380 



CROCODILIA. 



arch arises in the right ventricle and after giving off a large 

 visceral artery is connected by a narrow vessel with the right 

 arch (Fig. 209). The pulmonary artery also arises from the right 

 ventricle. Each of these three great arteries is guarded at its 

 ventricular end by two' semi-lunar valves. At the point 

 where the two systemic arches cross one another there is an 



aperture {foramen Panizzae) 

 putting them in communica- 

 tion, so that the arteritil and 

 venous blood are not com- 

 pletely separated. Tlie Croco- 

 dilia are the only Vertebrata 

 with two separate ventricles, 

 and both right and left aortic 

 arches. 

 Crocodiles are fierce rapa- 

 cious animals and live for the 

 most part in fresh water ; the 

 ga\dals being more exclusively 

 aquatic than the crocodiles and 

 caimans. They inhabit the 

 mouths and lagoons of great 

 rivers in the warmer parts of 

 the Old and New Worlds, and 

 seek their prey by night. Some 

 are dangerous to man. They 

 all have a voice which is des- 

 cribed as a " short bark." 

 They appear to grow through- 

 out Hfe which is a long one. 

 The eggs are hard-shelled and 

 are laid in the sand or in holes 

 on the banks. 

 The oldest Crocodilia which appear in the Upper Trias, belong 

 to the Parasuckia and Pseuchsuchia. Though undoubtedly/ 

 Crocodilia, they present some features which are characteristic 

 of the Dinosauria and Rkynchocephalia. The Eusuchia do not 

 appear till the Upper Lias, and the earliest of these possess 

 biconcave vertebrae, and choanae in front of the pterygoids. 

 The earliest crocodiles appear to have been marine, and it is not 



Fig, 209. — Heart and arterial arches of 

 Alligator liiciiis (irom Claus). The right 

 auricle and right ventricle are opened and 

 the arteries springing from the right ven- 

 tricle. Ad right, As left aorta ; Ba dilata- 

 tion on right aorta ; C carotis primaria ; 

 D right auricle ; FP position of foramen 

 Panizzae ; iVf visceral arteries ; opening 

 of sinus venosus into right auricle ; Ov 

 opening of right auricle into right ven- 

 tricle ; P pulmonary artery ; Pc band con- 

 necting to pericardial wall ; S left auricle ; 

 S(l right, Ss left subclavian ; V narrow 

 continuation of left aortic arch after giving 

 off the coeliac artery. 



