492 ZOOLOGY. 



True lips now, as in birds, border the jaw-bones, while 

 salivary glands for the first time in the Vertebrates appear 

 in the Chelonians and lizards ; besides these there are smaller 

 glands in the lips of lizards and snakes, the poison-glands 

 of the rattlesnake, viper, etc., being modifications of these 

 labial glands. 



While the oesophagus is wide and the stomach usually 

 quite simple, in the crocodiles there is a muscular gizzard 

 approaching that of birds, and there is a special pyloric por- 

 tion in the crocodiles like that of grallatorial and swimming 

 birds. The liver and pancreas have, as in birds, two or more- 

 excretory ducts, and a gall-bladder is always present. A 

 large fat-body (Fig. 440, /) is present on each side of the 

 body. 



The lungs, trachea, and larynx of reptiles are much 

 simpler than in birds ; in the long slender-ringed trachea 

 there is an approach to that of birds, but the lungs are 

 modelled on the Amphibian type ; the larynx, especially la- 

 the Chelonians and crocodiles, is much more perfect than in 

 the Amphibians. 



The organs of circulation show a decided advance in situ- 

 ation over the Batrachians. The heart (Fig. 440) recedes 

 farther back into the thorax. Of the two auricles the right 

 and larger one receives the systemic and the left the pul- 

 monary veins. In all but the crocodile the ventricle has 

 a partition, the right half containing venous and the left 

 arterial blood, while in the crocodiles there are two ven- 

 tricles, so that the heart is four-chambered. In the lizards 

 two aortic branches (a right and a left) survive. In the 

 crocodiles a vessel which gives off the right aortic arch and 

 the carotids arises from the left ventricle, while a left aortic 

 arch and the pulmonary arteries arise from the right ven- 

 tricle. In the reptiles as in birds there are two superior as 

 well as one inferior vena cava. In reptiles as in lower Ver- 

 tebrates there are no true lymphatic glands ; an organ re- 

 sembling them is present in reptiles (Fig. 440, th), forming a 

 small swelling situated behind the angle of the lower jaw. 



While the brain is still simple, though it fills the cavity of 

 the skull, the different lobes being subequal in size, the cere- 



