220 CLASS XV. 



Pipa, where bronchial rings exist. In the scaly reptiles, the 

 haplopnoa, the larynx, trachea and two bronchi are mostly dis- 

 tinguishable. The cartilaginous rings of the trachea are usually 

 complete circles and placed close together. In many serpents the 

 trachea is provided with rings at its lower part only, whilst the 

 anterior part expands into a thin cellular network. The bronchi 

 are in lizards usually very short, in the tortoises alone are they 

 longer, especially in the land-tortoises. The bronchus does not 

 usually divide in the lung, but ends suddenly or terminates in 

 a membranous band. In the crocodiles and tortoises the bron- 

 chus extends throughout the lung, and is perforated by many 

 openings, which lead into cells or sacs, whose walls are beset 

 with small cells. 



In the naked reptiles gills are present, either in their young 

 state, or, as in Proteus, during the whole of life, in the latter case 

 simultaneously with lungs, in the first before the lungs are de- 

 veloped. To the consideration of these gills we shall afterwards 

 revert in the systematic arrangement of this class. 



In vertebrate animals that breathe by lungs, the production of 

 sound is effected by an arrangement at the trachea, consisting of 

 elastic ligaments, which are caused to vibrate by the current of air. 

 In reptiles, birds and mammals, a voice can be produced by this 

 means, and the vocal ligaments, in the first mentioned, as in mam- 

 mals, are situated at the upper part of the trachea in an organ 

 named larynx. Many reptiles, however, emit no sound except 

 only a blowing, on the rapid expulsion of the air through the 

 glottis, as in the chameleon. Serpents give only a hissing sound 

 when disturbed. The glottis lies close behind the root of the 

 tongue, in serpents on the membranous sheath in which the tongue 

 at its hinder part is inclosed. The arytcenoid cartilages of batra- 

 chians are two triangular or oval parts, externally convex, internally 

 concave, and having a tense membrane at their inferior margin. 

 They form a dome-like eminence, on which, between the margins of 

 the cartilages, the opening of the glottis is situated 1 . The male of 

 many species of frog, as of Rana esculenta, have two vesicles under 

 the membrane of the tympanum, behind the angle of the mouth ; 



1 Comp. VICQ. D'AZYB, Mem. de VAcad. des Sc. 1779, Paris X 7 82 > PP- T 95> 

 PI. xm. figs. 4044. 



I 



