REPTILIA 231 



out a csecum; it is clearly divided into large and small intestine. The 

 cloaca is proportionately large. 



The respiratory organs (lungs) are large and complicated. In- 

 halation and exhalation are effected partly by drawing in the neck 

 and thrusting it out again, thus decreasing and increasing the volume 

 of the thoracic cavity. The air is also swallowed into the lungs by 

 filling and then emptjang the throat. 



The circulatory system. The heart is very broad laterally, 

 having two entirely separate atria or auricles, and a ventricle par- 

 tially divided into two parts by a perforated partition. The right 

 auricle receives the venous blood from two precaval and one post- 

 caval veins; the blood then goes to the right half of the ventricle, and 

 thence through the pulmonary artery to the lungs. From the lungs 

 it returns through the pulnaonary veins to the left auricle, thence to 

 the left ventricle, which pumps it out through the paired aortic arches 

 to all parts of the body. There is no renal portal system, but the 

 hepatic portal system is better developed than in the Amphibia. 



The urogenital systems. The kidneys are metanephric bodies, 

 which pass their excretion through paired ureters directly to the 

 cloaca, thence into a urinary bladder, which in turn empties into the 

 cloaca. The male reproductive organs consist of a pair of testes, a 

 pair of much coiled vasa deferentia, through which the sperm passes 

 to the grooved penis, which is attached to the front of the cloaca. 

 The female organs consist of paired ovaries and large oviducts pro- 

 vided with albuminous and shell glands. The eggs when laid are 

 covered with a tough shell and are usually buried in the ground. 



The nervous system shows a considerable advance over that of 

 the Amphibia. The cerebral hemispheres are larger and the cerebel- 

 lum more complete. Many other changes in details will be noted on 

 comparative study. The eyes are small, but the vision is keen; the 

 pupil is round and the iris unusually dark in color. The sense of hear- 

 ing is not very acute; the tympanic membrane is thin and exposed, 

 and is connected with the auditory organ by a slender columellar bone. 

 The sense of smell is the keenest of the senses in most turtles, both 

 in the water and in the air. In correlation with the keen olfactory 

 sense the olfactory lobes of the brain are highly developed. 



