RESPIRATORY SYSTEM 627 
limbs and kidneys, and finally, at the posterior end of the kidneys, 
reunite to form the caudal artery, which runs down the tail. 
The blood from the anterior region of the body is returned to the 
heart by the right and left precaval veins or superior venze cavee. The 
right precaval is formed by the junction of external and internal 
jugulars with the subclavian vein ; on the left side the jugular is absent. 
From the posterior region of the body, blood is brought back by the 
postcaval vein or inferior vena cava. The three great veins open into a 
thin-walled sinus venosus, which opens into the right auricle. 
The postcaval is formed by the union of two veins which run along 
the genital organs, and receive renal veins from the kidneys. In pass- 
ing through’the liver the postcaval receives important hepatic veins. 
From the tail region the blood is brought back by a caudal, which 
bifurcates in the region of the kidneys into two pelvics. The pelvic 
veins give off renal-portals to the kidneys, and receive the femoral and 
sciatic veins from the hind-limbs. They then unite to form the 
Fic. 343.—Lung of Chamaleo vulgaris, showing air-sacs. 
—After Wiedersheim. 
epigastric or anterior abdominal, which carries blood to the liver. 
Except through the medium of the renal-portal system, there is no 
connection between the anterior abdominal and the postcaval. To the 
liver, blood is carried as usual from the stomach, etc., by the portal 
vein. ; . 
From the lungs blood is brought to the left auricle by the pulmonary 
veins. 
There is, as usual, a lymphatic system, including a pair of lymph hearts. 
Respiratory system. — The lungs are elongated oval 
structures which taper away posteriorly. The mouth does 
not, as in the frog, play an important part in the respiratory 
movements. In some lizards (Chameleon and Geckos) the 
lungs are prolonged in air-sacs, suggesting those of Birds 
(Fig. 343). . ioe 
Excretory system. — The paired kidneys lie in the 
extreme posterior region of the abdominal cavity, and 
