xiv. 7 CIRCULATION 379 



into a larynx with supporting cricoid and arytenoid cartilages. Many 

 reptiles are able to produce small sounds, but the voice-box is less 

 developed than in either amphibia or birds. 



The lungs are sacs whose walls are folded into ridges, separating 

 a number of chambers or bronchioles. The hinder part of the lung is 



car. int. 



car. ex t. 



Fig. 215. Diagram of heart and arteries of Lacerta. 



car.ext. external carotid; car. int. internal carotid; c.car. common carotid; coel. coeliac artery; 



d.a. dorsal aorta; d.B. ductus Botalli (arteriosus); d.car. ductus caroticus; l.aur. left auricle; 



p.a. pulmonary artery; p.v. pulmonary vein; r.aur. right auricle; scl. subclavian artery; 



sept, interventricular septum; v.c. eaval veins. (From Ihle, after Goodrich.} 



nearly smooth and in some lizards, as in birds, it becomes developed 

 into characteristic air sacs. The tendency is for the more anterior por- 

 tion of the lung to become the effective vascular and respiratory region, 

 allowing the air-stream to be drawn across it at both inspiration and 

 expiration. 



The circulation (Fig. 215) of lizards shows a partial separation of 

 venous and arterial blood; there are two auricles, but only one ven- 

 tricle, this being partly divided by a septum into right and left sides. 

 Three arterial trunks arise directly from the ventricle, these being the 



