304 CLASS REPTILIA. 



largest. The parietes of these two cavities are slender, and 

 appear transparent in the intervals of the fleshy bundles 

 which consolidate them, and the inter-crossing of which is 

 irregular. A membranous partition separates one from the 

 other. They open, each at the side of the other, by a mouth 

 covered with a semicircular membranous valve, into the ven- 

 tricle, which has the figure of an elongated and not very 

 regular cone, surmounted by an appendage on the left side 

 of its base, and divided internally into two lodges, one upper 

 and one lower, which are separated but in part by an incom- 

 plete horizontal partition, composed of fleshy bundles between 

 which the blood can pass. The interior of these lodges is 

 traversed in all directions by a multitude of muscular 

 columns, which strengthen its parietes, and concur to pro- 

 duce a more intimate mixture of the blood which comes 

 from the lung, with that which arrives from the rest of the 

 body. 



The orifice of the pulmonary artery corresponds to the 

 lower lodge. The left aorta springs from the same lodge 

 immediately below the right, which commences in the upper 

 lodge, and which thus receives a portion of the blood of 

 the lungs and body before its passage into the lower lodge, 

 from which it is expelled into the left aorta and the pul- 

 monary artery. 



In consequence of the absence of sternum and diaphragm, 

 the mechanism of respiration is altogether different in the 

 ophidians from what it is in mammalia and birds. They have, 

 moreover, but one lung, which is prolonged above the oeso- 

 phagus, the stomach and the liver, and considerably beyond 

 the two last. The trachea consequently is not divided into 

 branchiae, and when arrived at the single lung, it terminates 

 abruptly in the cavity of the viscus. Its parietes are very 

 membranous, for there are no fibro-cartilaginous portions 

 found in it, except in the lower third of its circumference. 



