Gall, the founder of the doctrine of Phrenology, wrecked his fame as a scientist by associating mental faculties with conditions of the skull instead of conditions of the brain beneath; nevertheless, he deserves the highest credit for his discoveries and deductions, for he was the first to point out that that part of the brain with which psychic processes are connected must be the cerebral hemispheres. He said, if we compare man with animals we find that the sensory functions of animals are much finer and more highly developed than in man; in man, on the other hand, we find intelligence much more highly developed than in animals. Upon comparing the corresponding anatomical conditions, we see, he said, that in animals the deeper situated parts of the brain are relatively more developed and the hemispheres less developed than in man; in man, the hemispheres so surpass in development those of animals that we [!-- pagenumber --]can find no analogy. Gall therefore argued that we must consider the cerebral hemispheres to be the seat of the higher functions of the mind. We must moreover acknowledge that the following deductions of Gall are quite sound: "The convolutions ought to be recognised as the parts where the instincts, feelings, thoughts, talents, the affective qualities in general, and the moral and intellectual forces are exercised." The Paris Academy of Science appointed a commission of inquiry, May, 1808, which declared the doctrine of Gall to be erroneous. Gall moreover surmised that the faculty of language lay in the frontal lobes, and Bouillaud supported Gall's proposition by citing cases in which speech had been affected during life, and in which after death the frontal lobes were found to be damaged by disease. A great controversy ensued in France; popular imagination was stirred up especially in the republic by the doctrine of Gall, which was an attempt to materialise and localise psychic processes. Unfortunately Gall's imagination, encouraged by a widespread wave of popular sympathy, overstepped his judgment and launched him into speculative hypotheses unsupported by facts. His doctrine of Phrenology was shown to be absolutely illogical; [!-- pagenumber --]consequently it was forgotten that he was the pioneer of cerebral localisation.
SPEECH AND RIGHT-HANDEDNESS
The next step in Cerebral Localisation was made by a French physician, Marc Dax, who first observed that disease of the left half of the cerebrum producing paralysis of the right half of the body (right hemiplegia) was associated with loss of articulate speech. This observation led to the establishment of a most important fact in connection with speech, viz. that right-handed people use their left cerebral hemisphere as the executive portion of the brain in speech. Subsequently it was shown that when left-handed people were paralysed on the left side by disease of the right hemisphere, they lost their powers of speech. But the great majority of people are born right-handed, consequently the right hand being especially the instrument of the mind in the majority of people, the left hemisphere is the leading hemisphere; and since probably specialisation of function of the right hand (dexterity) has been so closely associated with that other instrument of the mind, the vocal instrument of articulate speech, the two have now become inseparable; for are not graphic signs and verbal signs intimately [!-- pagenumber --]interwoven in the development of language and human intelligence?
What has determined the predominance of the left hemisphere in speech? I can find no adequate anatomical explanation. There is no difference in weight of the two hemispheres in normal brains. Moreover, I am unable to subscribe to the opinion that there is any evidence to show that the left hemisphere receives a larger supply of blood than the right. Another theory advanced to explain localisation of speech and right-handedness in the left hemisphere is that the heavier organs, lung and liver, being on the right side have determined a mechanical advantage which has led to right-handedness in the great majority of people. This theory has, however, been disposed of by the fact that cases in which there has been a complete transposition of the viscera have not been left-handed in a larger proportion of cases. The great majority of people, modern and ancient, civilised and uncivilised, use the right hand by preference. Even graphic representations on the sun-baked clay records of Assyria, and the drawings on rocks, tusks, and horns of animals of the flint-weapon men of prehistoric times show that man was then right-handed. There is a difference of opinion whether anthropoid [!-- pagenumber --]apes use the right hand in preference to the left. Professor Cunningham, who made a special study of this subject, asserts that they use either hand indifferently; so also does the infant at first, and the idiot in a considerable number of cases. Then why should man, even primitive, have chosen the right hand as the instrument of the mind? Seeing that there is no apparent anatomical reason, we may ask ourselves the question: Is it the result of an acquired useful habit to which anatomical conditions may subsequently have contributed as a co-efficient? Primitive man depended largely upon gesture language, and the placing of the hand over the heart is universally understood to signify love and fidelity. Uneducated deaf mutes, whose only means of communicating with their fellow-men is by gestures, not only use this sign, but imply hatred also by holding the hand over the heart accompanied by the sign of negation. Moreover, pointing to the heart accompanied by a cry of pain or joy would indicate respectively death of an enemy or friend. Again, primitive man protected himself from the weapons of his enemies by holding the shield in his left hand, thus covering the heart and leaving the right hand free to wield his spear. The [!-- pagenumber --]question whether it would have been to his advantage to use either hand indifferently for spear and shield has been, to my mind, solved by the fact that in the long procession of ages evolution has determined right-handed specialisation as being more advantageous to the progress of mankind than ambidexterity. Right-handedness is an inherited character in the same sense as the potential power of speech.
LOCALISATION OF SPEECH CENTRES IN THE BRAIN
In 1863 Broca showed the importance in all right-handed people (that is in about ninety-five per cent of all human beings) of the third left frontal convolution for speech (vide figs. [16] and [17]); when this is destroyed by disease, although the patient can understand what is said and can understand written and printed language, the power of articulate speech is lost. Motor Aphasia. This portion of the brain is concerned with the revival of the motor images, and has been termed by Dr. Bastian "the glosso-kinæsthetic centre," or the cortical grey matter, in which the images of the sense of movement of the lips and tongue are formed (vide [fig. 17]). A destruction of a similar portion of the cortex in a right-handed person produces [!-- pagenumber --]no loss of speech; but if the person is left-handed there is aphasia, because he, being left-handed, uses the third right inferior frontal convolution for speech. These facts have for long been accepted by most neurologists, but recently doubts have been cast upon this fundamental principle of cerebral localisation by a most distinguished French neurologist, M. Marie; he has pointed out that a destructive lesion of the cortex may be accompanied by subcortical damage, which interrupts fibres coming from other parts of the brain connected with speech.
In the study of speech defects it is useful to employ a diagram; a certain part of the brain corresponds to the Speech Zone there indicated, and lesions injuring any part of this area in the left hemisphere cause speech defects (vide [fig. 17]). All neurologists, M. Marie included, admit this, and the whole question therefore is: Is a destruction of certain limited regions of the superficial grey matter the cause of different forms of speech defects, or are they not due more to the destruction of subcortical systems of fibres, which lie beneath this cortical speech zone?
There is a certain portion of the speech zone which is assumed to be connected with the revival of written or printed [!-- pagenumber --]language, and is called the visual word-centre. There is another region connected with the memory of spoken words—the auditory word-centre; you will observe that it is situated in the posterior third of the first temporal convolution, but this does not [!-- pagenumber --]comprise nearly the whole of it, for there is an extensive surface of grey matter lying unseen within the fissure, called the transverse convolutions, or gyri. Lesions of either of these regions give rise to Sensory Aphasia, which means a loss of speech due to inability to revive in memory the articulate sounds which serve as verbal symbols, or the graphic signs which serve as visual symbols for language.