THE NERVOUS SYSTEM 



221 



ing ends of the axon and transmitted to the cell body. In other 

 neurons the stimulus is received by the dendrites and trans- 

 mitted from these to the cell body and thence on through the 

 axon. The connection between a neuron and an effector is by 

 means of the branching ends of either the axon or the dendrite. 



Pigeon 



Dog 



Monkey 



Man 



Fig. 112. Brains of vertebrates 



Note the relative size of the cerebellum in the bird and mammals. In the mammals 

 note the great increase of cerebrum and the increasing amount of convolution, or 

 wrinkling, of the brain surface. The greater brain area in the higher animals corre- 

 sponds to greater numbers of association neurons, and thus to greater intelligence 



181. Kinds of neurons. Four types of neurons have been 

 recognized, classified according to their behavior. 



1. Neurons that transmit impulses toward the brain or spinal 

 cord. These are called the afferent (bearing toward) or sensory 

 neurons, because so many of them are connected with the sense 

 organs on the surface of the body. 



2. Those that carry impidses from the cord or brain — the 

 efferent (bearing out) neurons. These may stimulate muscles 

 or glands (see Fig. in). 



3. Those that connect afferent and efferent neurons. These 

 may be called associative neurons. 



