PULPS AND SA.CS OF THE HUMAN TEETH. 39 



of communication is never removed from the sockets of the 

 latter. 



The cords of communication which pass through these 

 foramina are not tubular, although in some instances a portion 

 of the unobliterated extrafollicular compartment of the ori- 

 ginal little cavity of reserve may be detected in them. They 

 are merely those portions of the gum which originally contained 

 the lines of adhesion of the depressions for the permanent 

 teeth in the secondary dental groove, and which have been 

 subsequently lengthened out, in consequence of the necessarily 

 retired position in which the permanent teeth have been 

 developed during the active service of the temporary set. 

 The cords and foramina are not obliterated in the child, 

 either because the former are to become useful as " guber- 

 nacula," and the latter as " itinera dentium," or much more 

 probably, in virtue of a law, which appears to be a general 

 one in the development of animal bodies viz. that parts 

 or organs which have once acted an important part, however 

 atrophied they may afterwards "become, yet never altogether 

 disappear so long as they do not interfere with other parts or 

 functions. t 



The sacs of the permanent teeth derive their first vessels 

 from the gums ; ultimately they receive their proper dental 

 vessels from the milk-sacs, and as they separate from the 

 latter into their own cells, the newly-acquired vessels con- 

 joining into common trunks, retire also into permanent dental 

 canals. 



It was stated above that, in the child at the seventh or 

 eighth month, when the central incisives were passing through 

 the gums, the jaw had lengthened so much as to allow the 

 first permanent molar to retire from the maxillary tuberosity, 

 and to resume in some measure its position downwards and 

 forwards in the same line with the other teeth, and also to 

 reduce the great cavity of reserve to its primitive size. This 



