388 METAZOAN PHYLA 



4. Testudinata (tes tu di na' ta; L., testudinatus, like a tortoise). — 

 Turtles and tortoises. 



414. Internal Structure. — The heart of a reptile consists of two 

 auricles and a double ventricle (Fig. 272 A), the latter being divided by a 

 septum which, however, is perforated, except in Crocodilia. The blood 

 from the veins enters the right auricle, passes into the right ventricle 

 and thence to the lungs. From the lungs it is returned to the left 

 auricle, goes to the left ventricle, and out through the two aortic arches 

 to the arteries. The blood in the two ventricles mingles to a certain 

 extent, and so mixed blood is sent out over the body. In the Crocodilia 

 (Fig. 272 B), w^here the ventricles are quite separate and the left aortic 

 arch as well as the pulmonary artery arises from the right ventricle, a 

 communication between the two aortic arches permits mixing of the 



Fig. 274. — Six-lined race runner, Cnemidophorus sexlineatus (Linnaeus). A common 

 member of the group of sand lizards which has an extensive distribution occurring in the 

 United States, Mexico, Central and South America. They are fast runners and can dart 

 away from their pursuers very swiftly; this is responsible for the name race runners com- 

 monly applied to them. When seized by the tail by an enemy, they can detach their tail 

 and escape. Detachment of an organ when stimulated is known as autotomy. {Photo- 

 graphed and contributed by George E. Hudson.) 



arterial and venous blood. Renal-portal and hepatic-portal systems are 

 both present, the latter being better developed than in the amphibians. 



The lungs of reptiles are rendered more complex than those of the 

 amphibians by repeated divisions of the bronchi and an increase in the 

 number of the alveoli. This increases considerably the surface through 

 which respiration is carried on. 



The brains of reptiles (Fig. 273) show an advance over those of the 

 amphibians in the better development of the cerebral hemispheres and 

 of the cerebellum. The greatest advance, however, is in the appearance 

 of a cerebral cortex. Here, as a result of the multiplication of the nerve 

 cells and their regular arrangement, the roof of the cerebrum is divided 

 into an outer gray layer and an inner white one. The cells in the gray 

 matter are arranged in distinct groups or areas corresponding to the par- 

 ticular activities which they control. Such a brain roof is called a cortex. 



