II SKIN 31 



Cranial dermal ossifications are developed in some species of 

 Bitfo, still more in the Hemiphractinae, and above all in I'dit- 

 hates cuItri^Ji's and in the Cystignathoid genus ('(ili/jifiinphirlua. 



The hyoid apparatus of the Auura is complicated. It is 

 originally composed of the hyoidean and four branchial arches, 

 with one median, copular piece. The branchial arches form in 

 the early life of the tadpole the elaborate framework of the 

 filtering apparatus mentioned on p. 44. During metamorphosis 

 the whole filter disappears, owing to resorption of the greater 

 part of the branchial arches ; only their median portions remain, 

 and fuse with the enlarged copular piece and the hyoidean 

 arches into a broad shield-shaped cartilage (corjms linyuae), 

 whence several lateral processes sprout out, the posterior pair of 

 which are generally called thyrohyals or thyroid horns. The 

 true hyoid horns give up their larval lean-to articulation with 

 the quadrate, become greatly elongated, and gain a new attach- 

 ment on the otic region of the craniimi. The transformation of 

 the whole apparatus has been studied minutely by Eidewood, in 

 Pehdytes jnmctatus? 



Skin 



The epidermis of the young larvae of Amphibia is furnished 

 with cilia, which later on are suppressed by the development of 

 a thin hyaline layer or cuticula, but clusters of such cilia 

 remain, at least during the larval life and during the periodical 

 aquatic life of the adult, in the epidermal sense-organs. In the 

 frog, currents are set up by the ciliary action at an earliei- stage, 

 and are maintained to a later stage than in tire newt. In the 

 latter the tail loses its ciliation, whereas in the frog it remains 

 active almost up to the time of the metamorphosis. In tadpoles 

 of 3-10 mm. nearly the whole surface is ciliated (Assheton).- 

 The cilia work from head to tail, causing the little animal, when 

 perfectly quiet, to move forwards slowly in the water. Beneath 

 the cuticula, in the Perennibranchiata and the larvae of the 

 other Urodela, lies a somewhat thicker layer of A-ertically striated 

 cells, the so-called pseudo-cuticula, which disappears with the 

 transformation of the upper layers of the Malpighian cells into 

 the stratum corneum. The latter is very thin, consists of one or 

 two layers of flattened cells, and is shed periodically by all 

 1 P.Z.S. 1897, p. 577. ^ Q.J..V.S. xxxvjii. 1896, p. 465. 



