RESPIRATION. 



the upper end of the sternum. Pull the sterno-mastoid and other 

 longitudinal neck muscles toward the median line. Pull the skin 

 and other muscles to one side and expose the cervical spinal nerves 

 and -the beginning of the brachial plexus. The carotid artery, 

 vagus nerve, and jugular vein should also be pulled toward the 

 median line. Determine the position of the fourth, fifth, sixth, 

 and seventh cervical nerves. Arising by filaments from the pos- 

 terior divisions of these nerves, a fine nerve fibre will be seen run- 

 ning over the heavy spinous muscles, parallel with the spinal col- 

 umn and disappearing under the clavicle. To make sure that you 

 have found the phrenic nerve, place fine platinum electrodes under 

 this nerve filament and stimulate with medium strong single-in- 

 duction shocks. The diaphragm recorder which records the move- 

 ments of the right side of the diaphragm will move with each 

 stimulus. 



2. Pass a thread around the upper origin of the nerve. Tie the 

 nerve and sever all connection with the cervical nerves. Note the 

 diminution or complete loss of recorded movement of the dia- 

 phragm. The right side of the diaphragm is paralyzed and moves 

 only as it is pulled upon by the side which is still active. Compare 

 the thoracic breathing after the section of one phrenic with the 

 thoracic breathing before the section of the nerve. 



Do the two sides of the chest move equally, or is there a differ- 

 ence between the right and the left side ? 



3. Stimulate the nerve with single shocks from an inductorium, 

 and take a tracing on the drum. 



4. Enlarge the abdominal opening and pull down the abdom- 

 inal viscera so that the movements of the diaphragm may be ob- 

 served directly. Note the movement of the left side, whose nerve 

 supply is still intact. Note the lack of motion on the right side and 

 the position of this enervated side of the diaphragm during in- 

 spiration and expiration. 



5. Expose and cut the left phrenic nerve. Both sides of the 

 diaphragm are now paralzyed. Note the change in the respira- 

 tory movements. If the rabbit is young there will be great difn- 



[157] 



