550 TEXT-BOOK OF PHYSIOLOGY. 



while the area for peripheral vision is in the posterior portion of the mesial 

 surface and for a variable distance on the outer surface. Moreover, there 

 is reason to believe that the area for macular vision is in relation with homony- 

 mous halves of the two maculae luteae. The supposed error, the assignment 

 of macular vision to the angular gyrus, has been attributed to destruction of 

 the fibers of the optic radiation, which in their course to the occipital lobe 

 pass close to this gyrus. 



The Motor Areas of the Monkey Brain. From experiments made on 

 the brains of monkeys Ferrier mapped out a number of areas stimulation of 

 which give rise to muscle contractions on the opposite side of the body which 

 are so purposive and coordinate in character that they may be regarded as 

 identical with those produced volitionally. Destruction of these areas is 

 followed by paralysis. Collectively these areas are known as the motor area 

 or motor zone; and as it is ranged along the Rolandic fissure, it is sometimes 

 termed the Rolandic area. 



The experiments of Horsley and Schafer added additional facts and 

 enabled them to construct a new diagrammatic representation of the motor 

 area and more accurately define the special areas upon the lateral and mesial 

 aspects of the brain of the monkey. The boundaries of the general and 

 special areas, as determined by these observers, will be readily apparent 

 from an examination of Fig. 250. Their experiments have enabled them 

 also to subdivide the general into special areas as follows: 



1. The head area or area for visual direction into areas excitation of which 



causes " opening of the eyes, dilatation of the pupils and turning the 

 head to the opposite side with conjugate deviation of the eyes to that 

 side." 



2. The leg area may be subdivided into (a) an area both on the lateral and 



mesial surfaces which presides over the movements of the hip and 

 thigh; (b) an area in the posterior part which presides over the move- 

 ments of the legs and toes; (c) an area in the paracentral lobule for the 

 movements of the hallux or great toe. 



3. The trunk area, situated largely on the mesial surface, may be subdivided 



into an anterior and a posterior area, which respectively preside over 

 the movements of the spinal column as arching and rotation, and the 

 movements of the pelvis and tail. 



4. The arm area may be subdivided as follows: (a) an area superiorly 



which controls the movements of the shoulder; (b) an area posteriorly 

 and below this, which controls the movements of the elbow; (c) an 

 area anteriorly and below the preceding, governing the movements of 

 the wrist and fingers; (d) an area posteriorly and below governing the 

 movements of the thumb. 



5. 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 areas governing the movements of the opposite angle 

 of the mouth and of the lower face. In the lower part anteriorly there 

 is an area governing the movements of the vocal membranes or bands 

 (the laryngeal area); posteriorly areas governing the opening and 

 closing of the mouth, the protrusion and retraction of the tongue. 



