OEGANS OF RESPIRATION AND VOICE. 171 



pecially in the Chameleon, hollow ccecal diverticula are given off from 

 the lungs. 



The internal structure of the lungs differs in the several 

 orders and genera of Reptiles, the respiratory surface being very 

 much increased in the Squamigera by the development internally 

 of cells, while in the lowest orders, the lungs are simply hollow bags. 

 In the Ichthyodea and Tailed Batrachia their condition is of the sim- 

 plest kind, as in Proteus and Triton, where they form, as already 

 stated, simple bladder-like sacs, directly continued from the mem- 

 branous larynx. In the Salamander the lungs begin to assume an 

 uneven appearance from the occurrence of small inversions. In the 

 Anourous Batrachia their respiratory surface is increased by mem- 

 branous cells which project into them internally, and form with the 

 lateral walls open rhomboidal, or more or less hexagonal or polyhe- 

 dric spaces, upon which lesser cells again rest, these last opening 

 in the inward direction into the common cavity of the lung. The 

 lungs are more perfectly formed in the Chelonia and Sauria, although 

 several genera of the latter frequently retain the simple character 

 of membranous sacs, with an areolar tissue developed upon the in- 

 ternal surface of their walls, but no internal dissepiments. In both 

 orders the cartilaginous rings of the bronchi becoming more imper- 

 fect are continued as strips, which, cartilaginous at first, are next 

 converted into tendon, and form rounded or angular meshes which 

 rest partly upon the walls of the lung, and enclose lesser meshes or 

 air-cells, or are united together internally so as to form numerous 

 dissepiments ; thus the whole lung is filled more or less by a coarser 

 or finer areolar tissue, and presents a number of cellular portions 

 which can be all inflated from any one point. The middle areolar 

 tissue is usually absent in the upper and lower (or only in the lat- 

 ter) parts of the lung, and the cells are then merely parietal, and 

 leave cavities of considerable size in the interior of the organ. The 

 lungs of the Crocodile and Monitor are the most completely made 

 up of cells. In the Serpents it is commonly only the commencement 

 of the one developed lung that is replete with cells and areolar tissue, 

 its posterior extremity being in the condition of a thin walled and very 

 extensible bladder. The size of the cells varies, but they are always 

 larger than in Birds. 



In the Amphibia, which present the lowest forms of air-breathing 

 animals in the class Vertebrata, the study of the structure of the 

 Larynx as an instrument of voice is one indeed of particular interest. 



Its simplest structure is exhibited by some Ichthyodea, e. g., Pro- 



