and fungiformes) are scat- 

 tered over the whole dorsal aspect of the tongue and are 

 largest in front ; small glands lie between these papillae. 



The fungiform papilla 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 interposed glands are 

 developed. 



A singular body of unknown function, the Irowspot or 

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

 cells, occurs in the integument of the frontal region of the 

 head. 



Cells containing pigment abound in the integument and 

 undergo remarkable changes of form, the pigment being 

 sometimes drawn together into a spheroidal mass at other 

 times distributed in a radiating fashion. 



