2 QO THE NERVOUS SYSTEM 



at the same time. Much of Flechsig's work has failed to stand the test of rigid 

 examination. It is now known that practically all regions of the cortex, in- 

 cluding those designated by him as association centers, are connected with the 

 thalamus or lower lying centers by afferent or efferent projection fibers. It 

 has been shown that the more mature areas fade off gradually into those whose 

 differentiation is less advanced, and that sharply outlined zones such as are 

 indicated in his figures do not exist. Nevertheless, it is true that the regions 

 designated by him as primary areas, though not sharply outlined by this method 

 from the surrounding cortex, do mature first, and the myelination spreading 

 from these areas reaches its completion last in those areas included in his late 

 group (Brodmann, 1910). The primary areas include the region surrounding 

 the central fissure, the region around the calcarine fissure, a portion of the 

 superior temporal gyrus, and a part of the hippocampal gyrus. These areas 

 are associated with especially important projection tracts and may properly 

 be spoken of as projection centers. 



CORTICAL OR CEREBRAL LOCALIZATION 



In opposition to the crude conceptions of the localization of cerebral functions 

 introduced by Gall (1825), which formed the basis for phrenology, the French 

 physiologist Florens maintained the doctrine that all parts of the cerebrum are 

 functionally equivalent. In 1861 Broca demonstrated that destruction of the 

 left third frontal convolution may result in a loss of ability to speak; and nine 

 years later Fritsch and Hitzig (1870) discovered that electric excitation of the 

 cortex in the region of the central sulcus will elicit movements from muscles of 

 the opposite side of the body. These observations, confirmed and extended 

 by many observers, definitely proved that certain cortical areas possess spe- 

 cialized functions. Physiologic and pathologic researches have served to out- 

 line a number of these with considerable precision, and it is possible to identify 

 them with regions of characteristic cell and fiber lamination. In this way evi- 

 dence derived from histologic studies reinforces that drawn from physiology and 

 pathology. 



The motor projection center is located in the anterior -wall of the central sulcus, 

 in the adjacent part of the anterior central gyrus, and in that part of the para- 

 central lobule which lies rostral to the continuation of the central sulcus on the 

 medial surface of the hemisphere (Figs. 220, 221). It coincides fairly closely 

 with Area 4 of Brodmann's charts (Figs. 216, 217). This is the center from which 

 the impulses initiating voluntary movements on the opposite side of the body 





