574 REPTILES. 



form the dorsal aorta. The carotid arches supply the head 

 region with blood. From the base of the truncus arteriosus, 

 the right and left pulmonary arteries also arise (Fig. 249). 



From the light aortic arch as it curves round, arise the right and left 

 subclavian arteries, which carry blood to the fore-limbs. A coeliaco- 

 mesenteric artery arises from the dorsal aorta and supplies the viscera. 

 Smaller vessels are also given off to the genital organs, etc. , and then at 

 the anterior end of the kidneys the aorta divides into two femoral 

 arteries, which break up into a network of small vessels, supplying hind- 

 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 venae cavse. 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 

 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. 



A lymphatic system, including a pair of lymph hearts, is present. 



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 (Chamaeleon and Geckos) the 

 lungs are prolonged in air-sacs, suggesting those of Birds 

 (Fig. 250). 



Excretory system. — The paired kidneys lie in the 

 extreme posterior region of the abdominal cavity, and 

 extend a little further back than the level of the cloaca. 

 Each is furnished with a very short ureter. In the male the 

 ureters unite with the vasa deferentia ; in the female they 

 open separately into the cloaca. Into the cloaca opens also 

 a large thin-walled "urinary bladder" : this is a remnant of 



