IV. VERTEBRATA: AMPHIBIA. 



583 



rzr 



very primitive, even the tympanum being absent, but in the Anura 

 a sound -conducting apparatus appears. 

 The spiracular cleft persists as a canal, 

 opening into the pharynx by the Eu- 

 stachian tube, its outer end expanded into 

 the tympanic cavity and closed externally 

 by the tympanic membrane, supported by 

 the cartilaginous tympanic annulus (dot- 

 ted circle in fig. 612, B). The connexion 

 of the labyrinth with the tympanum is 

 by an opening in the otic capsule, the 

 fenestra ovalis, in which is the stapes 

 (? part of capsule), the columella extend- 

 ing from this to the tympanic membrane 

 and carrying the sound waves across to 

 the inner ear. The brain (fig. 614) has 

 advanced above that of the fishes in the 

 stronger development of the cerebrum, 

 but remains behind in the small size of the 

 cerebellum, which is but a thin lamella. 



The respiratory organs afford impor- FIG. 6U.-Brain of frog. /, line 



i , -i .-11 j - between olfactory lobes and 



tant characters, Since both gills and lungs cerebrum; Frh, fossa rhom- 



occur. Of gills there are two kinds, inter- ifStoryve-! 



ZH ' ' twixt brain - 



nal (found only in Anura), of entodermal 

 origin, and ectodermal gills, external in 

 position (figs. 4, 5), occurring in all. These ectodermal gills, three 

 in number, are richly vascular and arise from the skin at the 

 upper part of the gill clefts. The paired lungs open into the 

 hinder part of the pharynx, either directly through the glottis or 

 more rarely by a short trachea. Cartilages, the remnants of gill 

 arches, may support trachea and glottis, and on the latter support 

 vocal cords (larynx). Breathing is accomplished by a kind of 

 swallowing, the air being forced into the lungs by the muscles of 

 the floor of the mouth and the pharynx. Persistent gills and 

 lungs are found only in the Perennibranchs. Usually the young 

 breathe by gills, the adults by lungs, the origin of the metamor- 

 phosis to be described below. 



Besides gills and lungs the skin is an important respiratory 

 organ, as are pharynx and mouth cavity, in which the air must re- 

 main for some time on account of the respiratory mechanism. This 

 renders intelligible the fact that many Salamandrina (Spelerpes, 

 DesmognatJius, Pletlwdon, Gyrinophilus, etc.) have neither gills 



