STORY OF THE CHIN——ROBINSON. 603 
of attachment for a little muscle which appears to be equally devel- 
oped in man and in many of the lower creatures. It is known as the 
genio-hyoideus and has no connection with the tongue. 
A close examination of the larger bony prominences, or the genial 
tubercles proper, reveals some very interesting and remarkable facts, 
especially when we employ comparative methods. To these are 
attached the tendon of the fanlike genio-glossus muscle which spreads, 
out beneath the whole lower surface of the central region of the 
tongue and penetrates through the intrinsic muscles almost to the 
upper surface. (See figs. 64, 65.) Now if we examine any of the 
current books on anatomy, little or no suggestion is found that the 
functions of the genio-glossus muscle have to do with articulate 
speech. Let us leave the mandible for a while and confine our atten- 
tion to the structure and functions of this muscle, and I think it will 
soon become’ evident that it has more to do with the oral (as distinet 
from the laryngeal) machinery of articulate speech than any other 
structure. 
In the diagrams (see figs. 66-71), which show the under surface of 
the tongue of man and other creatures more or less related to him, it 
is seen how remarkably this muscle has become developed since we 
became human. The functions accorded to it in our standard works 
of anatomy would apply to the needs of the dog and the pig equally 
to those of man; yet we see that in these animals it is a mere feeble 
slip of flesh which can exercise but little influence. 
I have dissected it in a good many apes, among which animals it 
evidently had somewhat important duties quite apart from vocal pro- 
duction; in fact, | doubt whether in any other creature except in man 
we should find the tongue interfermg in any way whatever in the 
sounds which issue from the larynx: The muscle is not only much 
smaller in apes than in man, but it is much more homogeneous and 
compact (see fig. 63); while, so far as I have been able to observe, 
the method of innervation shows an even greater difference than is 
seen in the structure of the muscle itself. To put the matter very 
briefly, im man the genio-glossus has become a series of a large num- 
ber of independent muscular strips which are, to all intents and pur- 
poses, separate muscles, each with its little fiber of the hypoglossal 
nerve entering it in such a way as not to hamper its free movement, 
while in the apes it is apparently a single muscle, or a closely united 
group, acting en bloc. 
It must be remembered that the adoption of an exceedingly im- 
portant new method of expression and communication such as human 
articulate speech would require widespread and most elaborate 
changes in the structures which it brought into play. It is not 
possible on the present occasion to go into the marvelously intricate 
cerebral, nervous, and muscular machinery, with its innumerable 
