396 MUSCULAR ACTION 



relations of the speech-center with other aspects of body and of mind 

 we can as yet but guess about. Here in especial degree hypotheses 

 are vain, so far apart in character are an idea and the moving parts 

 which express it. 



The chief nerve-trunks containing fibers concerned in speech and 

 respiration have already been mentioned. The larynx is supplied by 

 the superior laryngeal and by the inferior or recurrent laryngeal branches 

 of the vagus. The other nerves vitally concerned in speech are prac- 

 tically those of deglutition and of mastication. 



The speech-center in the child, according to Gowers, like most centers, 

 is probably bilateral, but it gradually builds most of its connections into 

 the left hemisphere. Whether or not the common and unfortunate 

 development of one-sided hand-function, "right-handedness," is the 

 cause of this unilateral location of the speech-center is as yet not known. 

 More likely than not, however, this is the reason of it. In left-handed 

 persons the center is in the right hemisphere. There is considerable 

 evidence that in childhood or later if one speech-center area be destroyed 

 the same region of the opposite hemisphere may take up its function of 

 remembering the motor ideas, etc., of speech. We have seen above 

 that the real motor-center of the vocal process is in the ambiguous 

 nucleus of the vagus, the influence coming to it (by way of the spinal 

 accessory?) from some part of the cortex cerebri above by some road as 

 yet not sure. By its association-powers this knot of fibers wherever it be 

 placed in the cortex, over-sees or perhaps controls the more mechanical 

 and truly motor centers in the cerebellum, medulla, or cord, it contains 

 the kinesthetic traces used in articulating words. 



The exact location of this supervising associating center in the cortex 

 was determined by Broca following up valuable work by Bouilland, who 

 in turn was inspired (Howell) by the work of the famous pre-scientific 

 phrenologist Goll. It is seated undoubtedly in the third or lower frontal 

 convolution in the region surrounding the short anterior vertical branch 

 of the fissure of Sylvius. In this area of four or five square centimeters 

 of knotted neurones are somehow stored and associated the kines- 

 thetic directions for moving the speech-organs via other centers in the 

 medulla. It is to be noted that this center is part of the so-called 

 "motor area" of the brain, or at least it is close to the region representing 

 all movements of the neck, face, and mouth. Just below this area, on 

 the other side of the Sylvian fissure in the superior gyrus of the temporal 

 lobe are traced the memories of the word-symbols themselves in their 

 relations to the senses and other yet more purely psychical conditions. 

 From this former region the motor fibers extend deeply inward to the 

 posterior part of the lenticular nucleus and then downward to the 

 medulla as above mentioned. 



APHASIA. The various kinds of aphasia are practically important 

 sometimes for locating cerebral disease, and theoretically of great interest 

 because of the light they throw on the psychomotor apparatus of speech 

 and of language. They are varieties of speech-defect corresponding to 



