12 PROCEEDINGS OF THE ACADEMY OF [1893. 



regions answer roughly to those occupied by various kinds of teeth, 

 and differ in much the same way as the incisiform, caniniform 

 and molariform teeth differ from one another. The region of the 

 incisor teeth is compressed and beaked, that of the canine tooth and 

 the first bicuspid tooth is coarsely conical or tubercular, while that 

 of the second bicuspid and molar teeth is either broad and massive, 

 or compressed. It is rare to find an edentulous dental arch uni- 

 formly hyperostosed or uniformly atrophied, but one or more of the 

 regions above named assume the form described, or at least exhibit 

 indications of changes different in character from the mere loss of 

 the alveolar processes. 



The lower jaw passes up in front of the upper jaw in aged individ- 

 uals who have lost teeth. As a result, the attrition of the incisorial 

 region of the lower jaw is secured against the front of the upper jaw. 

 The result attained by such attrition Dr. Allen called " shearing." 

 Shearing takes place in proportion as the upper jaw at its anterior 

 arc is beaked. It is interesting to find that when "shearing" is 

 present the articular surface of the condyloid process is invariably 

 at the anterior part. 



The loss of the alveolar process in the incisorial region of the 

 upper jaw causes the incisive foramen to assume an absolutely new 

 position in relation to the line of mastication. It exhibits a dispo- 

 sition to lie in the dental arch instead of back of it. The attri- 

 tion by "shearing" however, protects the contents of the foramen 

 from pressure. 



The region in the upper alveolar arch directly back of the last 

 molar is apt to become symmetrically hyperostosed. These masses 

 appear to be dominated by the pyramidal process of the palatal 

 bones and the pterygoid process of the sphenoid bone. At least 

 they are not used for mastication. 



The subdivision of the teeth into kinds, which answer to the 

 incisors, canines, bicuspids and molars, correlates to the strongest 

 suture lines in the face, that is to say, the incisors correspond to the 

 premaxillo-vomerine junction, the canine and first bicuspid to the 

 fronto-maxillary junction, and the remaining teeth to the fronto-malar 

 junction. 



The edentulous skulls examined were 14 in number, distributed 

 as follows; Ancient Egyptian, 3; Arabian, 2; Hindu, 2; Peru- 

 vian, 2 ; Negro, 1 ; N. A. Indian, 2 ; Anglo-American, 2. Of this 

 number the Anglo-Americans alone could by any possibility repre- 

 sent the teeth of persons who could have worn artifical teeth, and in 

 this way modify the act of mastication in the aged. Since one of 

 the Anglo-American crania was that of an idiot, the probability is 

 reduced to a minimum that an artificial denture had been used 

 during life in any of the specimens examined. 



