CHAPTER VI 

 CORPUS STRIATUM OF MAMMALS 



There are^ as I look at it^ only two roads which can lead 

 to the understanding of the structure of the brain^ though 

 these have been but little travelled up till now. These two roads 

 are comparative anatomy and the anatomy of the foetus^ which 

 should guide us here like a veritable thread of Ariadne. 



F. TiEDEMANN 



BIRDS in diverging from ancestral reptiles de- 

 veloped the hypopallium to the extreme 

 without corresponding elaboration of the 

 cortex; in fact, the cortex of birds appears to be 

 actually regressive as compared with any existing 

 reptiles. In mammals, on the other hand, the cortex 

 undergoes extensive differentiation and the lowest 

 living mammals have far more extensive and complex 

 cortex than any reptiles, while the corpus striatum 

 remains relatively small as compared with reptiles 

 and birds. The striatum complex also assumes a 

 form different from that of any reptiles, and as the 

 mammalian series is ascended it becomes progressive- 

 ly more completely detached from surrounding struc- 

 tures. The striatum complex of lower mammals con- 

 sists of the following parts (Fig. 27) : 



I. Laterally and posteriorly in the temporal lobe 

 there are the amygdaloid nuclei which receive part 

 of the great lateral olfactory tract and ascending fibers 



