PULPS AND SACS OF THH HUMAN TK1.TH. 43 



canines, and bicuspid.s ; the two posterior for that of the second 

 and third molar,* the coronoid process acting the part which 

 the maxillary tuberosity did in tlie upper jaw. 



Sfxtion III. 



1. On the Division of Dentition into Sta/jcs. — As dentition 

 is a process, not only very complicated in its details, but of 

 very lengthened duration, extending over nearly eight months 

 of intra-uterine, and above twenty years of extra-uterine 

 existence, the understanding and further investigation of it 

 may be facilitated by dividing it into stages. The most 

 natui-al division, one which is not artiticial, but clearly indi- 

 cated by the phenomena themselves, is into three stages, 

 according to the position of the pulp in relation to its con- 

 taining cavity — 1-^t, follicular stage ; 2d, saccidar ; 'id, eruptive. 

 We ought probably to consider, as anterior to the follicular, 

 the papillary stageT during which the fi)llicle or sac does not 

 exist, and the future pulp is a simple papilla on the free surface 

 of the gastro-intestinal mucous membrane. As this stage, 



• The cavities of reserve are occasionally somewhat undefined, two or three 

 being conjoined, particularly irosteriorly. Sooner or later, however, they 

 become distinct. The great cavity t'reiiuently stretches forwards over the sacs 

 of the milk-molars. 



t Most anatomists have supposed the germs of the teeth to appear as shut 

 sacs, full of a fluid, the pulps being formed by inspiss;ition of the latter, or by 

 development from the walls of the former. Neither Mr. Hunter nor Mr. Bell 

 has stited anything very definite on this subject The pulp must be con- 

 sidered as the principal part of the organ, and as the element which ap{)ear!) 

 first The sac is a mere subsidiary jwrt, supplied for purjwses of developuient 

 and nourishment. Handbach der Anatomic dts Mcnschai, von. H. Hilde- 

 bnmdt, besorgt. von K. H. Weber, Erster liand, p. "212; Handbuch dtr 

 Eiitwickelunijs-ij(schichle rfw MetiaJien, von Valentin, p. 4S2 ; Arnold, Salz- 

 bunj Mcdicinisdi-Chirurtfx^Ji Zeitung, 1831, Erster liand, p. 236 ; Cruveilhier, 

 Anatomu Descriptivf, vol. i. p. 518; Serres, Esstii stir I'Anatomu, etc., rf« 

 Dents, J). f>9 ; Ph. Fr. Hlandin, Anatomic du Sysieme DeiUairc, etc., p. 87 ; 

 Blake, Essay on the Human Ticth, p. 2. 



