VASCULAR SYSTEM. 



325 



sinus venosus, two auricles and, except in crocodiles, of a single 

 ventricle. It therefore resembles the amphibian heart, but it 

 differs from this in the absence of a conus arteriosus and in the 

 fact that the division of the ventral aorta which has commenced 

 in the Amphibia (particularly in the Anura) is completed and 

 the ventricle gives off three separate arteries, the right and left 

 systemic aortae and the pulmonary. 



Both right and left systemic aortic arches persist, but the right 

 is the most important and alone gives off the carotids and sub- 

 clavians. The left arch either gives 

 off no vessels, or at most only the 

 coeliac artery (Chelonia, Crocodilia, 

 Fig. 179) close to its union with the 

 right arch. In the Crocodilia the 

 ventricular septum is complete and 

 there are two separate ventricles. 

 Of these the right gives off the 

 pulmonary artery and the left sys- 

 temic aorta, while the right aorta 

 arises from the left ventricle. But 

 the separation of the two sides is not 

 complete, for the two sytemic aortae 

 communicate by a small aperture, 

 the foramen Panizzae, where they 

 cross one another, just beyond the 

 semilunar valves The venous sys- 

 tem * is very similar to that of 

 Amphibia. There are two superior 

 venae cavae (ductus Cuvieri), an 

 inferior vena cava which arises in the 



kidney, and a renal-portal system, which however is reduced 

 in Chelonia, the greater part of the blood of the iliac veins 

 passing to the liver. There is a single or double anterior 

 abdominal vein which joins the portal system. All the venous 

 blood of the hind end of the body passes through the kidneys or 

 the liver. 



Fio. 179. Heart and Arteries of a 

 Chelonian (Chelydra). d right, 

 s left auricle ; c carotid ; alright, 

 as left aortic arch ; pd right, 

 ps left pulmonary artery ; c 1 

 coeliac artery ; sd right, s s left 

 subclavian artery (from Cegen- 

 baur). 



In the snake? and lizirJb the anterior abdominal vein is single, and 

 does not anastomose with the cauial and iliac veins, which are distributed 



* Rathke, Bau u. Entwick. des Venensystem der Wirbelthiere. Konisberg, 

 1838. Hochstetter, Morph. Jahrb., 13, 17, and 19. 



