Clasa 3. , Amphibia. 399- 



which, dovetail with those of adjacent arches. In the larval Anura 

 with internal gills, this straining apparatus reaches a high pitch 

 of perfection, so that it is able to exclude even the very finest 

 particles from the branchial-cavity and the delicate membranous 

 gill-tufts within it. For the branchial vessels, see below. 



The lungs, occurring in all Amphibia, are two saccular organs, 

 which in some forms {e.g., Newts, Proteus) are quite simple, in 

 others (Salamanders, Anura), are provided with short, thick-set 

 evaginations (Pig. 845 £) . In the Grymnophiona, the right lung is 

 much shorter than the left. The trachea, which is almost always 

 very short, opens by a longitudinal slit into the back of the mouth ; it 

 is supported by several cartilages, and in the Anura, contains vocal 

 cords, which are absent from all the others. To effect an inspira- 

 tion, the animal depresses the soft parts between the rami of the lower 

 jaw, by shutting the mouth, and draws air into the buccal-cavity 

 through the open nares ; these are now closed and the lower wall of 

 the buccal-cavity is raised, so that the air is forced into the trachea; 

 it is forced out by the contraction of the body-wall and its pressure- 

 upon the elastic lungs. 



In some Salamanders, e.g., two species in S. Eiirope, the Ituigs are rudimentary 

 or entirely absent. Respiration is effected hj means of the skin (of great import- 

 ance in this connection in all AmpMMa) and the huccal cavity, where inspiration 

 and expiration proceed in the usual way. 



The vocal cords of the Anura are made to vibrate by the expired air, and thus 

 sounds are produced. In the males of many species, this noise may be intensified 

 by means of evaginations of the posterior region of the buccal-cavity, which can 

 be blown out at pleasure into thin-walled sacs of considerable size. A pair of 

 such resonators is present ; in some (e.g., the Tree Frog), they unite to form a 

 single unpaired vesicle, which is, however, connected with the mouth by two 

 openings. The Urodela can produce sounds, although they have no vocal cords. 

 The heart (Pig. 284) differs from that of most Pish in that the 

 atrium is divided by a septum into two auricles, right and left j 

 the latter is the smaller, and receives blood from the lungs, whilst 

 the right receives blood from the rest of the body. The septum is 

 often pierced by larger or smaller apertures, and is thus imperfect. 

 The ventricle is undivided, and shows no trace of separation ; 

 as in Pish, its wall is thick and spongy, the small spaces open- 

 ing into the central cavity ; the auriculo-ventricular apertures are 

 guarded by valves. The conns arteriosus, which arises in 

 front from the right side of the ventricle, is usually a well-developed 

 tube, somewhat spirally curved. It displays at each end a trans- 

 verse row of valves, and is in addition provided with a longi- 

 tudinal fold, which is connected with a valve of the anterior 

 row, and projects into the cavity of the conus (for its significance 

 see below). 



The arterial system in amphibian, larv^ is piscine in char- 

 acter : an afferent branchial artery, arising from a very short ventral 

 aorta, runs to, an efferent artery runs from, each gill-bearing gill- 



