If the fibres coming out from the speech zone be impaired, so that the impulses can not go to the muscles of articulation and breathing, we have Subcortical Motor Aphasia. Its peculiarity is that the person knows perfectly what he wants to say, but yet can not speak the words. He is able to read silently, can understand the speech of others, and can remember music; but, with his inability to speak, he is generally also unable to write or to perform on a musical instrument (yet this last is not always the case). Then we find new variations if his "lesion"--as all kinds of local nervous defects are called--is in the brain centre in the Rolandic region, where arise the memories of the movements required. In this latter case the aphasic patient can readily imitate speech so long as he hears it, can imitate writing so long as it lies before him, but can not do any independent speaking or writing for himself. With this there goes another fact which characterizes this form of aphasia, and which is called Cortical, as opposed to the Subcortical Motor Aphasia described above, that the person may not be able even to think of the words which are appropriate to express his meaning. This is the case when those persons who depend upon the memories of the movements of lip and tongue in their normal speech are injured as described. Besides the two forms of Motor Aphasia now spoken of, there are certain other speech defects which are called Sensory Aphasia. When a lesion occurs in one of the areas of the brain in the speech zone in which the requisite memories of words seen or heard have their seat--as when a ball player is struck over the sight centre in the back of the head--special forms of sensory aphasia show themselves. The ball player will, in this case, have Visual Aphasia, being unable to speak in proportion as he is accustomed in his speaking to depend upon the images of written or printed words. He is quite unable to read or write from a copy which he sees; but he may be able, nevertheless, to write from dictation, and also to repeat words which are spoken to him. This is because in these latter performances he uses his auditory centre, and not the visual. There are, indeed, some persons who are so independent of vision that the loss of the visual centre does not much impair their normal speech. When, again, an injury comes to the auditory centre in the temporal region, we find the converse of the case just described; the defect is then called Auditory Aphasia. The patient can not now speak or write words which he hears, and can not speak spontaneously in proportion as he is accustomed to depend upon his memories of the word sounds. But in most cases he can still both speak and write printed or written words which he sees before him.