Sauropsida: Class Keptilia 



465 



impossible through such a horny layer as that of reptiles. Modern 

 reptiles do not at any time of life breathe by gills. On the walls of the 

 temporary embryonic pharyngeal clefts have been observed minute 

 papillae which can be interpreted as vestiges of gill-filaments, but 

 nothing approaching functional gills appears in any reptilian embryo. 

 In the adult reptile, therefore, respiration must be entirely pulmonary, 

 unless in some cases (probably so in sea turtles) the buccopharyngeal 

 surfaces are auxiliary to the lungs. Consistent with their prime im- 

 portance, the lungs are much more highly developed than in amphib- 

 ians. They have greater capacity, relative to the size of the animal, and 

 their respiratory surface is greatly increased by development of parti- 

 tions which divide the internal space into numerous communicating 

 chambers (Fig. 358). 



With concentration of the respiratory function in the lungs, it 

 becomes increasingly important that the heart should be so arranged 

 that the oxygenated blood received from the lungs will be distributed 

 into the general circulation, while the venous ("impure") blood re- 



A BCD 



Fig. 358. (A) Lungs of Sphenodon (after Gegenbaur); the left lung opened to 

 show the alveoli. (B) Left lung of Iguana. (6) Bronchus; (c) internal opening of 

 bronchus; (d, v) dorsal and ventral chambers; (s) septum. (C) Diagram of longi- 

 tudinal section through lung of lacertilian. (a, p) Anterior and posterior saccular 

 extensions of bronchus; (far) lateral external bronchus; {Ibr) lateral secondary 

 bronchus leading to air-cells; (mbr) main internal bronchus. (D) Lung of Cha- 

 maeleon (Wiedersheim). (b) Bronchus, dividing into three bronchi (c) which 

 open into the three chambers formed by the incomplete septums (s). (A, B, D, 

 courtesy, kingsley: "Comparative Anatomy of Vertebrates," Philadelphia, The 

 Blakiston Company. C, from Goodrich: "Studies on the Structure and Develop- 

 ment of Vertebrates." By permission of The Macmillan Company, publishers.) 



