560 



TEXT-BOOK OF EMBRYOLOGY. 



The general biological significance of this late development of the pallium 

 and especially of its associative mechanisms has already been alluded to. 

 These "added" parts of the nervous system are the most modifiable mechan- 

 isms of the human organism; they are those mechanisms which perform its 

 newest and most highly adaptive adjustments. The other parts of the ner- 

 vous system are fixed at birth, but the cerebral hemispheres are still plastic 

 for the reception and recording of individual experience. Such experience 

 symbolized and formulated (spoken, written, etc.) is transmitted to the next 

 generation, as already pointed out (p. 470). An example of the far-reaching 

 consequences of this capacity of the pallium is the prolonged period of infancy 

 and education of man. 



FIG. 493. Diagram of cortical areas of lateral surface of pallium as determined by the myelogenetic 



'method. Flechsig, from Quain's Anatomy. 

 The numerals indicate, in a general way. the order of myelination. The primary areas (i-io) are 



indicated by dots, the intermediate areas (11-31) by oblique lines and the terminal or final 



areas (32-36) by clear spaces. 



Anomalies. 



Those anomalies of the nervous system involving more general develop- 

 mental anomalies (cyclopia, anencephaly, cranioschisis, spina bifida, etc.) are 

 dealt with in the chapter on Teratogenesis (XIX) . Owing to the fact that the 

 nervous system consists of parts which are more or less separated, and yet con- 

 nected and interdependent, it is in certain respects affected differently from the 

 other organs when portions of it are injured or inhibited in development. Thus 

 an injury or inhibition in development of one part of the nervous system may, 

 because of the dependence upon this part of other perhaps distant parts, affect 

 the development of the latter. Even in the adult, injury of an axone leads to the 



