X PREFACE 



spheres, especially the cerebral cortex. It is doubtless unfortunate that such 

 a condition exists, but an adequate treatise on the neopallium alone would 

 necessitate the addition of at least several vohimes to the present work. 

 The chief emphasis m this description and analysis has been laid upon the 

 brain stem, an element in the cerebrum which has hitherto been too little 

 dwelt upon. In the brain stem are included the medulla oblongata, the 

 cerebellum, the pons Varolii, the midbrain and the interbrain. Even of these 

 parts the more intimate details concerning the structure and evolution of 

 the cerebellum and of the interbrain have not been discussed in extenso. These 

 regions of the primate brain are at present being studied by my colleague. 

 Prof. Henry Alsop Riley, and will shortly appear as separate publications. 



In submitting the brain stem to study, several methods of analysis 

 have been employed. Not only have the gross appearances in this part of 

 the neuraxis been analyzed, but careful microscopic studies of serial sec- 

 tions of the brain have been made at the following critical levels: 



Level of the pyramidal decussation 



Level of the caudal extremity of the dorsal sensory nuclei 



Level of the caudal extremity of the inferior olivary body 



Level through the middle of the inferior olivary body 



Level of the vestibular nuclei 



Level of the cerebellar nuclei 



Level of the inferior portion of the pons Varolii and the emergence 

 of the sixth cranial nerve 



Level through the middle of the pons Varolii 



Level of the emergence of the fourth cranial nerve (nervus trochlearis) 



Level of the inferior colliculus 



Level of the superior colliculus 



Level of the optic chiasm 



Level of the anterior commissure. 



