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MANUAL OF ZOOLOGY 



which is supported by numerous cartilaginous rings. The 

 anterior part of this is dilated to form the larynx, which 

 is supported by certain special cartilages the cricoid 



and the arytenoids. The 

 trachea bifurcates posterior- 

 ly to form two bronchi, 

 right and left, one passing 

 to each lung. 



The lungs of the Lacer- 

 tilia and Ophidia are sim- 

 ple and sac-like, like those 

 of the Frog. In the Croco- 

 dilia and Chelonia they are 

 of a more complex char- 

 acter, being divided inter- 

 nally by septa into a number 

 of chambers. 



In the heart (Fig. 253) 

 the sinus venosus is always 

 distinct, and is divided into 

 two parts by a septum ; 

 its aperture of communica- 

 tion with the right auricle 

 is guarded by valves. There 

 are always two quite dis- 

 tinct auricles, as in the 

 Amphibia, the right re- 

 ceiving the venous blood 

 from the body, the left the 

 oxygenated blood brought 

 from the lungs by the pulmonary veins. But a vital point of 

 difference between the heart of the Reptile and that of the 

 Amphibian is that in the former the ventricle is always more 



FIG. 253. Heart of Monitor (Varanus) 

 dissected to show the cavity of the 

 ventricle and the vessels leading out 

 from it. A. A', auricles; Ao. dorsal 

 aorta ; Ap. Ap'. pulmonary arteries ; 

 Asc. subclavian artery ; Ca. Ca'. caro- 

 tids; RA. RA. roots of dorsal aorta; 

 Trca. innominate trunk ; V. ventricle ; 

 t, right aortic arch ; *, left aortic arch. 

 (From Wiedersheim's Comparative 

 Anatomy.) 





