216 C. JUDSON HERRICK 



21. The basal forebrain bundle 267 



1) The lateral forebrain bundle 267 



2) The medial forebrain bundle 269 



22. The dorsal tegmental fascicles 270 



23. The ventral tegmental fascicles 271 



24. Tractus tegmento-bulbaris 271 



25. Fasciculus longitudinalis medialis 271 



26. Tractus tegmento-interpeduncularis 272 



V. The commissures of the midbrain and thalamus 273 



VI. Review and discussion of the functional analysis of the midbrain and 



thalamus 279 



The tectum mesencephali 281 



The pars dorsalis thalami 286 



The pars ventralis thalami 289 



The eminentia thalami and tractus cortico-thalamicus 290 



The pedunculus cerebri and motor tegmentum 292 



The nucleus of the tuberculum posterius 294 



The eminentia subcerebellaris tegmenti 296 



The nucleus interpeduncularis 297 



VII. Conclusion 297 



Bibliography 300 



1. INTRODUCTION 



In attacking the problem of the origin and biological signifi- 

 cance of the cerebral cortex comparative neurologists have 

 hitherto generally directed their attention primarily to the 

 cortex itself and its supposed primordia in the lowest vertebrates. 

 As a result of these studies it is becoming increasingly evident 

 that the key to this difficult question is to be sought in the 

 subcortical centers of the primitive types, that is, in the 'old 

 brain' (palaeencephalon of Edinger, segmental apparatus of 

 Adolf Meyer), which attains its definitive pajbtern as a mechan- 

 ism for reflexes and instincts prior in evolutionary history to 

 the emergence of the true cortex (neencephalon, or supraseg- 

 mental apparatus of the forebrain). It is important, therefore, 

 that the exact pattern of these primitive sensori-niotor mechan- 

 isms of the forebrain be determined in advance; for here are 

 to be sought the primary physiological factors through whose 

 interaction the functional pattern of the cerebral hemisphere 

 has been elaborated. 



