1899.] on Structure of the Brain in Relation to its Functions. 131 



projection systems the neurones are arranged in series, and that a 

 sensation coming from the skin before it reaches the surface of the 

 brain has to pass through a series of three neurones which are in 

 physiological connection with one another, and the consciousness of 

 the skin perception depends upon the intensity of the stimulus and 

 the conducting capacity of the chain of nervous elements. You will 



* Association Systoit 



Efferent 



Projection 



System 



CorJ>. Striata 



Fig. 8. 



Diagram to show the Three Systems of Neurones, illustrating the path of 

 sensory impulses to the Cerebrum and Cerebellum, the path of outgoing im- 

 pulses from the Brain in a voluntary movement and the association of the 

 afferent and efferent projection systems in the grey matter of the Brain. This 

 diagram also illustrates the path of a simple spinal reflex and of a psychical 

 reflex. 



observe at right angles to the ingoing and outgoing fibres there are 

 other fibres which join up these systems serving to coordinate tho 

 nervous currents arriving at and leaving this area of the brain : these 

 are association fibres, so that if a skin sensation excites a conscious 

 volitional movement, this will be the path of the nervous current. 



If, however, we move our hand in response to some visual sensa- 

 tion, it is obvious that long association systems of neurones must 



K 2 



