796 PHYSIOLOGICAL TOPOGRAPHY OF SURFACE OF CEREBRUM. 



form than in the brains from persons of lower grade of intelligence. In 

 deaf-mutes this convolution is exceedingly simple and in microcephalic 

 fetuses and in apes it is merely rudimentary. 



Injuries of this speech-center, as well as transitory functional dis- 

 orders, for example in consequence of copious hemorrhage, are followed 

 either by loss or at least by more or less considerable derangement of 

 the faculty of speech. The loss of the faculty of speech is designated 

 aphasia. Stimulation of this region causes sensations of speech-movement, 

 which occur rarely, the sensations often being referred by the patients, 

 for example paralytics, to other parts of the body. 



FIG. 262. View of the Median Surface of the Human Brain: CC, the divided corpus callosum; F', first frontal 

 convolution continuous at a with the anterior central convolution 04); B, posterior central convolution; 

 between A and B is the median extremity of the fissure of Rolando (AB designated paracentral lobule); Gf, 

 gyrus fornicatus, bounded by the callosomarginal fissure (cm} from the first frontal and the central convolu- 

 tions. The callosomarginal fissure (cm in Fig. 260) passes upward between B and P (the superior parietal 

 lobule); po, the parieto-occipito fissure (po in Fig. 260) separates the occipital lobe (O) from the parietal 

 lobe (P); Q, quadrate lobe (precuneus); Cu, cuneus; cc, calcarine fissure; Lg, lingual lobe (median occipito- 

 temporal gyrus); Fs, fusiform lobule (lateral occipito-temporal gyrus); H, hippocampal gyrus; U, uncinate 

 gyrus; h, hippocampal sulcus; F, frontal, P, parietal, O, occipital lobe. 



The motor .tract for speech passes from the third frontal convolution first along 

 the upper margin of the island of Reil, then in the depth of the hemisphere in- 

 ternally to the posterior margin of the lenticular nucleus, and then through the 

 crusta of the left cerebral peduncle and the left half of the pons to the medulla 

 oblongata, the seat of the nuclei of all the motor nerves concerned in the act of 

 speaking trigeminus, facial, hypoglossus, vagus, respiratory nerves. Total 

 destruction of this motor tract causes, therefore, total aphasia. Partial lesions 

 cause more or less coarse derangement of the mechanism of articulation, which 

 has been designated anarthria. 



Three types of activity are necessary for the function of speech : i . 

 The normal movement of the speech-apparatus tongue, lips, mouth, 

 respiratory apparatus. 2. A knowledge of the symbols for objects and 

 ideas speech, writing, and gesture. 3. The correct association of the 

 two. Therefore, the following essentially different forms of aphasia 

 must be distinguished: 



