CRANIA FROM THE MOUNDS OF FLORIDA. 435 



It is, perhaps, owing to the exceedingly wide range of these modifications that 

 anatomists have not availed themselves of characters thus afforded in the study of 

 the skull as an aid in the identification of race types. The muscles which are most 

 important are those that move the head on the vertebral column. The bones enter- 

 ing into the temporal, zygomatic and pterygoid fossae are modified by the muscles of 

 mastication. The shape of the angle of the lower jaw appears to be due to the 

 action of the masseter and internal pterygoid muscles, as is also the size of the 

 ascending ramus. 



VI. A Study of the Teeth. 



The manner in which teeth follow one another in a given series (here called 

 their alignment), the directions of their "wear" and displacement (the results of 

 mastication and age), are of interest. To a short account of these conditions a 

 plan of studying cusps is appended. The titles of sections will appear as follows : 

 (a) Alignment, "wear" and displacement of the teeth ; (b) The cuspidation of the 

 premolars and the molars together with a statement of the order of succession of 

 the cusps. 



(a). Alignment, " wear" and displacement of the teeth. ■ Two tendencies 

 of alignment are recognized in the teeth, — that of the molar and that of the incisor 

 line. The molar line is that to which the molars conform. When projected for- 

 ward the molar line always embraces the second premolar (which appears to be the 

 rule in mammalian dentition), but the first premolar and the canine are often not 

 in the molar line as projected, but in a line which answers to that of the incisors. 

 The incisor line in its simplest expression is confined to the incisors. If the enamel 

 is worn it is easy to align the transitional teeth, namely, the first premolar and the 

 canine, to the molar or incisor line respectively. The effect of these differences in 

 alignment upon the shape of the jaw has not been elaborated at this place, but 

 it cannot be ignored. 



By the torsion of teeth is meant the change in the inclination of the crown 

 axis either forward or backward of the one which is normal. Examples of torsion 

 are seen in the first and second upper molars, and in the lower premolars. In figure 

 30, for example, the square crown-faces of the first molar and the third molar, figure 

 33, yield a medio-lateral axis, which forms a right angle when intersected by the 

 line of the alveolar process. In figure 32 the oval crown face of the first molar 

 yields a medio-lateral axis which does not form a right angle with the line of the 

 alveolar ridge. 



The torsion of an upper molar may be expressed by the disposition of the pro- 

 cone to touch the metacone to form the oblique ridge which is characteristic of the 

 tooth. If exaggerated, the tooth forms an elongated ellipsoidal crown. Now the 

 normal form is always in a series whose anterior and posterior walls touch each 

 other, and the ellipsoidal is not apt to be in close contact with other teeth. 1 infer 



