MYCETES SENICULUS 213 



designation of a fifth hand, as in Ateles, none the less has become an organ 

 possessed of delicate sensory discrimination. It is probable that the acquisition 

 of such a prehensile tail is chiefly accountable for expansion in the column 

 of GoII since no further provocative specialization has occurred m the hind 

 leg or foot. 



One particular development in connection with the nucleus of Goli 

 is the median unpaired nucleus of Bischoff which is situated at the 

 caudal extremity of the dorsal sensory nuclei in juxtaposition to the dorsal 

 median septum. This nucleus was first described by Bischoff in 1899. It 

 develops according to Zeehandelaar in animals possessed of tails used pre- 

 hensilely, as in the spider monkeys, or as supporting organs in the kangaroos, 

 or as in the Cetacea acting as propelling organs. Its presence in mycetes 

 indicates the high degree of development of the prehensile tail in this 

 animal. 



Even more striknig, however, is the expansion of the column of Burdach 

 (CB) at this level, for which but one mterpretation seems reasonable, 

 namely, the appearance of a highly diff'erentiated hand. The degree of dis- 

 criminative sensibility now vested in the cutaneous and subcutaneous struc- 

 tures of this hand provides the ability to estimate the consistency of objects, 

 to detect differences in their size and shape, texture and temperature, mois- 

 ture and dryness, as well as other physical qualities which may be appreci- 

 ated by manual contact. To these sensory discriminations are added others 

 equally important because they take their significance from the sensory 

 impressions created by ne\\' ranges of motion. These new possibilities suggest 

 that there has evolved from the simple and but little differentiated forelimb 

 originally specialized for locomoticjn, an organ so highly modified that it may 

 almost be considered new. New also are the avenues of contact with life 

 which the hand has created, adding immeasurably to the stream of behavioral 

 reactions of which the animal is capable. 



