THE FROG 115 



seen to be one of the two branches into which the prominent fem- 

 oral vein divides. Trace the other branch, the external iliac, for- 

 ward to its point of union with the sciatic vein ; trace the renal 

 portal vein to the kidney. Study the distribution of the femoral 

 and sciatic veins in the leg. Observe the dorsolumbar vein entering 

 the kidney in the middle of its lateral margin, and study its dis- 

 tribution. Observe the oviducal veins, if the animal is a female. 



Exercise 20. Draw a semidiagrammatic sketch showing the renal 

 portal system, together with an outline of the organs with which 

 the veins enter into relations. 



The Pulmonary Veins. The common pulmonary enters the left 

 auricle. It is a very short vein and is formed by the union of the 

 right and left pulmonaries, which come from the right and left 

 lungs respectively. Each pulmonary vein lies along the medial 

 side of the lung, the right pulmonary being somewhat longer than 

 the left. Turn the apex of the heart forward and find these veins. 



Exercise 21. Draw a diagram of the entire venous system. 



The Arteries. 1 All the blood in the heart leaves it through the 

 truncus arteriosus, the structure of which has already been ob- 

 served. At its anterior end the truncus divides into a right and a 

 left branch, each of which, in turn, after passing through the peri- 

 cardium divides into three branches,— the carotid, systemic, and 

 pulmocutaneous aortic arches. The last-named of these arches, 

 which is the hindermost in position, branches off from the others 

 a short distance in front of the pericardium ; the other two usually 

 remain together a short distance before separating. 



The anterior aortic arch, the carotid, passes forward and dorsally 

 a short distance and then divides into two vessels, the internal and 

 external carotid arteries. At this point the walls of the arteries 

 are thickened and spongy, and the ovoid structure thus formed is 

 called the carotid gland ; it is not a gland, however, but probably 

 acts as an accessory heart in that it serves to check and thus to 

 equalize the flow of blood in the carotid arteries. The internal 



ir rhe arterial system can be best studied after it has been injected; this should 

 be done through the ventricle and the truncus arteriosus. 



