26 



THE FROG 



Make a diagram of the central nervous system and indicate what 

 parts have been present in each of the specimens used. Also make 

 a diagram of a cross section of the spinal cord through the roots of a 



dorsa/ root 



white matter 



gray matter 



efferent 

 neuron 



dorsa/ root 

 nglion 



afferent 

 neuroo 



efferent neuron 



dorja/ root 

 gonq//on 



I 



^ afferent 

 ■neurons 



dorsaf root 



effector receptor 



Fig. 24. — A, the spinal cord, in cross section, showing a pair of spinal nerves 

 and the essential parts of a reflex arc; diagrammatic. The neurons necessary 

 for the simplest type of reflex action are present on the left, while those of 

 a typical reflex arc are represented on the right. B, the spinal cord showing 

 some relations of neurons in reflex arcs; diagrammatic. The brain would 

 he to the right as the diagram is constructed. Arrows in both diagrams 

 indicate the direction of transmission of the nervous impulses. 



pair of spinal nerves and show the positions of the neurons of a typical 

 reflex arc (c/. Fig. 24). On the basis of your observations, write 

 out statements of the functions localized (1) in the sense organs, (2) 

 in the peripheral nervous system, (3) in the spinal cord, (4) in the 



