156 



ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



tions, because it produces a break between the afferent and efferent arcs of the 

 reflex circuits. 



4. Localization of the Reflex Center for the Hind Legs. If the 

 spinal cord has not been destroyed in the frog used for Experiment 3, 

 this animal may now be employed for the following test: Suspend the 

 brainless frog in the usual way. Open its abdominal and thoracic cav- 

 ities and remove the viscera. Identify the vertebral column with its 

 nine vertebrae. Produce a reflex by stimulating the sole of the foot 

 electrically. Now make a transverse cut between the second and third 

 vertebrae. Test the reflexes again. Cut between the third and fourth" 



ON 

 OL 



FIG. 95. DIAGRAMMATIC REPRESENTATION 



OF THE BRAIN OF THE FROG. 

 ON, Olfactory nerves; OL, olfactory 

 lobe; C, cerebrum; T, tween brain; OpL, 

 optic lobes; Ce, cerebellum; M, medulla; 

 Co, spinal cord. The cranial nerves are 

 indicated by Roman numerals. 



FIG. 96. DIAGRAM TO SHOW THE POSI- 

 TION OF THE REFLEX CENTERS IN THE 

 SPINAL CORD OF THE FROG. 



BC and BN, Brachial center and 

 nerve; A, center for the parts of the trunk; 

 SC and SN, sciatic center and nerve. The 

 numbers indicate the different vertebrae. 



vertebrae and again test the reflexes. Continue this process until no 

 longer able to elicit this reflex. At which level do you localize the 

 sciatic center? 



Annotation. The frog possesses nine vertebrae. Its vertebral column ends at 

 the dorsal prominence. From here the tenth vertebra or urostyle extends backward 

 to the tip of the body. Notice that the three roots of the sciatic nerve enter the 

 cord at different levels, the arrangement being such that a transverse cut made 

 between the sixth and seventh vertebrae traverses the upper extent of the sciatic 

 center, destroying the reflexes executed with the help of this nerve. 



5. Localization of Function. The same frog may be used for the 

 following test: Identify the three roots of one sciatic nerve and place 

 them in loose ligatures. Place the frog upon a moistened plate and 

 stimulate each root separately with single induction shocks of very 



