November, 1913. 



KNOWLEDGE. 



419 



its generalised character, but is beginning to show 

 depressions as the genial pit makes its appearance ; 

 then one has apes like the baboons, macaques, or 

 colobus monkeys with an exceedingly deep pit or 

 depression. Next come anthropoids, in which the 

 lower edge of the jaw is already being dropped into 

 something resembling a chin, and the depression at 

 once becomes less apparent. Next are some 

 jawbones of prehistoric man, namely, the Heidelberg 

 and the Naulette jaws, in which the depression is 

 still plainly seen and is scarcely less marked than in 

 the gibbon. 



It will be seen that the Heidelberg jaw shows on 

 its surface a tubercle ; indeed, I understand that one 

 of the descriptions of it published soon after it was 

 found stated that it did not differ from modern jaws 

 in this respect (see Figure 464). A brief comparison 

 with the other casts, however, will make it plain 

 that the tubercle here seen is too low down to be 

 that for the genio-glossus, and is plainly the one for 

 the genio-hyoid muscle mentioned in the earlier part 

 of this article, which has nothing whatever to do 

 with the tongue. This tubercle is quite common 

 among the apes. 



When we come to the Pygmies and Bushmen we 

 find in the majority of jaws the remains of this pit 

 or a mere flat surface ; but in some African dwarf 

 races, and among the Hottentots, Veddahs, and 

 Andamanese, two little prominences are seen 

 beginning to grow at the lower edge of the pit (see 

 Figures 442 to 452). These tubercles, as we pass to 

 higher and more civilised races, become more and 

 more prominent, until we get the European type 

 familiar to all students of anatomy. 



Now the bearing of these changes on the 

 functions of the genio-glossus muscle is fairly 

 evident. First of all, it needed a deep pit in the 

 lower apes to get room to work at all. Then the 

 depth of the pit became unnecessary through the 

 tilting of the lower surface of the mandible ; and by 

 means of this change the muscle was obviously given 

 greater freedom for action. Then we get a nearly 

 flat surface ; and finally a prominence appears, 

 enabling the separate fasciculi of the muscle to 

 spread from the very point of origin and so act 

 independently without hampering their neighbours 

 (see Figures 441, 455, 461, and 465). 



We are thus able to follow the whole course of 

 the history of the genio-glossus muscle from fossil 

 lemurs to modern men, and a very remarkable 

 history it is, difficult, I believe, to parallel in any 

 other structure of the body which we may pick out 

 for the purpose. We found it in the lower apes, in 

 which it first appears as an important factor in 

 tongue movements, coming out of a hole in the 

 lower jaw, and we take leave of it mounted upon a 

 pinnacle quite as high as the pit was deep (see 

 Figures 486 and 487). This is as if an organism 

 commenced its career in the uttermost depths of the 

 sea, and attained its full development at the top of 

 Mount Everest ! The muscle might stand above all 

 things else in our bodies as a symbol and sign of our 



upward progress. For I think it cannot be denied 

 that its development marched pari passu with the 

 development of intellectual capacities and the 

 increasing need of a means of clear expression. 



When speech began, as distinct from mere animal 

 stereotyped cries and other noises, it is, of course, 

 impossible to say. For the speech of certain low 

 savages, consisting of grunts, guttural sounds, and 

 clicks, it is fairly obvious that few tongue move- 

 ments are necessary ; but wherever languages have 

 become more elaborate — and many of them in 

 different parts of the world appear to have had an 

 independent origin from more brute-like utterances 

 — we find that the genio-glossus muscle comes more 

 and more into play, as is evidenced by its tubercles 

 of attachment and by the forward tilt of the chin to 

 give elbow room among all the higher races. 



The speech of monkeys is, of course, a myth, and 

 most of our anthropoid friends are curiously silent 

 beings. The two exceptions appear to be the chim- 

 panzee, which is described by travellers as shouting 

 and calling in varied tones in the forest, and certain 

 gibbons, which appear to come nearer to us in the 

 variety of articulate utterances than any other of 

 the Primates. From the series of plaster casts 

 shown in the plates, and in many others that are in 

 my possession, it seems to become evident that, 

 speaking generally, the genial tubercles may be taken 

 as some index of social and intellectual development. 

 They are not, of course, strictly necessary for speech, 

 but it is clear, both from anatomical and general 

 reasons, that they greatly facilitate speech. 



It is interesting to watch their development in the 

 normal human subject (see Figures 453 to 455), and 

 I have several casts which illustrate this fairly 

 clearly. In all young children they are absent, and 

 up to the age of fourteen years they make but a 

 small show ; in fact, the jaw of a child of fourteen 

 years almost exactly resembles in this respect that of 

 a Bushman or Pygmy ; between fourteen and seven- 

 teen, however, they appear to obtain their full 

 development. How far that development is 

 dependent upon the use of the muscle it is difficult 

 to say ; my own belief is that, like many of the 

 roughnesses and ridges upon our bones, they are 

 very largely the product of vigorous muscular 

 action, i.e., Nature has met the obvious need of the 

 muscle by altering the bone in a certain specific 

 direction. 



For many years I have been endeavouring to get 

 evidence as to the presence or absence of the 

 tubercles in deaf mutes. Such as I have, so far as it 

 goes, seems to show that in adults who have never 

 acquired articulate speech they are quite absent 

 (see Figure 440). In the one specimen I have 

 from a deaf mute, the bone almost exactly resembles 

 that of a Bushman, or a child of fourteen. 



A glance over the peculiarities of the tubercles in 

 the accompanying plates shows how extraordinarily 

 variable they are in different individuals and in 

 different races (see Figures 457 and 458), but before 

 any safe generalised conclusions are drawn 



