CIECULATORy SYSTEM 415 



a. The gastro-duodenal vein returns the blood from 



the right side of the gizzard, from the duodenum 

 and from the last loop of the small intestine. 



b. The anterior mesenteric vein returns blood from 



the greater part of the length of the small in- 

 testine. 



c. The posterior mesenteric vein returns blood from the 



hinder part of the small intestine, and from the 

 rectum. The blood in the anterior part of this 

 vein flows forwards to the portal vein, that in the 

 hinder part backwards to the hypogastric veins. 



4. Veins opening into the left auricle. 



The pulmonary veins, which are extremely short, 

 open into the posterior surface of the left auricle. 



Twm the heart forwards : open the left auricle : wash out 

 the contents ; and pass a seeher along the pulmonary veins 

 into the lungs. 



C. The Arteries. 



1. The pulmonary artery is a single trunk, which arises 



from the anterior end of the right ventricle, close 

 to the ventral surface and a little to the left of the 

 median plane. It divides soon after its origin into 

 right and left arteries. 



a. The left pulmonary artery is short, and passes 



direct to the left lung, which it enters in front 

 of the pulmonary vein, and ventral to the left 

 bronchus. 



b. The right pulmonary artery passes dorsal to the 



other arterial trunks, to enter the right lung in 

 front of the bronchus. 



2. The aorta arises from the base of the left ventricle, 



lying between the two auricles, and to the right 

 of, and slightly dorsal to, the pulmonary artery. It 

 gives off almost immediately the very large right 

 and left innominate arteries, and then continues its 

 course as the dorsal aorta. 



