XXX. CIRCULATION 



Cat. A. 



P. A. 



The Organs of Circulation in the Frog. — In a frog that has been recently 

 killed the organs of circulation may be made out in part. It is best, how- 

 ever, to have a specimen in which the blood vessels have been injected with 

 some semifluid mass (made of gelatine or starch colored with carmine 



or other bright coloring material). Two speci- 

 mens should be used to demonstrate the organs 

 of circulation, one for the veins, the other for the 

 arteries. In a specimen killed by chloroform- 

 ing find the nearly triangular-shaped heart. It 

 is seen to be composed of two distinct parts, 

 a light-colored area, the ventricle, and a broader 

 portion, which is darker in color. This latter 

 area is made up of the two auricles. Compare 

 the two areas of the heart in position. The 

 auricles, according to their position, are called 

 respectively the right and left auricles. 



The arterial system of the frog may be said to 

 include all blood vessels which carry blood away 

 from the heart. The heart is only imperfectly 

 divided into a right and a left heart, there being 

 only one ventricle, with an imperfect partition 

 wall extending in an anterior-posterior direc- 

 tion. Blood leaves the heart to pass to the 

 lungs by a vessel (shown in the diagram), known 

 as the pulmo-cutaneous trunk, because it carries 

 blood to the skin and lungs. Over the ventral 

 surface of the heart is found a large common 

 trunk, the conus. This divides into two branches 

 while still over the heart, and then each branch 

 splits into three large arteries, the carotid, sys- 

 temic, and pulmo-cutaneous appearing from the 

 midline as we go outwards. Trace the course 

 of the carotid artery; it supplies the head and 

 neck with arterial blood. The systemic arteries 

 are the most important in the body. Trace one 

 backward to where it unites with its neighbor 

 on the opposite side of the body to form the 

 dorsal aorta, the great main trunk supplying 

 the organs of the body cavity and the muscles 

 of the body and legs. Find the branches passing to the stomach, intestine, 

 liver, and other organs held in the mesentery. Farther back, arteries may 

 be found that pass to the kidneys and genital organs. The aorta divides 

 to form two large trunks, the iliac arteries, that supply the muscles of the 

 hind legs. Make a drawing to show the principal arteries and their con- 

 nection with the heart of the frog. 



The system of blood vessels which return blood from the various organs 

 of the body to the heart is known collectively as the venous system or veins 



350 



Arterial system of the frog; 

 Cat. A., carotid artery; 

 D.A., dorsal aorta; 

 D.T.A., artery to diges- 

 tive tract; IL., iliac artery; 

 L., lungs; K., kidney; 

 P.A., pulmonary artery; 

 R.A., renal artery; V.H., 

 ventricle of heart. (After 

 Parker and Haswell.) 



