106 CHARLES MIDLO AND HAROLD CUMMINS 



Papio, Lasiopyga, Hylobates, Pongo, Gorilla and Homo. The 

 most common form of blending of Th and I is shown in the 

 occurrence of a pattern centered in the area of I, with its 

 peripheral portion extended into the territory of Th (as in 

 figs. 239-242). Together with this there are cases in which 

 the pattern center is less definitely assignable to I, being situ- 

 ated far enough proximally to lie in a zone properly belonging 

 to both Th and I, or in which there is a single continuous 

 open field. Mergers of the two configurational fields may be 

 regarded as characteristic in the genera having the majority 

 of hands thus marked: Saimiri, Cebus, Papio, Lasiopyga, 

 Erythrocebus, Hylobates, Pongo, Gorilla, Pan, Homo. Num- 

 bers amounting to about half the hands with blending of Th 

 and I occur in Lemur, Pithecus and Pygathrix. Lesser fre- 

 quencies occur in Tarsius, Alouatta, Aotus, Ateles and 

 Lagothrix. 



Interdigitals II, III and IV are the most constant of all con- 

 figurational fields, in the consistency with which they may be 

 made out as separate areas. The constancy of expression 

 of individual configurational fields appears to be a mark of 

 primitiveness. Primitiveness of these interdigital regions is 

 further expressed in their general tendency to the formation 

 of conspicuous patterns. The main irregularities are noted 

 in Hylobatidae, where the open fields representing II, III 

 and IV are commonly fused in the absence of limits provided 

 by digital triradii. In Pan and Gorilla such fusions occur, 

 though less frequently. With the small number of gorilla 

 hands the relative frequency of this condition cannot be de- 

 termined reliably, but the suggestion is that departures of 

 this nature are less common than in Pan. The occurrence 

 of fusions of configurational areas, virtually limited to the 

 apes and man, is of importance in relation to the relatively 

 low degree of pad development. As another expression of 

 instability of the interdigital fields, noted especially in Gorilla 

 (figs. 564, 568) and Pan, and more marked in the former, are 

 slight but appreciable displacements of patterns from the 



