THE INTEGUMENT AND THE EXOSKELETON 93 



species. The thenar pattern has here become entirely re- 

 duced, but is often present. The apical patterns are also 

 modified, but in a lateral view would show the triradii. 



Inasmuch, however, as in the Primate hand and foot the 

 ridges are still of considerable functional importance, they 

 are apt to become modified at each point of the surface in ac- 

 cordance with the use of that point, and it thus happens that 

 in different species and in different parts of the surface there 

 are varying degrees of faithfulness to the ancient records. 

 Thus in Macacus the use of the hand is such that thenar, 

 hypotheriar and apical pads tend to degenerate, while the in- 

 terdigitals are preserved in their typical relations, while in the 

 human hand the reverse is the case, and the apical patterns are 

 nearly always well marked, and often in the form of typical 

 whorls with two lateral triradii ; while the interdigital patterns 

 are usually lost or obscurely indicated. A hypothenar pattern 

 is frequent, especially in the white race, and occasionally oc- 

 curs as a whorl with three triradii ; but the thenar is of rare 

 occurrence, and then usually associated with the first interdigi- 

 tal. These changes are in part explained by the tendency of 

 the ridges to assume an approximately transverse direction, 

 a tendency in which the right hand has surpassed the left, 

 owing to the long preferential use of the former. 



In the human foot the apical patterns are about as well 

 marked as in the hand, but with a smaller percentage of the 

 primitive whorl type ; the four interdigital pads are fairly well 

 indicated and often appear in infants as rounded elevations. 

 Of .these the most constant is .the first, placed on the balPof 

 the foot below the great toe, and is frequently of the whorl 

 type, occasionally with three triradii; the primitive condition 

 again corresponding to the functional importance of the region 

 which here bears the main force of the body during a portion 

 of each step. The hypothenar is occasionally indicated by 

 a loop on the outer edge, but the thenar is practically lost. 

 An additional loop, of uncertain morphological significance, 

 occasionally occurs on the heel. 



