272 THE LOWER PRIMATES 



thesis to any such skilled or learned performance has its origin in many areas 

 of the cerebral cortex is the generally accepted opinion of the present day. 

 According to this view each specialized area of the neopallium may, and 

 probably does, participate in the formulation of this incentive synthesis. 

 Kinesthetic sense, general body sense, vision, hearing, the sense of smell and 

 even of taste, together with certain higher discriminative faculties imparting 

 the elements of judgment, all contribute to this composite body of impulses 

 which finally combine to form an incentive synthesis. The genesis of the second 

 of the two concurrent streams is of equal importance. Each major functional 

 region of the cerebral cortex — such, for example, as the frontal, the parietal, 

 the temporal and the occipital lobe — gives rise to a group of fibers which, 

 becoming collected, enter the corona radiata, thence pass through the 

 internal capsule, into the cerebral peduncle, and ultimately end in the pons 

 Varolii. These are known as the pallio-pontile fibers. Their several subdivi- 

 sions are specifically indicated as the fronto-pontile, parieto-pontile, tcm- 

 poro-pontile and occipito-pontile contingents. Each contingent by means of 

 synapses in a large nuclear mass of the pons VaroUi, the pontile nuclei, gains 

 ultimate connection with the lateral lobes of the cerebellum. 



Those animals with small-sized lobes of cerebral cortex contribute 

 correspondingly small contingents to this pallio-ponto-cerebellar system. In 

 consequence, not only the number of fibers entering into the pons from this 

 source, but the size of the pontile nucleus necessary to relay them therein, is 

 correspondingly small. Hence, the animal equipped with a small cerebral 

 cortex must of necessity have a small pons Varolii. From the functional 

 standpoint, the smallness of the pons is indicativeof an animal poorly equipped 

 in the more complex varieties of skilled learned performances. For these 

 reasons the size of the pontile nuclei may also be employed as a reliable index 

 in estimating the degree of expansion in the cerebral cortex, and, from such 

 estimation, in arriving at an opinion as to the degree to which that animal 



