SANGUIFEROUS SYSTEM. 495 



each side, it is continued along the sacrum and coccyx as a 

 small median caudal artery, as in other reptiles. The in- 

 ternal iliac ramifies mostly on the urinary bladder and other 

 pelvic viscera, and the external iliac, after giving off the 

 epigastric and circumflex arteries, and continuing to afford 

 numerous branches to the thigh and leg as crurial and an- 

 terior tibial artery, terminates in a dorsal arch, extending 

 outwards over the tarsus, from which the digital arteries of 

 the foot are derived. 



The venous blood returned from the head and neck by 

 the jugular veins (B. t. u.) in the chelonia, as in other rep- 

 tiles, and that brought from the arms by the subclavian veins 

 (B. v. w.) 9 is conveyed by the right and left anterior or superior 

 venee cavee (139. g. g.}, formed by the union of these two 

 veins on each side, into the common sinus venosus (141. 

 B. z.) } which receives the blood from the abdominal veins. 

 The abdominal veins receive the blood from the posterior 

 parts of the body, and from the renal and hepatic portal 

 systems, and, after communicating on each side with the 

 jugular veins by an anastomosing branch, they enter the sinus 

 venosus, which pours its contents by a single broad valved ori- 

 fice into the right auricle of the heart (A. a.) The two pulmo- 

 nary arteries (B. p. q.} arise by a lengthened single bulbous 

 sinus from the left inferior part of the right ventricle, and, 

 after communicating by the ductus arteriosi (B. r. s.) with 

 the two aortse (B./. #.), they follow the ramifications of the 

 bronchi through the extensive cavities of the lungs. The 

 two small returning pulmonary veins (B. 1. 2.) unite to form 

 a small sinus before entering by a single opening into the 

 left auricle. The veins of reptiles, like their chyliferous and 

 lymphatic vessels, are provided with scanty and ineffective 

 valves, which allow injections to pass readily against their 

 course, from trunks to branches. 



In the class of birds, the septum of the ventricles is at 

 length completed, and the pulmonic circulation is entirely 

 distinct from the systemic, as in all the hot-blooded verte- 

 brata. The air admitted into contact with the systemic capil- 

 laries in the interior of the bones and in the large air-cells 

 extending through most parts of the body, oxygenates and 

 decarbonizes a larger portion of their blood, and is the source 

 of their high temperature, their great muscular force, and 

 the encreased energy of all their functions. By their 



