TARSIUS SPECTRUM loi 



gains ill the telenccphalization of vision, the primordial receiving centers 

 for this sense still maintain a high degree of prominence in the midbrain. 

 This primitive feature becomes progressively more prominent in descending 



FIG. 49. DORSAL SURFACE OF BRAIN STEM OF TARSIUS SPECTRUM. 

 [Actual Length, 16 mm.] 



Key to Diagram, dorso-med. fissure, Dorsomedian fissure; d. m. septum, Dorsomcdian Septum; sup. 

 CEREBL. PEDUNCLE, Superior Cerebellar Peduncle; tub. trigem. Tuberculum Trigemini. 



the vertebrate scale to its convergence upon the reptilian basis of mammalian 

 differentiation, at which level it reaches its full expansion in the optic lobes. 



Internal Structure of the Brain Stem 



The impression obtained from a microscopic review of the brain stem is 

 that of a primitive mammalian organization. The structural details are, so to 

 speak, still in the crude. They have none of that refined defmition which dis- 

 tinguishes the higher primates and man. All of the topographical features 



