AMPHIBIA. 401 



(Siren) or fenestrate (Proteus, Menobranchus] cartilage tube : they open 

 internally within the lip in front of the ethmopalatine, there being no 

 maxillae. The mucous membrane, as in Fish, is disposed in radial folds. 

 In other Amphibia there are as a rule cartilaginous turbinal ridges, and the 

 internal nares lie between the maxillae and vomers. The Urodela possess 

 an internasal gland opening into the mouth and lodged in the septum of 

 the nose. It lies more anteriorly under the praemaxillae in Anura. Other 

 glands open into the narial chambers, and in Anura on the oral mucous 

 membrane as well. In the Gymnophiona the cartilaginous ridges are re- 

 placed by bony ridges developed on the bones surrounding the narial 

 chamber. The tentacles are structures peculiar to this group. They are 

 essentially fibrous sacs lying in the cavity of the orbit, and opening 

 anteriorly in front of it. They contain large glands and a retractor muscle, 

 which is attached anteriorly close to the external aperture. At this spot 

 there is a ridge or papilla which can be protruded and retracted. A gland 

 lying in the nasal cavity opens into the sac near its external aperture. The 

 eye is small in comparison with that of Fish, but as in that class, the lens is 

 spheroidal, and the cornea, except in the Land Salamander (5. terrestris), 

 flat. The eye is hidden beneath the integument in Proteus and Gymno- 

 phiona. An upper and lower lid is usually developed in Urodela : the latter 

 in Anura forms a large nictitating membrane, connected at its angles with 

 the retractor bulbi muscle. The lacrymal gland is absent, but there is a 

 Harderian gland in Anura. A lacrymal duct leads to the narial chamber, 

 except in Gymnophiona. The ciliary muscle is feebly indicated. Colourless 

 or faintly yellow oil globules are found in the cones si Anura. There is no 

 tympanic cavity in Urodela, and the same is true of some Anura, but a 

 simple stapes is present, attached to the membrane of the fenestra ovalis. 

 Other Anura have a tympanic membrane attached to a tympanic annulus, 

 the homologue of the spiracular cartilage of Elasmobranchii, a tympanic 

 cavity, and a well-formed and complex stapes or columella auris (supra, p. 

 339), and a fenestra rotunda in addition to the f. ovalis. In the aglossal 

 Anura (Pipa, Dactylethrd} the two Eustachian tubes have a single median 

 pharyngeal orifice. The semicircular canals are well curved in Amir a, 

 flattish in Urodela. The sacculus is large in Urodela, but becomes reduced 

 with the increase in the size of the cochlea in Anura. The internal ear is 

 very rudimentary in Siphonops annulatus, and probably in all other Gymno- 

 phiona, and contains no sensory nerve-endings. 



Amphibia are sometimes edentulous, e. g. Pipa and the Bufonidae. The 

 Tadpole of the Anura has the jaws covered by a horny sheath. The same 

 is the case with the praemaxillae and dentary bones of Siren lacertina with 

 the addition, however, of true teeth on the vomero-palatines and splenials. 

 The adult Anura rarely have teeth on the dentaries, and those structures 

 are confined in them to the praemaxillae, maxillae and vomers. On the 



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