71 



marg-in of the biceps will be found the sciatic nerve accom- 

 panied by a blood vessel. Carefully follow the nerve toward 

 the body noting its passage between the pyriformis and the 

 head of the biceps. Follow the nerve up to its connection with 

 the lumbar region of the spinal cord. 



Return to tbe middle of the thigh and note that the nerve 

 sends off a branch which passes along the entensor side of the 

 tibia along the peroneus and beyond. Follow the sciatic and 

 note that at the knee joint it again divides, one branch going . 

 to the. gastrocnemius and the other to the tibialis posticus muscle. 

 The sciatic perve, gastrocnemius muscle and a portion of the 

 femur comprise a nerve-muscle preparation. 



XVIII 



269. Place a frog on its belly and note the movements of 

 the caudal lymph-hearts. They are situated between the 

 hip-joint and the median line in a slight depression. The 

 contractions of these hearts are usually visible through the 

 skin, but are seen more distinctly if the skin is removed with- 

 out injury to the heart. 



Later, note that the lymph-hearts cease to beat after the 

 destruction of the caudal portion of the myel (spinal cord). 



270. Pith the frog. This is accomplished by severing 

 the brain from the myel with a thin bladed knife at the point 

 where the cranium articulates with the atlas. A slight 

 depression will be felt at this point, which will serve .as a 

 guide for the operation. The frog may be firmly held if 

 wrapped in one corner of a towel. 



271. After pithing, lay the frog on its back and cut 

 through the skin on the mid-line, and from the middle of this 

 cut make lateral incisions through the skin. Raise up the 

 end of the sternum and cut, a little to one side of the mid-line, 

 through such parts as may be necessary to expose the heart. 

 Pin the parts out on the side and note the heart beating with 

 some force and regularity. Count the number of heart beats 

 per minute. Pinch up the pericardium with a pair of fine 

 forceps and remove it from the heart. Tilt up the apex of 



