OF SOFT TISSUE IN THE DENTINAL TUBES. 
52 i 
EXPLANATION OF THE PLATE. 
PLATE XXI.’^ 
Fig. 1. A section from the crown of the tooth of an adult made in a plane with the 
direction of the dentinal tubes, and afterwards decalcified and then torn 
in a line transverse to the direction of the tubes : (a) the dentine ; (b) the 
torn edge with the dentinal fibril (c) extending from the tubes. 
Fig. 2. A section made with a knife from the edge of the pulp-cavity of an adult 
tooth, including a portion of the pulp : (a) the dentine ; (b) the pulp with 
the peripheral cells arranged in lines ; (c) the dentinal fibrils drawn out of 
the displaced dentine ; (d) fibrils which pass through the fragment of 
dentine, and appear on the surface furthest removed from the pulp. 
Fig. 3. A section from dentine softened by caries, showing the consolidated dentinal 
tubes and fibrils cut transversely. 
Fig. 4. A section in a plane with the tubes, from carious dentine, showing consolida- 
tion of the fibrils, some of which are seen projecting from the edge of the 
specimen, while others have been broken within the tubes and are dis- 
placed. 
ADDENDUM. 
Received June 18, 1856. 
Since the preceding communication has been in the possession of the Royal Society, 
the head of a marsupial animal which had been preserved in spirit was placed at my 
disposal, the teeth of which were in a condition favourable for showing the dentinal 
fibrils, should such be found to exist. 
A paper upon the structure of the dental tissues of Marsupiata will be found in 
the Philosophical Transactions, Part II. 1849, in which the continuation of the den- 
tinal tubes into the enamel is described and figured; together with those minor 
differences of structure which are peculiar to the several divisions of this order of 
Mammalia. 
After the discovery of the dentinal fibrils, the examination of a favourable speci- 
men of enamel so peculiarly constituted became a matter of considerable interest, in 
order to ascertain whether the soft tissue which occupies the dentinal tubes is con- 
tinued into those of the enamel. I am indebted to my friend Professor Quekett for 
the jaws of Halmaturus , a member of a genus in which the majority of the den- 
tinal tubes situated in the crown of the tooth are continued into the enamel, and 
pass to within a short distance of the external surface of that tissue. Thin sections 
were made both of the incisor and molar teeth by the usual process of grinding. 
