FUNCTIONAL AREAS OF CORTEX 893 



next to the ependyma of the lateral ventricle. As a mass, they appear in intimate connection 

 with the caudate nucleus, and are spread toward both the frontal and the occipital lobes (chiefly 

 the latter), in the mesial part of the corona radiata of those lobes. It is described as also con- 

 taining fibres in both directions associating the occipital with the temporal lobe. Vertical 

 association fibres pass through the caudate and lenticular nuclei between the cortex above and 

 that of the temporal lobe below. 



(9) Since the olfactory bulb is a part of the hemisphere proper, the olfactory tract may be 

 considered an association pathway connecting the olfactory bulb w^ith the parolfactory area, 

 the subcallosal gyrus, the anterior perforated substance, and the uncus. As already shown, 

 a portion of the fibres of the tract belongs to the commissural system. 



THE FUNCTIONAL AREAS OF THE CEREBRAL CORTEX 



The definitely known areas of specific function of the human cerebral cortex are relatively 

 small. They comprise but little more than a third of the area of the entire hemisphere. They 

 are — (1) the general sensory-motor or somsesthetic area, and (2) the areas for the organs of 

 special sense. They represent portions of the cortex in which terminate sensory or ascending 

 projection fibres bearing impulses from the given peripheral structures, and in which arise motor 

 or descending projection fibres bearing impulses in response. 



Knowledge of the location of the areas has been obtained — (1) by the Flechsig method of 

 investigation, and to a considerable extent by Flechsig himself; (2) from clinico-pathological 

 observations, largely studies of the phenomena resulting from brain tumors and traumatic 

 lesions; (3) by experimental excitation of the cortex of monkeys and apes, the resulting phe- 

 nomena being correlated with the anatomical findings and compared with the observations upon 

 the human brain. The remaining larger and less known areas of the cortex are referred to as 

 'association centres' or areas of the 'higher psychic activities.' 



In development, the sensory fibres to the specific areas acquire their medullary sheaths 

 first, before birth, and then the respective motor fibres from each become meduUated. It is 

 not till a month after birth that the association centres show medullation and therefore acquire 

 active functional connection with the specific areas. 



In defining an area it is not claimed that aU the fibres bearing a given type of impulse 

 terminate in that area, nor that aU the motor fibres leading to the given reaction originate in 

 the area. It can only be said that of the fibres concerned in a given group of reactions, more 

 terminate and arise in the areas cited than in any other areas of the cortex. The corresponding 

 motor fibres arise both in the region of the termination of the sensory fibres (sensory area) 

 and also in a zone (motor area) either partially surrounding or bordering upon a part of the 

 region of termination. 



The different areas are as follows: — 



(1) The somaesthetic (sensory-motor) area, the area of general sensibility, and the area in 

 which arise the larger part of the cerebral motor or pyramidal fibres for the cortical control 

 of the general muscular system. As is to be expected, it is the largest of the specific areas. It 

 includes the anterior central gyrus, posterior central gyrus, the posterior ends of the superior, 

 middle, and inferior frontal gyri, the paracentral lobules, and the immediately adjacent part of 

 the gyrus cinguli. The ascending or sensory fibres are found to terminate most abundantly 

 in the part posterior to the central sulcus (Rolandi), the posterior central g>TUS being the special 

 area of cutaneous sensibilitj^, and the adjacent anterior ends of the horizontal parietal gjTi have 

 been designated as the area of 'muscular sense.' Both these areas are carried over upon the 

 medial surface to involve the lower part of the paracentral lobule and a part of the gyrus cinguU. 

 The anterior central gyrus gives origin to relatively more motor fibres than the other portions of 

 the somsesthetic area. In distribution, the muscles furthest away from the cortex are innervated 

 from the most superior part of the area, the leg area being in the supero-mesial border of the 

 hemisphere, while that from the head is in the anterior and inferior part of the area (fig. 703) . 

 The muscles of mastication and the laryngeal muscles are controlled from the fronto-parietal 

 operculum. Broca's convolution, the opercular portion and part of the triangular portion 

 of the inferior frontal gyrus, of the left hemisphere, constitutes the especial motor area of speech, 

 and Mills has extended this area to include the supero-anterior portion of the insula below. 

 The various authorities differ considerably as to the exact locations of many of the areas for 

 the cortical control of given sets of muscles. Further observations must be skillfully made 

 for localisation of areas of the human cortex in detail and further correlations must be deter- 

 mined between the experiments upon the cortex of anthropoid apes and the functions of that 

 of man. The accompanying diagrams are compiled from several of the diagrams more usually 

 given and must be considered as only approximately correct. 



(2) The visual area. — The especial sensory portion of this area is that immediately border- 

 ing upon either side of the posterior part of the calcarine fissure. The entire area, motor and 

 sensory overlapping each other, includes the whole of the cuneus. The motor visual area proper 

 is described as the more peripheral portion of the entire area. In addition, an area producing 

 eye movements is described as situated in the posterior end of the middle frontal gjTUs. 



(3) The auditory (cochlear) area comprises the middle third of the superior temporal gyrus 

 and the transverse temporal gyri of the temporal operculum. The motor portion of this area 

 lies in its inferior border. The fibres arising in the area course downward in the temporal 

 pontile path to the motor nuclei of the medulla. 



(4) The olfactory area consists of the olfactory trigone, the parolfactory area, the sub- 

 callosal gyrus, part of the anterior perforated substance, the hippocampal gyrus (especially the 

 uncus), and the callosal half of the gyrus cinguh. Its motor or efferent area lies chiefly in the 

 hippocampal gyrus, the fibres from which pass out from the telencephalon by way of the fornix 

 and cingulum. 



