488 SANGUIFEROUS SYSTEM. 



enveloping pericardium, to a greater extent from their origin, 

 before they separate for their respective destinations. The 

 thick parietes of the ventricle are loose, cribriform and deeply 

 cancellated in their interior, from the free and detached condi- 

 tion of the irregular fleshy columns which compose them ; 

 and the pulmonic and systemic portions of the blood are 

 mingled together in its cavity, to a variable extent in different 

 species, according to the development and the direction of 

 its imperfect septum. The right and left aortse, provided 

 with semilunar valves at their origin, commence by distinct 

 orifices in the common cavity at the base of the ventricle, 

 and unite together under the vertebral column after forming 

 a small arch upwards on each side, the left giving off no 

 branches till near the place of its anastomosis with the right, 

 to form the common descending aorta. The two common 

 carotids arise from the arch of the right aorta, and the sub- 

 clavian arteries come off from the right and left trunks of 

 the aorta at the angle of their reunion. The common trunk 

 of the posterior aorta in passing backwards gives off the in- 

 tercostals on each side, a branch to the cesephagus and 

 another to the liver. The coeliac and anterior mesenteric 

 originate by a common trunk, which is succeeded by the 

 lumbar, the spermatic, and the posterior mesenteric arteries. 

 From the posterior position of the kidneys the renal arteries 

 come off late, and are succeeded by the two common iliacs, 

 the aortal trunk being here prolonged as a large median 

 sacral artery, corresponding with the magnitude of the caudal 

 prolongation of the body in these lacertine reptiles. 



The heart of the crocodilian reptiles is enveloped in a very 

 thick and strong pericardium, which also firmly connects 

 together all the great arterial trunks which originate from its 

 cavity. The parietes of the auricles, especially the right, 

 are furnished with strong muscular internal bands, and there 

 are large semilunar valves at each of the auriculo-ventricular 

 orifices. The ventricle has very thick muscular parietes, and its 

 cavity is^divided by a strong muscular and columnar septum 

 deeply pitted, which extends from the apex to the base of the 

 heart. The right auricle is much larger than the left, which cor- 

 responds with the greater size of the veins and the larger 

 quantity of blood, which enter the former cavity, and the two 

 cavities of the ventricle still communicate with each other 



