OUR FACE FROM FISH TO MAN 



the geniohyoglossus muscles have acquired the abil- 

 ity to change the precise shape and position of the 

 different parts of the tongue with extreme rapidity 

 and in conjunction with movements of other parts 

 of the voice-producing mechanism (Robinson). 



The great size of the tongue in man and its 

 important function as the leading organ of speech 

 has doubtless partly conditioned the later stages 

 in the evolution of the lower jaw, especially in the 

 region of the chin, to the back of which the tongue 

 muscles are attached (Fig. 68). 



Meanwhile the remaining part of the branchial 

 arches has given rise to the larynx with its highly 

 elaborate voice mechanism, to the tonsils, thyroid 

 and thymus glands, the last two being of vital 

 importance in the normal growth and differentia- 

 tion of the individual. Again the anti-evolutionist 

 can offer no alternative scientific explanation of 

 the fact that during the course of embryonic 

 development the human tongue, larynx and 

 adjacent structures reveal remarkably detailed 

 resemblances to corresponding structures of lower 

 vertebrates.' The "gill-slits" in the human 



' For a clear presentation of the details see Keith, Arthur, 1921, 

 Human Embryology and Morphology, London, pp. 240-252. 



126 



