Studies on Amphibian Metamorphosis Xv. Direct Tympanic Membrane Formation from Dermal Plicae Integument Transplanted to the Ear Region

THE dermal plicae folds or ridges of the metamorphosed anuran constitute striking integumentary structures. In most anurans two sets of dermal plicae are present, viz. a dorso-lateral set which run posterior from the dorso-posterior border of each eye to a point just lateral to the urostyle prominence, and a lateral pair originating near the external nares of either side and thence running posterior along the upper jaw ventral to the tympanic membrane to a point just dorsal to the base of the fore limb. The folds, as the term indicates, appear externally as definite elevated ridges of which the dorsal-lateral pair are usually the more prominent. They are more often dull white in appearance although frequently of a somewhat greyish tinge, the latter condition being more typical of the lateral than of the dorso-lateral pair. Histologically, the folds are seen to be due chiefly to much enlarged mucous and poison glands, usually closely approximating one another. This necessarily requires a corresponding thickening of the stratum spongiosum of the integument, in which layer the glands are located. In addition, the stratum compactum is also considerably hypertrophied, while the epidermis usually contains more cell layers as compared with that of ordinary back integument.