THE FROG 19 



internal carotid arteries. Follow the external carotid into the 

 lower jaw, the external dorsally to the posterior end of the head. 

 In the same way follow out the pulmo-cutaneous arch to its 

 division into the pulmonary artery going to the lungs and the 

 great cutaneous artery which ascends alongside the cucularis 

 muscle. How many branches to the pulmonary artery before 

 it enters the lungs? After these vessels have been dissected 

 out the ramifications of the internal carotid may be followed. 

 Then follow the radix aortae, note and follow the subclavian 

 artery into the fore limb and the main trunk of the radix to the 

 union with its fellow to form the dorsal aorta. 



Sketch these vessels in the arterial drawing. Your two 

 sketches should now present the main arterial and venous trunks 

 of the body. 



The heart should now be studied in the uninjected specimen. 

 Cut the connecting vessels (cavae, pulmonary veins, and the 

 great arterial trunks beyond their division into carotid, radix, 

 etc.) and remove heart from body. 



Note the position of the entrance of the cavffi and the 

 pulmonary veins and of the giving off of the truncus arteri- 

 osus impar. Cut across the two paired arterial trunks close to 

 their origin from the unpaired trunk and note the cut ends. 

 Are they simple tubes? What relations do you recognize to vessels 

 already seen? 



Pin the heart out under water, the ventral side uppermost, 

 and carefully dissect away the ventral side of the auricles, ventricle, 

 and the bulbus. Wash out the coagulated blood. 



Are the two auricles completely separated by a partition 

 (interauricular septum)? Which one connects with the sinus 

 venosus? What relative difference is there in the positions of 

 the sinu-auricular opening and that of the pulmonary veins? 



Is there a separate opening (auriculo-ventricular canal) from 

 each auricle into the ventricle? To settle this examine first the 

 auricles and then the ventricle. How are the differences to be 

 explained? Which has relatively the thicker wall, the right or 

 left auricle or the ventricle? 



In the bulbus cordis notice a longitudinal, somewhat twisted 

 fold, the spiral valve or septum bulbi, practically dividing the 

 bulbus into right and left halves. Probe through the cut ends of 

 the arterial trunk with three bristles and note where each appears. 



