THE TEETH. 61 



These " reserve sacs" at first lie above the milk sacs, but by 

 degrees they retreat backwards, and are received into hollows 

 of the bony alveoli as they are formed round the milk teeth 

 (fig. 195, g, h.) Those of the incisors and canines eventually 

 become completely separated from the alveoli of the cor- 

 responding milk teeth, but those of the premolars 1 open into 

 the bottom of the alveoli of the deciduous molars. 



The sacs of all these teeth are produced at their apices into 

 a solid cord, which extends either to the gum, or, as in the two 

 premolars, to the periosteum in the bottom of the alveoli of 

 the two deciduous molars (fig. 195, i.) } and has been erroneously 

 described as a gubernaculum, or guiding cord for the teeth in 

 their eruption. 



The sac of the anterior of the three permanent molars, arises, 

 together with its papilla, in the sixteenth or seventeeth week, 

 quite independently, from the posterior extremity of the primi- 

 tive dental groove, and closes in such a manner that a reserve 

 sac remains between it and the mucous membrane (Mikr. Anat. 

 fig. 206). It is not till the seventh or eighth month after 

 birth that the latter elongates behind the first sac, arches into 

 the margin of the jaw, produces a papilla from its base, and 

 becomes constricted off into the sac of the second molar. The 

 remainder of the cavity falls into a line with the other sacs, 

 and forms that of the wisdom tooth. 



The formation of milk teeth begins at about the fifth month 



1 [Instead of the loose phraseology " small" and " large" molars, &c., we have 

 adopted the philosophical nomenclature of the teeth, introduced by Professor Owen, 

 (see his Article on the Teeth, in Todd's Cyclopaedia) and thus explained by him : 

 " Those teeth which are implanted in the premaxillary bones, and in the correspond- 

 ing part of the lower jaw, are called "incisors," whatever be their shape or size ; the 

 tooth in the maxillary bone, which is situated at or near to the suture with the pre- 

 maxillary, is the "canine," as is also that tooth in the lower jaw, which in opposing 

 it, passes in front of its crown when the mouth is closed. The other teeth of the first 

 set, are the " deciduous molars;" the teeth which displace them vertically, are the 

 " premolars :" the more posterior teeth which are not displaced by vertical successors, 

 are the molars properly so called." 



It results from this, that the so-called bicuspid and "first molar" of the permanent 

 set in man (Professor Kblliker's " small molars") are the premolars ; being, in fact, 

 the third and fourth of the typical dentition ; the first and second premolars and the 

 third incisor of the typical dentition, not being developed in man. The nomencla- 

 ture of the teeth, from being merely technical and arbitrary, has thus, by Professor 

 Owen's recourse to development, become scientific. — Eds.] 



