7io 



POSITION OF THE MOTOU CENTRES. 



these, whether they affect the general or localised areas, give rise to unilateral con- 

 volutions and monospasm respectively. 



Monospasm According to the seat of the spasm, it is called facial, brachial, crural mono- 

 simsm, fcc. Of coarse these spasms may affect several groups of muscles. Bartholow and 

 S. iainanna have stimulated the exi>osed human brain successfully with electricity. 



Cerebral Epilepsy. Very powerful stimulation of one side may give rise to 

 bilateral spasms, with loss of consciousness. In this case, < impulses are conducted 

 to the other hemisphere by commissural fibres ( 379). 



Movements of the Eye. Nothing definite is known regarding the centre in the cortex for 

 voluntary eambint ' mou ments of the eyeballs in man. In paralytic affections of the cortex and 

 of the paths proceeding from it, we occasionally find both eyes with a lateral deviation. If the 

 paralytic affection lies in one cerebral hemisphere, the conjugate deviation of the eyeballs is 

 towards the sound side (p. 588). If it is situated in the conducting paths, after these have 

 decussated, viz., in the pons, the eyes are turned towards the paralysed side (Prevost). 



If the part be irritated so as to produce spasms in the opposite half of the body, of course the 

 eyes are turned in the direction opposite to that in pure paralysis. Instead of the lateral 

 deviation of the eyeballs already described, there is occasionally in cerebral paralysis merely a 

 weakening of the lateral recti muscles, so that during rest the eyes are not yet turned towards 

 the sound side, but they cannot be turned strongly towards the affected side {Leichtcnstern, 

 Sunnius). The centre for the levator palpebral superioris appears to be placed in the angular 

 gyrus (Grassct, Landouzy). 



II. The Centre for Speech. The investigations of Bouilland [1825], Dax 

 [1836], Broca [1SG1], Kussmaul, Broadbent, and others have shown that the third 

 left frontal convolution of the cerebrum (figs. 484, F3, and 488) is of essential 

 importance for speech, while probably the island of Reil also is concerned. The 

 island is deeply placed, and is seen on lifting up the overhanging part of the brain 

 called the operculum, lying between the two branches of the Sylvian fissure (S). 

 The motor centres for the organs of speech (lips, tongue) lie in this region, and 

 here also the psychical processes in the act of speech are completed. In the great 

 majority of mankind, the centre for speech is located in the left hemisphere. The 

 fact that most men are right-handed also points to a finer construction of the motor 

 apparatus for the upper extremity, which must also be located in the left hemisphere. 

 Men, therefore, with pronounced right-handedness (" droiters ") are evidently left- 

 brained (" gauchers du cerveau " Broca). By far the greater number of mankind 

 are "left-brained speakers 11 (Kussmaul) ; still there are exceptions. As a matter 

 of fact, cases have been observed of left-handed persons who lost their power of 

 speech after a lesion of the right hemisphere (Ogle). Investigations on the brains 

 of remarkable men have shown that in them the third frontal convolution is more 

 extensive and more complex than in men of a lower mental calibre. In deaf-mutes 

 it is very simple ; microcephales and monkeys possess only a rudimentary third 

 frontal (Riidinger). 



The motor tract for speech passes along the upper edge of the island'of Reil, then into the 

 substance of the hemispheres internal to the posterior edge of the knee of the internal capsule ; 

 from thence, through the crusta of the left cerebral peduncle into the left half of the pons, 

 where it crosses, then into the medulla oblongata, which is the place where all the motor nerves 

 (trigeminus, facial, hypoglossal, vagus, and the respiratory nerves) concerned in speech arise. 

 Total destruction of these paths, therefore, causes total aphasia ; while partial destruction 

 causes a greater or less disturbance of the mechanism of articulation, which has been called 

 "anarthna" by Leyden and Wernicke. 



Condition;. Three activities are required for speech (1) the normal movement 

 of the vocal apparatus (tongue, lips, mouth, and respiratory apparatus) ; (2) a 

 knowledge of the signs for objects and ideas (oral, written and imitative or mimetic 

 signs) ; (3) the correct union of both. 



Aphasia (d priv. and <f>da-i<s speech). Injury of the speech-centre causes either a 

 loss or more or less considerable disturbance of the power of speech. The loss of 

 the power of speech is called "aphasia:' [Aphasia, as usually understood, means 

 the partial or complete loss of the power of articulate speech from cerebral causes.] 



