20 ON THE OHIGIN AND DEVELOPMENT OF THE 



similar to that of those at the fourth month ; but the gelatinous 

 granular substance between the pulp and the sac was of the 

 consistence of very firm jelly, closely and intimately adherent 

 to the whole interior of the sac, with the exception of a narrow 

 etrip all round the base of the pulp, along which strip the 

 grey membrane of the sac retained its original appearance, 

 and through which the radiating saccular twigs were visible, 

 being strongly and beautifully contrasted with the cream- 

 coloured surface of the granular substance. The mass of the 

 granular substance had a peculiar greyish-white colour ; its 

 surface was cream-coloured, and had a dry chalky appearance. 

 It had a tendency to tear in a direction perpendicular to the 

 internal surface of the sac. Although closely applied, it did 

 not adhere to the pulp, but, as stated above, surrounded it on 

 all sides tiU within a short distance of its base — " whatever 

 eminences or cavities the one had, the other had the same, 

 but reversed, so' that they were moulded exactly to each other." 

 In the incisives its principal mass lay " against the hollowed 

 inside of the tooth, and in the molars it was placed directly 

 against their base like a tooth of the opposite jaw." In the 

 pulps of the molars, which had three canals which now passed 

 completely across their bases, the granular substance sent a 

 process into each of them. These processes did not meet in 

 the centre, but disappeared near to it, and left, as in the case 

 of the general mass, a minute portion of the grey membrane 

 of the sac between themselves and the secondary bases of the 

 pulp.* In the case of the molars also the dental arterial 



* The only aixthors, as far as I know, who have observed and described 

 this gelatinous body, are Mr. Hunter in his Natural History of the Teeth, p. 94, 

 and Purkinje and Easchkow, in the work of the latter, entitled, Meletemata 

 circa Mammalium dentium evolutionem. Not having been able, hitherto, to 

 procure Easchkow's work, I can only state from Burdach {Physiologic, French 

 ed. torn. iii. p. 498), that Purkinje's opinion appears to coincide with Mr. 

 Hunter's as to its being the organ which secretes that enamel. Mr. Hunter 

 has not described the processes which this body sends under the pulp, or the 



