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PHYSIOLOGY FOR DENTAL STUDENTS. 



(p. 248), and thus connect with the anterior horn cells of tlic 

 spinal cord. 



In the Rolandic area, as it is called, is therefore situated the 

 cerebral link in the chain of neurones (see p. 249) through 

 which the ordinary movements of the body take place. Such 

 movements may be set agoing, either by stimulation of the 

 Rolandic nerve cells through afferent fibers a pure reflex or 

 by impulses coming to them from the centers of volition situated 



Fig. 50. Cortical centers in man. Of the three shaded areas bordering on 

 the Rolandic fissure (Rol.) , the most anterior is the precentral associatiunul 

 area, the middle one is the motor area (the position of the body areas are 

 indicated on it), and the most posterior is the sensory area, to the cells of 

 which the fillet fibers proceed. The centers for seeing and hearing are also 

 shown. The unshaded portion in front of the Rolandic area is the precentral ; 

 the portions behind, the parietal and temperosphenoidal. 



in the prefrontal convolutions. Or, again, the nerve cell, at the 

 same time that it receives a sensory impulse coming up from 

 the spinal cord, may receive one from the prefrontal convolu- 

 tions which may either interdict or greatly modify the reflex 

 response. Every possible muscular group in the body has a 

 center of its own in the Rolandic area, the determination of the 

 exact location of these centers being one of the achievements 

 of modern medical science. Thus, if we stimulate with a finely 



