The Blood and Lymph. 91 



coats of veins differ somewhat from those of arteries in 

 the tissues present, and thus is accounted for the col- 

 lapsed state of the end of a vein when seen in meat, the 

 end of an artery remaining open. Many veins have 

 valves, especially those of the limbs. When traced to 

 their small branches, arteries and veins are seen to be 

 continued into a network of small blood vessels or capil- 

 laries, therefore for all practical purposes arteries may 

 be said to end and veins to start in these capillaries. 



The pulmonary artery springs from the right ventricle 

 and terminates in the lung by means of small capillaries 

 which are spread over the air cells. 



The main trunk of the arterial system (aorta) starts 

 from the left side of the heart and then divides into an 

 anterior, supplying the front of the body, and posterior, 

 supplying the remainder of the body. The front (ante- 

 rior) aorta divides into branches one to each fore limb, 

 and is continued up the neck, where it again divides 

 into the carotids, and by subdivisions supplies all parts 

 of the head and neck. The arteries given off to the fore 

 limbs (brachials), again divide and are continued as the 

 humerals and later as the radials, it will be noticed that 

 the arteries of the limbs take their names from the bone 

 they are close to, the radials give off the metacarpals at 

 the fetlock, which divide into branches and thus supply 

 the fore feet with blood. 



The posterior aorta is directed backwards and upwards 

 and runs along underneath theback bone until it reaches 

 the loins, where it divides into two trunks, one to each 

 hind limb. Before reaching the loins it has given off a 

 number of branches to supply the stomach, intestines, 



