408 



COLLEGE ZOOLOGY 



OJI 



Edge of dorsal 

 carapace 



Opening for 

 foreleg r- 



Opening for \ 

 hindleg '■ 



>'••'■* 



Horny scutes 



Bony plates 

 (scutes removed) 



Horny scutes 



Bony plates 

 (scutes removed) 



Plastron (ventral viev/) 



Corapace (dorsal view) 



Figure 275. Turtle shell showing the external horny scutes and the bony plates beneath. The 

 living epidermis, which covers the bony plates, produces the horny scutes. 



two posterior nares are situated in the an- 

 terior part of the roof of the mouth. At the 

 base of the tongue is a longitudinal slit, the 

 glottis, and a short distance back of the an- 

 gle of the jaw are the openings of the 

 Eustachian tubes. The pharynx is thin- 

 walled and very distensible; it leads into the 

 more slender and thick-walled esophagus. 

 The stomach opens by a pyloric valve into 

 the small intestine; this is separated from 

 the large intestine bv the ileocecal valve. 

 The terminal portion of the digestive canal 

 is the rectum; it opens into the cloaca. 

 There is no intestinal cecum. 



The liver discharges bile into the intes- 

 tine through the bile duct. Several pancre- 

 atic ducts lead from the pancreas to the 

 intestine. 



Circulatory system 



The reptilian heart (Fig. 222), except in 

 the case of the Crocodilia, consists of two 



atria and a single ventricle which is divided 

 into two by an incomplete septum. In the 

 crocodilians the longitudinal septum in the 

 ventricle is complete, forming a 4-cham- 

 bered heart. The venous blood from the 

 body (Fig. 276) is carried by the posterior 

 vena cava and the two anterior venae cavae 

 into the sinus venosus and thence into the 

 right atrium. From here it passes into the 

 right side of the ventricle, and when the lat- 

 ter contracts, it is forced out through the 

 pulmonary artery which sends a branch to 

 each lung and through the left aorta which 

 conveys blood to the viscera, and into the 

 dorsal aorta. 



The blood which is oxygenated in the 

 lungs is returned by the pulmonary veins to 

 the left atrium and thence into the left side 

 of the ventricle. This blood is pumped out 

 through the right aortic arch, which merges 

 into the dorsal aorta. Because the septum 

 dividing the ventricle into two is incomplete, 

 the blood that enters the right aortic arch is 



