PULPS .tND SACS OF THE HUlkLVN TEETH. 35 



defined apices of the cavities, and are strictly analogous to the 

 opercula of the niilk-follicles. 



The distal WM gradually acquires the appearance of a 

 tooth-pulp, Avhile the proximal disappear by the obliteration 

 of the little undefined space beyond them. 



Tlie cavities of reserve have now become tooth-sacs, and 

 imder this form they continue to recede from the surface of 

 the gum, imbedding theiuselves in the submucous cellular 

 tissue, \vhich has all along constituted the external layer 

 of the milk-sacs, and in which the larger saccular vessels 

 ramify before arriving at the true mucous membranes of 

 the sacs. This implantation of the permanent in the 

 walls of the temporary tooth-sacs gives the former the 

 appearance of being produced by a GE^DIIPAROUS process 

 from the latter* 



The dental groove was originally imbedded in an alveolar 

 groove. As the dental interfollicular septa are developed in 

 the former, osseous septa also begin to be formed in the latter. 

 These osseous septa are at first in the form of bridges, but 

 ultimately, at the sixth month, become complete partitions. 



* It was this imbedding of the permanent in the walls of the temporary 

 tooth-sacs which deceived Dr. Blake, and led him to suppose that the former 

 derived their orirpii from the latter. Mr. Fox supported the same ^new of the 

 subject ; and Mr. Bell, in his own work {Anatomy, etc. etc. of the Teeth, p. 

 61), and more lately in his notes in Palmer's edition of Mr. Hunter's Works, 

 vol. iL p. 37, has strongly urged the .same doctrine. Mr. Bell has stated that 

 Mr. Hunter's '• account of the manner in which the permanent teeth are formed 

 is exceedingly imperfect," but it is evident tliat if the accoimt of the origin of 

 these teeth given in the text be correct, Mr. Hunter was not in error when he 

 supposed botli sets to be of independent origin. Mr. Hunter was so correct a 

 thinker, that he did not account the circumstance of contiguity to be a proof 

 of dependence. He wius apparently ignorant of the origin of both sets, and in 

 his usual cautious manner, wlu-n describiiuj structure makes no ol>scr\'ation on 

 the subject. Tlie autlior of the Edinburgh Dissector hohls tin* same opinion as 

 Mr. Hiuiter on tliis subject ; and in his excellent chajiter on the teeth, although 

 he does not disprove the opinions of Dr. Blake and others, cautions the student 

 against supposing Mr. Hunter to be incorrect on this subject. 



