14 PROCEEDINGS OF THE ACADEMY OF [1893. 



display the uniformity seen in the four exhibited. In the future, 

 the greatest variations will certainly be exhibited. In some a prom- 

 inence will be present, which in life amounted to almost a monstros- 

 ity, while in others there will be found a complete atrophy or 

 absorption of the entire ridge in both the superior and inferior 

 maxilla. The symmetry of the ridge will in a measure be due to 

 the uniformity of pressure from an artificial denture, and an absence of 

 the forces alluded to by Dr. Allen, which doubtless had had in some 

 cases an influence in the secondary development of bony structure, 

 while those parts were forced to perform the function of the teeth 

 which had been prematurely lost, though some of the prominences 

 to which attention had been drawn, were, in the estimation of Dr. 

 Pierce, due to the difference in the time of the loss of the teeth. 

 Why some maxillaries should show such complete atrophy, while 

 others had secondary development, Dr. Pierce could not explain, but 

 he believed it was associated with temperamental and nutritional 

 conditions. The development certainly indicated a healthy recupera- 

 tive power on the part of the individual. 



With reference to the protrusion of the lower jaw and chin, and the 

 change in adaptation of condyle to glenoid cavity, which Dr. Allen 

 had so aptly illustrated, Dr. Pierce thought they could be explained 

 upon the principle of use and disuse, with adaptation of structures. 

 In infancy, the angle resulting from the relation of the ramus to the 

 body of the bone was much greater than a right angle, indeed the 

 ramus was but little above the same horizontal plane occupied by the 

 body of the bone, and the jaw was capable only of vertical and antero- 

 posterior motion, such as is essential to sucking or nursing. As the 

 three true or permanent molars are developed, the ramus assumes its 

 vertical position, forming almost a right angle with the body of the 

 bone, and at the same time making lateral or horizontal movement 

 possible while establishing the concomitant relation between the 

 condyles and glenoid cavities. As these permanent molars later in 

 life are lost, the force upon the jaw in occlusion is confined to the 

 anterior part or incisive locality, which would necessarily tend to 

 increase the angle and protrude the chin. This occurs sometimes 

 quite early in life and while all the anterior teeth are in position. 

 At the same time that the vertical motion is exerting this influence 

 the necessity for lateral motion has ceased, by the loss of the 

 grinders; hence the change in the relative position of the condyle, 

 which was so well shown by the previous speaker, and which has 

 been necessitated by a return to the vertical and anteroposterior 

 motion common to infancy, with the loss of the horizontal or lateral 

 motion of maturity. 



In consequence of his election to the office of Treasurer, Mr. 

 Chas. P. Perot resigned from the Finance Committee. Dr. Geo. H. 

 Horn was elected to fill the vacancy. 



