PINE-LIZARD AND ITS ALLIES: REPTILIA 349 



so quick that it is difficult for the eye to follow them. When 

 alarmed the scales can be raised, the throat patches swollen, 

 and the head elevated. The harmless little creature then 

 looks quite formidable. In order to provide for growth the 

 scaly skin is cast periodically. 



Internal Structure. The internal structure is, in general, 

 similar to that of the amphibians, but in several respects it 



FIG. 175. Pine-Lizard. Reduced 



indicates a higher type of animal. Thus, the lizard 

 breathes by lungs at all periods of its life. The 

 heart has a longitudinal partition extending par- 

 tially through the posterior chamber (Fig. 176, 19), 

 so that there is an incomplete separation into right 

 and left ventricles. As in the frog, the left auricle (Fig. 176, 18) 

 receives aerated blood returned from the lungs (Fig. 176, 30) 

 by the pulmonary veins (Fig. 176, 24) and the right auricle 

 receives the blood from the rest of the body (Fig. 176, 25). 

 From the right side of the ventricle arises the pulmonary 

 artery (Fig. 176, 23) ; from the left side are given off the 

 branches of the artery supplying the head and body generally 

 (Fig. 176, 20, 21, 22). When both auricles contract, the venous 

 blood in the right auricle tends to keep to that side of the 

 heart, and, by the aid of the incomplete partition, is forced 

 into the pulmonary artery; the arterial blood from the left 



