POSITION OF THE MOTOR CENTRES IN THE DOG. 695 



convolution (IV) bounds the longitudinal fissure, and is separated from its fellow of the opposite 

 side by the falx cerebri ; anteriorly.it embraces the sulcus cruciatus (S), so that it is divided 

 into two parts by this sulcus, a part, the gyrus prsecruciatus or prsefrontalis, lying in front of 

 the sulcus, and the gyrus postcruciatus (postfrontalis) lying behind it. The third primary con- 

 volution (III) runs parallel to the fourth. Some authors count the convolutions from the 

 longitudinal fissure outwards. In fig. 483, I and II, the motor areas or centres are indicated 

 by dots on the individual primary convolutions. We must remember, however, that the 

 centres are not mere points, but that they vary in size from that of a pea upwards, according to 

 the size of the animal. Motor areas have been mapped out in the brain of the monkey, rabbit, 

 rat, bird, and frog. 



Position of the Motor Centres (Dog). Fritsch and Hitzig, in 1870, mapped out the following 

 motor areas, whose position may be readily found on referring to fig. 483 : 1, is the centre for 

 the muscles of the neck ; 2, for the extensors and adductors of the fore limb ; 3, for the flexion 

 and rotation of the fore leg ; 4, for the movements of the hind limb, which Luciani and 

 Tamburini resolved into two antagonistic centres ; 5, for the muscles of the face, or the facial 

 centre. In 1873 Ferrier discovered the following additional centres : 6, for the lateral switch- 

 ing movements of the tail; 7, for the retraction and abduction of the fore limb ; 8, for the 

 elevation of the shoulder and extension of the fore limb, as in walking ; the area marked 

 9, 9, 9, controls the movements of the orbicularis palpebrarum, and of the zygomaticus (closure 

 of the eyelids), together with the upward movement of the eyeball and narrowing of the pupil. 

 Stimulation of the areas a, a (fig. II) is followed by retraction and elevation of the angle of 

 the mouth, with partial opening of the mouth ; at b, Ferrier observed opening of the mouth 

 with protrusion and retraction of the tongue, while the dog not unfrequently howled. He 

 called this centre the "oral centre." Stimulation of c c causes retraction of the angle of the 

 mouth, owing to the action of the platysma, while c' causes elevation of the angle of the mouth 

 and of one-half of the face, until the eye may be closed, just as in 9. Stimulation of d is 

 followed by opening of the eye and dilatation of the pupil, while the eyes and head are turned 

 towards the other side. According to H. Munk, the prefrontal region has an influence upon 

 the attitude of the body (?}. The perineal muscles contract when the gyrus postcruciatus is 

 stimulated. Stimulation of the gyrus prsecruciatus on its anterior and sloping aspect causes 

 movements in the pharynx and larynx. 



The position of the individual motor areas may vary somewhat, and they may be 

 slightly different on the two sides [Luciani and Tamburini). 



Strong" Stimuli. If the stimulation be very strong, not only the muscles on 

 the opposite side, but those on the same side, may contract. These latter move- 

 ments belong to the class of associated movements, and are due to conduction 

 through commissural fibres. Those muscles, which usually (muscles of mastication) 

 or always (muscles of eye, larynx, and face) act together, appear to have a centre 

 not only in the opposite but also in the hemisphere of the same side (Exner). [All 

 observers have found that stimulation of the facial centre causes identical (associated) 

 movements on both sides of the face, so that both sides of the face seem to be 

 represented in each hemisphere. Schafer and Horsley's experiments make it very 

 probable that some other muscles, e.g., some of the trunk muscles, pectorals, and 

 recti abdominis, are represented bilaterally in the hemispheres. This is an 

 important point; in relation to recovery after the supposed destruction of a centre, 

 and has an intimate bearing on the question of " Substitution," in reference to the 

 restoration of nerve-function (p. 682).] 



Mechanical stimulation, e.g., scraping the motor areas for the limbs, produces 

 movements in these parts {Luciani). 



Cerebral Epilepsy. It is of great practical diagnostic importance to ascertain if 

 stimulation of the motor areas in man, due to local diseases (inflammation, tumours, 

 softening, degenerative irritation), causes movements. [Hughlings-Jackson has 

 shown that local diseases of the cortex may cause spasmodic contractions in certain 

 groups of muscles, a condition known as " Jacksonian Epilepsy," and he explains 

 in this way the occurrence of unilateral local epileptiform spasms, which were 

 observed by Ferrier and Landois to occur after inflammatory irritation.] Luciani 

 observed these spasms in dogs, and sometimes they were so violent and general as 

 to constitute an attack of epilepsy. This condition became hereditary, and the 

 animals ultimately died from epilepsy ( 373). According to Eckhard, epileptic 



