different part-*. Measure its total length, and compare with the 

 length i it the hody. Kxamine the alimentary canal of a tadpole. 

 What is it- length, mea-nred in unit- of length nf the hody (with- 

 out the tail)? How docs it compare in relative length with that 

 of the fr g? \Vhy the difference ? 



l-'.\amine also the lungs of the frog. Inflate them. Note their 

 -ac-like character, and the internal ridge-, which contain hlood 

 \ essels. 



li. CIRCULATORY SYSTEM 



I. PHYSK >L< ><;V ( >F Till-; 1IKART BEAT. 



jo_>. The fi'oi/'s heart. I'ith a frog, heing careful to av< id 

 loss ->f hlood. Plug the hrain with cotton if any occurs. \< >w 

 c\po>e the heart hy cutting through the hody wall to one side of 

 the middle line i to avoid abdominal vein >, turn the pectoral girdle 

 to one side and remove if necessary. Note the pericardium sur- 

 rounding the heart. Carefullv cut through the pericardium expos- 

 ing tlie heart. X< >te a slender hand of connective tissue running 

 het ween the dorsal surface of the heart and the pericardium the 

 fracnum. Tie a thread tightly around this; then divide the fraeiium 

 d"i'sal to the ligature. C-e the thread f r turning the heart over 

 or otherwise handling it. Study carefully the anatomy of the 

 organ; draw fn m dorsal and ventral aspects. Note right and left 

 auricle, junction of three venae cavae to form the -inns venn-u-. 

 -ingle truncu- arterio^us, hifurcation of the latter and suhdivision of 

 each hranch into three arterial trunk- carotid, aortic and pulmo- 

 cutaneous. He sure you understand the anatomy of the organ, 

 nhserve the whitish crescent at the junction of -inn- and right 

 auricle. 



a. Study carefully the -c<|Ucncc of the heats of the different 

 chamhers. Close ohservation is needed here. Xote any change 

 in color, si/.i- and form of the ventricle during sv-tole and diastole 

 respectively. 



h. Count the numher of heats per minute. \<>w excise the heart, 

 cutting wide of the -inu- after lifting hy the ligature. Place the 

 ' rgan in a -mall gla-- ve--cl with Ringer's solution. I la- e\ci-ion 

 altered the rate of heat? Kee|> the heart for use in experiment 

 21 5 h. 



_''>}. '/'//r turtle's heart. l ; .\pose the heart of a turtle without 

 lo-- df hlodd and familari/e your-elf \\ith il- -tructure and sei|iience 

 of heat as in the frog. That niav he done as follows: Pith, hv 



go 



