490 SANGUIFEROUS SYSTEM. 



clavial artery, on each side. Sometimes the carotids of both 

 sides, arise by a common trunk as in serpents. The subclavian 

 artery gives off an oesophageal, an internal mammary, an 

 inferior cervical and an anterior common intercostal branch, 

 before arriving at the axilla, where it sends off several thoracic 

 branches, and forms the brachial, which divides as usual into 

 the radial and ulnar arteries. The trunk of the right aorta, 

 near its place of union with the left, gives off a considerable 

 posterior common intercostal artery, which is succeeded by 

 two smaller branches, distributed also on the intercostal 

 spaces. The left aorta gives off no branches before it arrives 

 near the place of its anastomosis with the right, where it 

 gives off the great coeliac, or visceral artery, which supplies 

 most of the abdominal organs, as the stomach, the liver, the 

 spleen and the pancreas, and leaves only a small and short 

 communicating branch to unite with the right trunk of the 

 aorta. The anterior mesenteric arises from the common 

 trunk of the united aortse at some distance below the coeliac 

 artery, and is followed by the supra-renal, the renal, and the 

 lumbar arteries, and the profunda femoris, before the aorta 

 gives off the great crural artery on each side to the legs. 

 The posterior mesenteric and the coccygeal arteries arise 

 from the median sacral, which here forms a large prolonga- 

 tion of the aorta, corresponding with the magnitude of this 

 part of the body in the crocodilian reptiles. 



The short and broad form of the heart in the chelonian 

 reptiles accords with the great transverse development of 

 their body, and with the broad form of the auricle and ven- 

 tricle already seen in the highest plagiostome fishes, the 

 rays and sharks, which prepares for the division of the ven- 

 tricle into two distinct cavities in the hot-blooded classes. 

 The entire venous blood of the tortoise is conveyed by the 

 two large inferior and the two smaller superior vena cavae 

 (FiG. 139././. g. y.} into the common sinus venosus, and 

 thence by a single orifice into the capacious right auricle 

 (139. .) of the heart. The smaller left auricle (139. b.) 

 receives the arterialized blood from the two pulmonary veins 

 (139. d. e.), and both auricles pour their contents simulta- 

 neously into the strong muscular and single ventricle 

 (139. c.), which propels the blood, by three distinct orifices, 

 into the right (139. /*.) and left (139. /.) aortee and the 



