THE RABBIT. 247 



auricle. The principal branches of each prgecava are 

 three : (1) a jugular vein coming from the head ; (2) 

 a subclavian vein coming from the shoulder and fore 

 limb ; and (3) a mammary vein coming from the ventral 

 wall of the thorax. The principal branches of the 

 postcava are the short, wide hepatic veins entering it in 

 the liver, the renal veins coming from the kidneys, the 

 spermatic (or ovarian) veins (according to sex) coming 

 from the reproductive organs, and the large external iliac 

 veins coming from the hind limbs. The last-named are 

 called femoral veins posterior to the abdominal cavity. 



Another set of veins, constituting the portal system, col- 

 lects the blood from the digestive organs of the abdominal 

 cavity, and carries it through the portal vein to the liver. 

 This blood percolates through the substance of the liver 

 before being collected again into the hepatic veins. 



II. The Pulmonary System. The blood collected into 

 the right auricle descends, through an opening guarded 

 by a valve, into the right ventricle, whence it is expelled 

 to the lungs through the pulmonary arteries. These arise 

 together from the anterior border of the ventral surface 

 of the auricle, and, arching about the left auricle, separate, 

 and go direct to the lungs. After distribution through 

 the capillaries in the walls of the air cells of the lungs, 

 the blood is collected into the pulmonary veins, and 

 returned directly to the left auricle. The pulmonary 

 artery and vein and connecting capillaries constitute the 

 pulmonary system. The obvious purpose of this part of 

 the circulatory system is the aeration of the blood. 



III. The Arterial System. From the left auricle the 

 blood descends, through an orifice guarded by a valve, 

 into the left ventricle, whence it is expelled through the 

 aorta. The aorta curves dorsally and toward the left side 

 of the body, and then extends posteriorly beneath the 

 dorsal wall and above the viscera. It gives off ante- 



