ORGANS OF RESPIRATION*. 553 



of salamandra and of the anurous amphibia. These organs 

 are much more developed in the adult frogs, toads, and sala- 

 manders, where the lungs are capacious, broad, short, entirely 

 subdivided internally into large cells, and more confined to 

 the anterior portion of the trunk. 



Along the sides of the short membranous trachea, both of 

 the caducibranchiate and perennibranchiate amphibia, irregu- 

 lar longitudinal continuous tracheo-laryngeal patches of carti- 

 lage are seen extending, and these shoot out transversely 

 small processes, which in higher animals become, by absorp- 

 tion, distinct isolated tracheal rings. The upper portion of 

 these two lateral tracheo-laryngeal cartilages already become 

 separated to form arytaenoid cartilages in all the amphibia, 

 as shown by Henle, and the rudiments of cricoid and thyroid 

 cartilages are generally perceptible, thus composing a rudi- 

 mentary larynx or organ of voice ; the lower portions, descend- 

 ing along the lower sides of the trachea, become broad, and 

 their lateral processes almost divided into distinct transverse 

 pieces, the rudiments of tracheal rings, in the salamanders, and 

 they are more distinct in the pipa and in the ctecilia. In the 

 frog, the small cornicula laryngis are already detached from the 

 ends of the arytaenoid cartilages, as in mammalia. 



The larvae of frogs and other caducibranchia, breathe for a 

 time, both by lungs and branchiae, and by the naked surface of 

 the skin, as the perennibranchia ; the branchiae of the frog are 

 early withdrawn into a capacious pharyngeal cavity, commu- 

 nicating externally, as in cartilaginous fishes, by small lateral 

 cervical openings, which soon close up entirely, and the 

 cavity remains capacious in the male, for the production of 

 the croaking sounds. As the ribs, when present, are ineffec- 

 tive for respiration in amphibia, the lungs are gradually filled 

 with air by the successive movements of the os hyoides and 

 pharynx, as in chelonian reptiles where the ribs are entirely 

 immoveable, hence they are unable to breathe when the 

 mouth is forcibly kept open. The higher amphibia thus 

 exhibit remarkable metamorphoses in their respiratory organs, 

 commencing their career while yet in the ovum, with cuta- 

 neous vibratile cilia, like the respiratory organs of the lowest 

 radiated animals, then acquiring external branchial tufts like 

 those of the lowest worms or gasteropods, then internal 

 covered branchial laminae like those of fishes, and at length 

 internal cellular lungs like those of the higher vertebrata. 



