SANGUIFEROUS SYSTEM. 485 



tal organs, before bifurcating to form the great iliac arteries, 

 and these two great trunks supply numerous branches to 

 the pelvic organs, before leaving that cavity to ramify on 

 the posterior extremities. The form and distribution of the 

 posterior aorta, however, in the perennibranchiate species, 

 and the urodelous amphibia, more closely resemble the 

 course of that vessel in the coccygeal region of fishes and 

 of the larvae of anourous species. 



The sanguiferous system of reptiles is advanced to a higher 

 stage of development than that of the inferior classes of 

 cold-blooded vertebrata, and this superiority is observed 

 chiefly in the magnitude of the pulmonic portion, which 

 accords with the earlier development and the increased ex- 

 tent of their pulmonary organs. The whole heart is pro- 

 portionately larger and broader, and is situated farther back 

 from the head. The auricles are more muscular, more dis- 

 tinctly separated from each other externally, and are more 

 advanced to the anterior part or base of the ventricle, and 

 the ventricle is more divided internally by an ascending 

 septum, than in the amphibia. The general form of the 

 heart, like that of most other viscera, is modified by the 

 form of the trunk, being more elongated in ophidia, broader 

 in chelonia, and intermediate in the saurian reptiles. The 

 right auricle receives the entire venous blood of the system, 

 and the left auricle, the arterialized blood from the capacious 

 pulmonary sacs; the two divisions of the ventricle give 

 origin to the pulmonary and the systemic arteries, which 

 early communicate with each other by means of two deci- 

 duous ductus arteriosi ; and the two principal systemic ar- 

 teries anastamose at a greater or less distance from the 

 heart, to form the common trunk of the descending or 

 abdominal aorta, as in amphibia and fishes. 



The two auricles of ophidian reptiles are generally much 

 extended in a longitudinal direction, and the ventricle also 

 has an elongated conical form; the auricles are provided 

 with distinct muscular bands, and prominent internal fleshy 

 columns ; and the right, which receives the venous blood of 

 the system, is more capacious than the left which receives 

 the arterialized blood from the lungs. The cavity of the 

 ventricle is partially divided by a thick cribriform pervious 

 septum, into a right inferior or pulmonic portion, and a 



