46 VETERINARY STUDIES 



The pulmonary circulation is the flow of blood which occurs 

 betw-een the heart and the lungs. 



The systemic circulation is that which occurs between the 

 heart and all the rest of the body, except the lungs. 



Arteries, veins and capillaries. — These are elastic tubes which 

 distribute blood to the tissues and then collect and convey it 

 back to the heart. Arteries have thicker and more elastic walls 

 than veins ; they remain open after death although empty ; the 

 stream flows in jets; the l)lood is lighter in color than that in 

 the veins and flows from the heart and they have no valves. In 

 all these points, the arterial system differs from the venous. 

 Both arteries and veins consist of three coats: outer, fibrous; 

 middle, muscular ; inner, serous. 



Capillaries are the small vessels which connect minute arteries 

 with minute veins. They are generally about one twenty-fifth 

 of an inch in length, and one twenty-five-hundredth of an inch 

 in diameter. 



Blood Supply op the Body 



Arteries. — The aorta is the trunk artery which receives blood 

 from the left ventricle for distribution through the systemic cir- 

 cuit to practically the entire body except the lungs; i.e. except- 

 ing the pulmonary circuit. It is about two inches long and 

 branches into two large trunks, the anterior aorta and the pos- 

 terior aorta. The anterior aorta supplies the head, neck, and 

 front limbs ; and the posterior supplies nearly all the rest of the 

 body. 



The anterior aorta is smaller and shorter (one inch long) than 

 the posterior. Its course is upward and forward. It branches 

 into the right and left axillary arteries. These lie near the 

 trachea, one on each side, for a short distance, and then bend 

 around the anterior borders of the first ribs and terminate at the 

 inner part of each shoulder in the humeral arteries (right and 

 left), which are the continuing branches of the axillary. Each 

 humeral furnishes blood for the corresponding front limb. 



The common carotid arteries, right and left, have their origin 

 in a single vessel, the cephalic artery, which branches from the 

 right axillary near the division of the anterior aorta into right 

 and left axillary arteries. They supply structures in the neck 

 and head. 



A corpuscle, on its way from the heart to the brain, would 



