40 ON THE ORIGIN AND DEVELOPMENT OF THE 



cavity of reserve now begins to lengthen, to bulge out, and to 

 curve backwards and upwards at its posterior extremity, under 

 the form of a sac, into the mass of the maxillary tuberosity ; 

 a papilla or pulp appears in its fundus, and a process of con- 

 traction separates it from the remainder of the cavity of 

 reserve, which still adheres to its proximal wall by one 

 extremity, while by the other it is continued into the 

 substance of the gum under the anterior molar. Tliis new 

 sac, which is that of the second permanent molar, now 

 occupies the position in the maxillary tuberosity which 

 the first permanent did before it. It afterwards leaves this 

 retired position, in consequence of the lengthening of the 

 jaw allowing it to fall downwards and forwards into the 

 line, and on a level with the other teeth.* Before it leaves 

 the tuberosity altogether, the posterior extremity of the 

 remainder of the cavity of reserve sends backwards and 

 upwards its last offset — the sac and pulp of the wisdom- 

 tooth, which speedily occupies the tuberosity after the 

 second molar has left it, and ultimately, when the jaw again 

 lengthens for the last time, at the age of nineteen or twenty, 

 takes its place at the posterior extremity of the range of the 

 adult teeth. 



The wisdom-teeth are the second products of the posterior 



* The curved lines whicli the posterior cavities of reserve, and the sacs of 

 the molar teeth, describe in their progress to and from the maxillary tuber- 

 osity, and the coronoid process, and the peculiar position in which the pulps 

 are consequently developed, explain satisfactorily certain normal and abnormal 

 conditions of these teeth : — 1. The cm-ves wliich the combined giinding sur- 

 faces of the molar teeth present, convex downwards and backwards in the 

 upper jaw, concave upwards and forwards in the lower. 2. The peculiar 

 manner in which the fangs of the molars, partieidarly the inferior, are bent 

 backwards. 3. The occasional horizontal position of the wisdom-teeth, the 

 crowns of the inferior beiiig-du'ected forwards, those of the superior backwards. 

 This abnormal position is the cause of much annoyance and danger to the 

 patient, and of difficulty to the surgeon. 



