FEOG 245 



At what points do the carotid, aortic, and pul- 

 monary arches unite with the truncus ? 

 Make a drawing illustrating the structure of the 

 heart and the connecting blood-vessels. 



Y. The lymph hearts. 



The study of the lymphatic system is too diffi- 

 cult for the beginner. The posterior lymph 

 hearts, however, are easily found by dissecting 

 away the skin on each side at the posterior end 

 of the urostyle. The pulsations of these organs 

 are sometimes visible through the skin in the 

 living frog. It is best to look for them imme- 

 diately after the frog's death, before they cease 

 moving and partly collapse. 



G. — The Nervous System. 



Select a large specimen which has lain for two 

 or three days in seventy-five per cent, alcohol, 

 portions of the skull and vertebral column hav- 

 ing been removed in order to permit the alcohol 

 to penetrate to the enclosed organs. Clean away 

 all of the dorsal muscles on each side of the ver- 

 tebral column, from the sacrum to the base of 

 the skuU. Eemove the roof of the skull by in- 

 serting the points of fine, strong scissors through 

 the membrane covering the space between the 

 base of the skull and the first vertebra, and mak- 

 ing parallel incisions passing forward on each 

 side from the occipital region to the nostrils. Be 

 exceedingly careful not to run the points of the 

 scissors into the brain. As rapidly as the skull 

 is loosened behind, lift it up with forceps and 

 turn it forward in order to see where to cut. Do 



