314 THE POPULAR SCIENCE MONTHLY. 



commoner, rising to seven per cent. In modern civilized races 

 the percentage ranges from five to ten. In following out the de- 

 tails of this enumeration I have spoken as if the microdontal con- 

 dition had been the primary one, whereas all the available evidence 

 leads to show that the contrary was the case. The characters of 

 all the early crania, Neanderthal, Engis, and Cromagnon, are those 

 of macrodonts. The progress has been from the macrodont to 

 the microdont, as it probably was from the microcephalic to the 

 macrocephalic. 



The effects of the variations in size of the teeth are numer- 

 ous and far-reaching. The fluctuation in the weight of the jaw 

 depending on these variations has an important influence on 

 the center of gravity of the head, and affects the set of the 

 skull on the vertebral column. This leads to a consequent 

 change in the axes of the occipital condyles, and it is one of 

 the factors which determine the size of the neck-muscles, and 

 therefore the degree of prominence of the nuchal crests and mas- 

 toid process. 



As the teeth and alveolar arches constitute a part of the appa- 

 ratus for articulate speech, so these varieties in dental develop- 

 ment are not without considerable influence on the nature of the 

 sound produced. The necessarily larger alveolar arch of the 

 macrodont is hypseloid or elliptical, more especially when it has 

 to be supported on a narrow frontal region, and this is associated 

 with a more extensive and flatter palatine surface. This, in turn, 

 alters the shape of the mouth cavity, and is associated with a wide 

 flat tongue, whose shape participates in the change of form of the 

 cavity of which it is the floor. The musculature of the tongue 

 varies with its shape, and its motions, upon which articular speech 

 depends, become correspondingly modified. For example, the 

 production of the sharp sibilant S requires the approximation of 

 the raised flexible edge of the tongue to the inner margins of the 

 teeth behind the canines, and to the palatine margin close behind 

 the roots of the canine and lateral incisor teeth. This closes the 

 vocal tube laterally, and leaves a small lacuna about 5 mm. wide 

 anteriorly, through which the vibrating current of air is forced. 

 A narrow strip of the palate behind the medial halves of the 

 median incisors bounds this lacuna above, and the slightly con- 

 cave raised tongue-tip limits it below. 



With the macrodont alveolar arch, and the correspondingly 

 modified tongue, sibilation is a difficult feat to accomplish, and 

 hence the sibilant sounds are practically unknown in all the Aus- 

 tralian dialects. 



It is worthy of note that the five sets of muscular fibers, whose 

 function it is to close laterally the flask-like air-space between 

 the tongue and the palate, are much less distinct and smaller in 



