254 THE LOWER PRIMATES 



participate in the intimate specializations occurring in the upper extremity. 

 It involves those widespread adaptations concurrent with and consequent 

 upon the hberation of the forehmb from the responsibilities of locomotion. 

 It enters into the complete assumption ol upright posture, and modilication 

 of the lower extremities essential to this purpose, together with acquisitions 

 of muscular coordination incident both to bipedal locomotion and the per- 

 fection of manual dexterity. 



Planimetric and Longitudinal Coefficients of Olixarv Body. Evi- 

 dence in support of this view is tound even in the lower primates where the 

 comparison of lemur, tarsier, marmoset and mycetes reveals a progressive ex- 

 pansion in the inferior olive. The accompanying tabulation of the planimetric 

 coefficients of the nucleus indicates a volumetric increment of lOO per cent or 

 more in the olive of mycetes as compared with the other three species. 



Longitudinal coefficients of the olivary body, however, show even more 

 extensive change. Together these two mensurations confirm the supposition 

 that the inferior olive almost entirely expresses its expansion transversely 

 within the limits of the oblongatal segments. It differs from the spinal pre- 

 cerebellar nuclei whose expansion is chielly longitudinal. From a functional 

 comparison of these four species it is clear that manual performances in 

 mycetes are more complex and have a greater range of adaptability. As a 

 structural indicator of this phyletic progress the inferior olive is of especial 

 significance. It denotes the proficiency attained in the simultaneous move- 

 ments of the eyes, head and hands. 



Coefficients of the Inferior Oli\ e in the Lower Primates 



