Mouth and Tongue of the Frog. 



39 



teeth are not joined together like those of the maxillaries, but 

 are fixed separately to the membrane beneath. It is easy to 

 perceive by the manner in which this sphincter oris acts, that 

 by their ras})iug action these teeth must materially assist the 

 maxQlary organs in the comminution of food*. 



The papilhe are generally of a conical shape ; those situated 

 among the folds ai-e simple cones fixed to the membrane, and 

 about j^o'^tli of an inch in height ; others at the angles of the 

 lips are compound, consisting of an agglomeration of simple 

 papillEe disposed around a common stem. The exterior of each 

 papilla is formed of a zone of ciliated, globular or prismatic cells. 



The interior of the papilla presents numerous transverse lines, 

 apparently constituting septa, dividing the part into compart- 

 ments or cells. The cellulated part is generally limited at the 

 summit of the cone by the external zone of epithelium; but in 

 some cases the cone is truncated, and the cellulated portion 

 forms the summit. Each papilla receives a looped capillary, 

 which generally ascends to about two-thirds of the height of the 



Figl. 



Magnified 200 diaraetera. 



cone. (See fig. l.j 



The nerse-tubes which supply these 

 bodies are large, well-defined, and 

 with the double contour indicating 

 tlie existence of a vigorous and perfect 

 nervous action. In most cases not 

 more than a single tube can be found 

 running to each papilla. Then- mode 

 of termination is apparently in free 

 extremities ; but, unlike the nerves of 

 the fungiform papilla of the frog, 

 their point of termination usually 

 falls off in a veiy gradual man- 

 ner. 



The labial folds (like the branchia), 

 with their teeth and papillfe, are cast 

 off as the animals attain their full de- 

 velopment or frog state. About the „... 



period of the appearance of the hind-limbs we first observe signs 

 of alteration in these organs. The gradual steps by which this 

 transformation of the buccal orifice and cavity takes place are 

 generally witnessed in the shedding of some of the teeth, the 

 atrophy of the papilla;, and the disappearance of the folds about 



* The tadpole in its early stages is well-adapted for observing the heart's 

 action, as tlie intes^niuu-nts are sufficiently transparent to allow the move- 

 ments to be studied with a low microscopic power. For this purpose it i« 

 merely necessary to place the animal on its back in a shallow cell with 

 water, covered at the top to prevent it from turning over. 



Labial payjiUae of the tadpole. 

 AA. Zone of epithelium. 

 CC. Cupillary. 

 N. Nerve. 



