674 



THE CEREBRUM 



current. The finer details were brought out subsequently by Ferrier 1 

 by means of faradic stimulation. 



The motor area is situated along the fissure of Rolando (sulcus 

 cruciatus) of each hemisphere and occupies the anterior and posterior 

 central convolutions. Each area is composed of a number of motor 

 points, so-called, because their stimulation with fine electrodes gives 

 rise to contractions of only one particular muscle or group of muscles. 

 In mapping out this field, it is also to be noted that these motor points 

 are arranged in a definite manner, those governing the activity of the 

 muscles of the trunk being situated very close to the longitudinal 

 fissure, and those controlling the posterior extremity upon the upper- 



FIG. 339. LATERAL VIEW OF THE BRAIN OF A 

 DOG. DIAGRAM INDICATING THE LOCATION OF THE 

 MOTOR AREA. 



CS, Crucial sulcus; T, L, A and F, areas for 

 the muscles of the trunk, leg, arm and face. 



FIG. 340. DIAGRAM SHOWING 

 THE MOTOR POINTS IN THE CERE- 

 BRUM OF THE DOG. 



most convexity of the cerebral surface. Directly below this field we 

 find the motor points for the anterior extremity and at a still lower 

 level those for the facial muscles. In general, therefore, it may be 

 stated that each motor area is composed of four minor fields which 

 control respectively the movements of the trunk, leg, arm, and face. 

 Each minor field is subdivided in turn into still smaller ones, the so- 

 called motor points. 



This finer subdivision of the motor areas is not apparent in such 

 mammals as the rabbit, cat, and dog, but becomes unmistakable in the 

 monkeys and reaches its highest development in the apes and man. 

 While only very general reactions can be evoked in rabbits, the cat and 

 dog show movements of a more specialized character. This may be 

 gathered without difficulty from the preceding Fig. 340, illustrating 



1 Les fonctions du cerveau, Paris, 1878. 



