CHAPTER III. 



NERVOUS SYSTEM. 



I. REFLEX ACTION. 



CHLOROFORM a frog. Make a longitudinal incision through 

 the skin in the middle line of the skull. Cross this with another 

 incision from ear drum to ear drum. Turn 

 back the skin flaps and expose the skull. 

 Carefully remove this piecemeal with strong 

 scissors and forceps from before backwards. 

 Expose the brain, noting its relations to the 

 landmarks on the skull. Compare with 

 Fig. 18. 



1. Reflex Action with Cerebrum only 

 Removed. Partly anaesthetize a frog. Cut 

 through the skull with sharp scissors or 

 scalpel, transversely, just in front of the ear 

 drums. This will serve to eliminate the 

 cerebral lobes. Clamp the lower jaw in a 

 femur clamp and suspend the frog from an 

 upright stand. Keep the wound made, moist 

 with physiological salt solution. Allow the 

 frog time to recover from the shock of the 

 operation and try the following experiments: 



(a) Immerse one foot in a beaker contain- 

 ing a dilute solution of sulphuric acid (i to 

 10,000). Note the time elapsing between the 

 application of the stimulus and the first muscular contraction. 

 Which muscles contract first? Does the reaction extend to any 



[47] 



9 



FIG. 18. Frog's 

 Brain . i, Olfactory 

 nerves; 2, olfactory 

 lobes ; 3, cerebral lobes ; 

 4, epiphysis cerebri 

 (pineal body) ; 5, optic 

 thalamus ; 6, optic 

 lobes ; 7, cerebellum ; 8, 

 medulla ; 9, rhomboid 

 fossa (fourth ventricle). 



