226 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



would seem to indicate that this portion of the cortex may form 

 a part of the speech area both on the motor and the sensory side. 

 The area is much more developed in man than in the lower mam- 

 mals, and its connections with other parts of the cortex by means 

 of association tracts are such as to lead to the supposition that its 

 general functions are of the higher synthetic character attributed 

 to the association areas in general. 



By way of caution it should be stated that the general ideas developed 

 above in accordance with]Flechsig's views do not meet with universal accept- 

 ance. Some of the most experienced observers are unwilling to admit that 

 such a degree of localization of the psychical activities really exists. They 

 contend that the whole cortex may be concerned in mediating the highest 

 mental processes, and quote post-mortem examinations of carefully studied 

 cases in support of this view. Even in the primary sense centers or motor 

 centers the character of the lamination of the cortex indicates the possibility 

 that the higher synthetic functions may be mediated there in addition to the 

 reception of sensory impulses or the generation of motor impulses. We 

 must recognize, in fact, that the schemata designed to show the distribution of 

 the higher psychical activities in the cortex represent at present only hypotheses 

 which need confirmation before they can be finally accepted. We may feel 

 considerable confidence in the localizations of the motor areas, and of some, at 

 least, of the sensory areas, but in the matter of the more complex mental 

 acts, failure in which expresses itself hi the conditions of aphasia, dementia, 

 perversions, etc., our knowledge is incomplete, both as regards analysis of the 

 symptoms and the localities affected in the brain. 



The Development of the Cortical Area. Flechsig* has 

 published the results of an extensive study of the time of mye- 

 linization of the fibers in the cerebrum of man from the fourth 

 month of intra-uterine to the fourth month of extra-uterine life. 

 The first areas to develop in the cortex are the primary sense 

 centers (smell, cutaneous and muscle sense, sight, hearing, and 

 touch), and later in connection with these centers systems of motor 

 fibers appear. There are thus formed seven primary zones, sensory 

 and motor, to which he gives the name of projection areas. The 

 location of these areas is shown in part in Figs. 98 and 99, 2 ($, &\ 

 5, 6, 7 (7 b ), 8, 15. Two areas connected with the olfactory sense 

 are not shown in these figures; they appear in the anterior per- 

 forate lamina on the base of the brain and in the uncinate gyrus. 

 Later there is developed around these primary zones areas that 

 Flechsig calls marginal or border zones, which have no projection 

 fibers, but which are connected by short association fibers with 

 one or more of the primary projection zones, 14, 16 to 33, in Figs. 

 100 and 101. Later still the great association areas S4, 35, 36, 

 Figs. 100 and 101 acquire their myelinated fibers. These latter 

 centers, as indicated above, may be considered as association areas 



* Flechsig, "Berichte der mathematisch-physischen Klasse der konigl. 

 Sachs. Gesellschaft der Wissenschaften zu Leipzig," 1904. For a summary of 

 the results of this work see Sabin, "The Johns Hopkins Hospital Bulletin,'* 

 February, 1905. 



