LESSON X. SOME ACTIONS OF THE SPINAL CORD. 



A. Lymph-Hearts. Reflex Action. 



1 . A frog is given you in which the brain but not the 

 spinal cord has been destroyed 1 . Placing the animal on 

 its belly, watch the movements of the posterior lymph- 

 hearts. They may be seen beating on either side of the 

 extremity of the urostyle, in a depression between that 

 bone and the hip-joint. 



The beat of the posterior lymph-hearts is due to nerve 

 impulses proceeding from the spinal cord by the 10th 

 spinal nerve. After the destruction of the spinal cord in 

 16, note that the lymph-hearts no longer beat. 



2. Place the frog in a sitting posture. Observe that 

 its hind-limbs are drawn up under the body ; but that it 

 differs from the normal frog in the following respects. 



Its head is depressed, instead of being erect. 



Its fore-limbs are spread out, or flexed, instead of 

 being held nearly vertical; thus the angle which the 

 body makes with the table is diminished. 



There are no respiratory movements, either of the 

 nostrils or of the throat. 



3. Gently pull out one of the hind-limbs, until it be- 

 comes quite straight, and then let it go. It will be im- 

 mediately drawn up into its old position under the body. 



1 The nervous structures in the skull and in the canal of the 1st verte- 

 bra are destroyed with a seeker. If the latter part is not destroyed, a 

 part of the spinal bulb is left and the reflexes are more complex than 

 with the spinal cord alone. 



