212 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



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 accep- 

 tance. 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. 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 satisfactory con- 

 firmation 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 in 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 Areas. In a recent report 

 Flechsig* gives the results of an extensive study of the time of 

 myelinization 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. 92 and 93, 2 ($, &}, 

 5, 6, 7 (7 6 ), 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 gyms. 

 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. 

 94 and 95. These areas all develop after birth; and from a 

 physiological standpoint may be regarded perhaps as the seat of 

 the organized memories connected with the primary sense centers. 

 It is injuries in these centers which may be supposed to produce 

 the various kinds of aphasia described above. Thus, areas 17, 20, 

 and 24 form border areas to the primary area of sight (5); 16 has 

 the same relation to 2, 18 to /, and 14, U b with 7. Later still 

 the great association areas 34, 35, 36, Figs. 94 and 95 acquire 

 their myelinated fibers. These latter centers, as indicated above, may 



* 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. 



