AMPHIBIA. 



217 



cation of stimuli. They are also the seat of consciousness and 

 intelligence. 



The cranio-spinal nerves are made up of afferent and efferent 

 fibres, of which either or both may occur in the same nerve. The 

 preceding table exhibits the leading features of the cranial nerves. 



All the spinal nerves are of mixed character, the fibres derived 

 from the dorsal roots being sensory, those from the ventral roots 

 motor. The sensory-fibres supply the skin, the motor the 

 voluntary muscles of the body ; in the case of the hypoglossal 

 some of those belonging to the tongue. The preceding facts 

 have been ascertained by cutting the roots and stimulating 

 the ends, it being remembered that fibres only carry impulses 

 one way, and hence no demonstrable results follow on stimulating 

 the peripheral ends of sensory, or the central ends of motor, fibres. 



Therefore, the fibres of the dorsal root are sensory, those of 

 the ventral, motor. (See next page.) 



The sympathetic system supplies and largely regulates the 

 internal organs. By its means involuntary muscular contrac- 



