238 



THE AMEBIC AX XATERA LIST 



[Vol. L 



less. The absence of this bony projection in the face is 

 in fact one characteristic thing in our more or less ape- 

 like forefathers (Figs. 3 and 4). The question is, how 

 the " evolution ' 1 of this chin is to be explained. 



Dr. Eobinson's explanation seems to me to boil down 

 to this: that man is, before all other creatures, a talker. 

 In talking, the genio-glossus muscle is called upon to do 

 the most work. This is a fan-shaped muscle which com- 

 poses a large part of the under portion of the tongue, and 

 is attached to the inner surface of the jaw just within 



the chin. It is, according to Robinson, larger, more 

 specialized in structure and more fully fasciculate in man 

 than in the monkeys. The chin, then, says Eobinson, is 

 the point of origin for this elaborate muscle, which in a 

 minute of conversation makes several hundred separate 

 movements. The chin has crowded forward in its pres- 

 ent conspicuous form as successive generations of men 

 developed more adequate apparatus for speech. In other 

 words, the chin developed because of the use and the 

 consequent development of this one " talking-muscle. ' ' 



It is only fair to remark that this is an old discussion. 

 Walkhoff, in a series of papers, beginning with a volume 

 edited by Selenka in 1901, 1 put forward the theory now 

 rejuvenated by Robinson. The suggestion was critically 

 reviewed by Fischer in a series of articles. 2 Since then 

 the idea has appeared in a variety of journals. 



i Ausz. Biol. Cent ralbl., Volume 22. 



Especially Anat. Am., Volume 23 (1903); Volume 25 (1904). 



