210 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. 



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. 93 and 94, 2 (2 6 , ), 

 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 perforate 

 lamina on the base of the brain and the uncinate gyrus. Later 

 there is developed around these primary projections areas what 

 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. 

 95 and 96. 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 2 b , and 14, u b with 7. Later still 

 the great association areas 34, 35, 36, Figs. 95 and 96 acquire 

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

 be considered as association areas with more complex connections, 

 and they serve to mediate therefore the higher psychical activities. 

 Flechsig, in his recent report, designates these areas from an anatom- 

 ical point as terminal or central zones. As the result of his his- 

 tological work, as far as it has progressed, he distinguishes 

 thirty-six areas in the cortex in which the myelinization of the 

 fibers occurs separately, and in which, therefore, by inference, 

 different physiological activities are mediated. These 36 areas 

 are subdivided as follows: 



* 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. 



