566 TEXTBOOK OF ZOOLOGY 



vided into an anterior and posterior chamber. The anus is the pos- 

 terior end of the alimentary canal. 



The pancreas is an elongated branched body of glandular material 

 located within the first loop of the intestine between the stomach 

 and the duodenum. It secretes an alkaline digestive fluid which is 

 emptied into the duodenum. 



The liver is a larg'e, bilobed organ divided imperfectly into right 

 and left lobes. It secretes bile, an alkaline digestive fluid. This fluid 

 is stored in the gall Madder until food enters the duodenum. It then 

 passes into the intestine through the common bile duct. 



Respiratory System 



A basic feature that distinguishes reptiles and other higher ver- 

 tebrates from amphibians and fish is that they do not breathe by 

 gills during development. The respiratory system of all lizards is 

 typical of air-breathing vertebrates. A tubular trachea conducts 

 air from the mouth to the highly vascularized lungs. This tube is 

 prevented from collapsing by rings of cartilage. A gaseous ex- 

 change is effected between inhaled air and the blood. The oxygen 

 is absorbed and carbon dioxide exhaled. Breathing is effected by 

 the motion of the ribs. Air passes through the nostrils, or external 

 nares, into the olfactory chaml)er. From there it passes through the 

 internal or posterior nares into the mouth cavity to be forced 

 from there through slitlike glottis into the chamber of the larynx. 

 The larynx continues posteriorly as the trachea, which lies in the 

 midventral line of the throat and extends to the lungs. The posterior 

 end of the trachea bifurcates to form two smaller tubes, the right 

 and left hronchi. Each bronchus connects with a corresponding lung 

 a short distance from the apex of the lung. Within the lung each 

 bronqhus divides into secondary bronchi and these in turn give off 

 tertiary branches. The smallest tubules, bronchioles, carry the air 

 into air spaces or alveoli. It is in the alveoli that an exchange of 

 gases takes place. 



The Circulatory System 



The circulatory system of reptiles shows distinct advances over 

 the circulatory system of amphibians. Since respiration is carried 

 on exclusively by the lungs, changes which are in keeping with this 



