November, 1913. 



KNOWLEDGE. 



417 



are to be found in practically all European and in 

 most other jawbones two bony prominences known 

 as the genial tubercles (see Figure 441). Below 

 them are two somewhat similar prominences, 

 generally much smaller (which often appear as 

 faint convergent ridges), which are also known to 

 anatomists as genial tubercles; but these, I think, 

 we need not consider of any importance in the 

 present argument. They are to be found, not only 

 in the lowest savages and in prehistoric men, but also 

 in a large number of the apes and other vertebrates ; 

 indeed, I have detected apparent traces of them 

 in those strange Permian reptiles of incalculable 

 antiquity to which allusion was made above. They 

 are the points of attachment for a little muscle 

 which appears to be equally developed 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 Figures 487 and 488). 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 attention 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 dis- 

 tinct from the laryngeal) machinery of articulate 

 speech than any other structure. 



In the diagrams (see Figures 489 to 494), 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 production ; in fact, I 

 doubt whether in any other creature except in man 

 we should find the tongue interfering 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 Figure 486) ; 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, in 

 man the genio-glossus has become a series of a large 

 number of independent muscular strips which are, to 

 all intents and purposes, separate muscles, each with 



its little fibre 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 important 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 marvellously intricate cerebral, nervous, and 

 muscular machinery, with its innumerable bonds of 

 coordination required for ordinary speech ; but a 

 little search into the matter will show anyone that 

 we are here in contact with one of the most incre- 

 dible marvels in Nature. Most wonderful of all, the 

 whole mechanism is, from an evolutionary standpoint, 

 quite new — a product of merely the later fragment 

 of a brief geological period ! 



When we consider the number of movements, 

 following one another in continually varying order, 

 required for articulate speech, it is obvious that only 

 machinery which is able to act with every 

 mechanical advantage and with a minimum of 

 friction, can accomplish such a task with precision. 

 Public speakers frequently talk at the rate of one 

 hundred and fifty words a minute, while it seems 

 possible to articulate quite clearly and correctly 

 when speaking at the rate of one hundred and eighty 

 words a minute. If we analyse the action of the 

 tongue when speaking at the rate of one hundred 

 and fifty words a minute, we find that there must be 

 at least five hundred different movements or adjust- 

 ments. This gives eight or nine in every second ! 

 Such movements, it must be remembered, do not 

 follow one another regularly in mechanical rotation 

 like the piston-beats of a multiple-cylindered engine, 

 but are continually varying their order. What 

 wonder is it that coordination sometimes breaks 

 down, with the result of a stutter or a stammer ? 



Now a brief examination of the intrinsic muscles 

 of the tongue, i.e., those that begin and end in the 

 tongue itself like the distal muscles of an elephant's 

 trunk, will show how totally inadequate these would 

 be to produce any such result ; but immediately one 

 takes careful note of the mode of action of the genio- 

 glossus muscle the solution of the tongue's incredible 

 agility becomes possible. 



It is seen in the accompanying diagrams (see 

 Figures 495 to 499) that the several bundles, or 

 fasciculi, of the muscle are able to act more or 

 less at right angles to the main plane of the tongue 

 without anything to hamper them. For each flash- 

 like movement of the tongue away from the palate 

 all that is demanded is an instantaneous shortening 

 of one or other of these independent strips. For 

 instance, in pronouncing the letter T we place the 

 tip of the tongue against the palate close to the 

 upper incisor teeth (see Figure 498), and then 

 snatch it away with great rapidity. The placing 

 it there is probably the work of the intrinsic muscle 

 called the superior longitudinal lingual, but the 



