THE ANATOMY OF THE LIZARDS 19 



consisting of two lobes. The ducts from these urino- 

 genital organs open into the cloaca. 



The three-chambered heart consists of a single 

 ventricle and two auricles, right and left. Three 

 main arteries come from the base of the ventricle, 

 namely, the pulmonary artery carrying blood to the 

 lungs, and the right and left aortse. These two vessels 

 after arching to either side, bend round the gullet, 

 and unite to form one vessel, the dorsal aorta, which 

 distributes the blood, by means of its branches, to the 

 posterior part of the body. The great veins which 

 bring the blood to the heart, empty into a venous 

 sinus, or directly into the right auricle. 



The respiratory system consists of a windpipe or 

 trachea, which divides into two bronchi, and each of 

 these communicates with the corresponding lung. Each 

 lung is a very thin sac, the posterior part being the 

 thinner, the walls of which are made up of a network 

 of ridges, which support the vessels through which the 

 exchange of oxygen and impure products takes place. 



If the brain be exposed by removing the roof of the 

 skull, we note from before backwards the olfactory 

 lobes, cerebral hemispheres, the pineal body, optic 

 lobes, small cerebellum, and the medulla oblongata, 

 this last being continuous with the spinal cord. 

 Various cranial nerves will be seen emerging. 



The foregoing are the principal points which the 

 field naturalist will be concerned with. Those who 

 wish to examine in greater detail the anatomy of a 



