PULPS AND SACS OF THE HUMAN TEETH. 27 



gradually wider, and the lip more lax in a direction from 

 behind forwards, there appears on its floor posteriorly, and 

 proceeding in the same direction, a ridge (the external alveolar 

 process) which speedily divides the original groove into two 

 others ; the outer one forming the duplicature of mucous 

 membrane from the inside of the lip to the outside of the 

 alveolar process, the inner one constituting what may be very 

 properly denominated the primitive dental groove, as the germs 

 of the teeth appear in it. 



The inner side of the ridge already mentioned, after being 

 cut into three grooves whose concavities look inwards, and of 

 which the posterior is the deepest, terminates in a rounded 

 lobule, which is continuous with it anteriorly, while externally, 

 internally, and posteriorly, it is bounded by that portion of the 

 original groove which was situated behind the semicircular 

 lobe. The curves of the ridge are occupied by bulgings of 

 the semicircular lobe, so that the ridge and lobe, with their 

 curves and bulgings, are exactly similar to the arrangement 

 of the mucous membrane of the second compartment of the 

 stomach of the porpoise. 



At some period between the sixth and seventh week a 

 longitudinal portion is cut off from the internal posterior edge 

 of the semicircular lobe, extending as far forwards as the 

 middle bulging, and about the same time the posterior bulging 

 becomes isolated and defined, under the appearance of an 

 ovoidal papilla, the long diameter of which is antero-posterior. 

 This papilla is the germ of the anterior superior milk-molar 

 tooth, the first tooth-germ which appears in the development 

 of the human body. It is at this period a simple free 

 granular papilla, like many others on the surface of the 

 mucous membrane and skin. 



About the eighth week or second month a second papilla 

 appears at the point of projection of the ridge, between the 

 middle and anterior curve. This papilla, which is the germ of 



