RECONSTRUCTION OF CALLITHRIX JACCHUS 187 



mesially and laterally to the descending pallio-pontile and pallio-spinal sys- 

 tems of fibers. These mesial and lateral nuclear masses are connected by 

 relatively light bridges of nuclear material. There is but little evidence 



FIG. 92. DORSAL SURFACE OF THE GRAY MATTER OF THE BRAIN STEM, 

 CALLITHRIX JACCHUS. 

 Key to Diagram, inf. coll., Inferior Colliculus; lat. gen. body. Lateral Geniculate Body; nucl. of 

 BURDACH, Nucleus of Burdach; nucl. of deiters. Nucleus of Deiters; nucl. of coll. Nucleus of GoII; ret. 

 FRM. and RET. form., Reticular Formation; subst. gel. rolando, Substantia Gelatinosa of Rolando; vent, 

 cochl., Ventral Cochlear Nucleus. 



pointing toward the development of the invading strips of nuclear material 

 so richly present in the higher forms. Cephalically the pontile nuclei become 

 continuous with the relatively massive substantia nigra chiefly by means of 

 the mesial and lateral condensations of nuclear material already mentioned 

 in the studv of the brain stem of lemur as the lateral and mesial buttresses. 



The Vestibular Nuclei 



Reconstruction of this mass of nuclear substance discloses a small, 

 wedge-shaped area lying between the nuclei of the columns of Goll and Bur- 



