984 EXOLLTIONAL MODIFICATIONS 



impulses from the lower extremity and tail, it has an extensive sensory field 

 to ser^e in its capacity as relay station. The cuneus is concerned with the 

 influx from the upper extremity. In certain of the lower primates, more partic- 

 ularly in those which possess a highly developed prehensile tail, this disparity 

 between the clava and the cuneus is most pronounced. In such species, the 

 column of Goll is larger than that of Burdach. This augmentation is in fact 

 signalized by a special element, known as the nucleus of Bischoff. The Bischoff 

 nucleus makes its appearance only in those animals possessed of a prehensile 

 tail or one specialized for direct participation in locomotion. The subsequent 

 disappearance of this median unpaired nucleus, and the gradual loss of the 

 clava's preponderance over the cuneus, with the involution of the tail, is a 

 matter of much evolutional significance. The clava actually becomes less 

 prominent and smaller than the cuneus in the intermediate primates. The 

 disparity is more marked in the gibbon, which has no tail, and in which the 

 upright posture is but tentatively and occasionally assumed. The progressive 

 emphasis of appendicular specialization, imposed by the development of the 

 hand, completes the supremacy of the cuneus in the sensory field. This final 

 predominance of sensory areas for the hand has a more far-reaching effect 

 than its influence upon the sensory sphere alone. The richness of all motor 

 specialization rests necessarily upon a substratum of sensory apperception, 

 in order that the kinesthetic associations, built up in connection with each 

 newly acquired motor performance, may be adequate to direct its execution 

 and to reconstruct its formula for future repetitions. 



Evolutional Significance of the Development of the Special 

 Senses. If there is much to indicate the waning of olfactory sense, as various 

 anthropoid stages are traversed in approach to the ultimate conditions in the 

 human brain, so also there is evidence of a vast change in two other realms of 

 special sense. In the case of olfactory sensibility, the process is one of actual 

 involution. With sight and hearing the matter stands otherwise. Here the 



