144 HUMAN PHYSIOLOGY. 



mined by these observers will be readily understood by an examination of 

 Figures 17 and 18. 



For diagnostic purposes the motor areas for the face and limbs have been 

 subdivided as follows : 



1. The face area may be divided into an upper part comprising about 

 one-third, and a lower part comprising the remaining two-thirds. In the 

 upper part are centres governing the movements of the muscles of the oppo- 

 site angle of the mouth and of the lower face. The anterior portion of the 

 lower two-thirds controls the movements of the vocal cords and may be 

 regarded as a laryngeal centre; the posterior portion governs the opening 

 and shutting of the mouth and the protrusion and retraction of the tongue. 



2. The upper limb area may be subdivided as follows : The upper part 



FIG. 17. 



DIAGRAM OF THE MOTOR AREAS ON THE OUTER SURFACE OF A MONKEY S BRAIN. 



Horsley and Schafer. 



controls the movements of the shoulder; posterior and below this point are 

 centres for the elbow ; below and anteriorly, centres for the wrist and finger 

 movements, while lowest and posteriorly centres governing the thumb. 



3. The leg area may be subdivided as follows : The anterior part, both 

 on the mesial and lateral surfaces, contains centres governing the hip and 

 thigh movements; in the posterior part are centres for the movements of 

 the leg and toes. The centre for the big toe has been located in the para- 

 central lobule. 



4. The trunk area, situated largely on the mesial surface, contains 

 anteriorly centres governing the rotation and arching of the spine, while 

 posteriorly are found centres governing movements of the tail and pelvis. 



5. The head area, or area for visual direction, contains centres, excita- 



