26 



ON THE ORIGIN AND DEVELOPMENT OF THE 



new sac and pulp of a smaller size (7) had appeared buried in 



the base of that process. The cavity 

 (b) was again lengthened out, being 

 attached anteriorly, at the anterior 

 edge of the base of the process, to 

 the gum, and posteriorly to the top 

 of the new sac (7). That portion of 

 the cavity formerly attached to the 



sac (6) was now almost obliterated. 



15. The posterior part of the .lower jaw of a child about 

 six years old was prepared by removing a section from its 

 internal posterior aspect, and making at the same time a 

 longitudinal section of the gum. 

 The sac (7, Fig. 26) had ad- 

 vanced from under the coronoid 

 process ; and another very small 

 sac and pulp had appeared en- 

 closed in a bony crypt under 

 the process, and communicat- 

 ing through the upper part of the bony cell of the sac (7) 

 with the gum, where it terminated in an opaque line or tail, 

 the last remains of the surface of adhesion of the dental groove. 



SECTION II. A DESCRIPTION OF THE PULPS AND SACS FROM 

 THEIR FIRST APPEARANCE IN THE EMBRYO TILL THE 

 ERUPTION OF THE WISDOM-TEETH. 



When we examine the upper jaw of a human embryo at 

 the sixth week, there is perceived between the lip and a semi- 

 circular lobe of a horse-shoe form (which is the primitive 

 condition of the palate) a deep narrow groove which ter- 

 minates on each side, behind the former, by curving inwards 

 on the soft mucous membrane. As this groove becomes 



