TRANSACTIONS OF THE SECTIONS. 149 



tubes, having a general direction perpendicular to the surface of the 

 tooth, and closely resembling true ivory. The pulp then, instead of 

 continuing to form similar tubular ivory, by adding to the extremities 

 of the previously formed tubes, became subdivided, or broken up into 

 numerous processes, to which those forming the three fangs of a hu- 

 man grinder are analogous. But each process here becomes the centre 

 of an active formation of similar branched tubes, radiating in all di- 

 rections from that centre, and anastomosing by their peripheral branches 

 with those from contiguous centres, or communicating with interposed 

 calcigerous cells. The cavities containing the above subdivisions of the 

 pulp, like the Haversian canals containing the processes of medulla in 

 true bone, have had their area diminished in like manner by the suc- 

 cessive formation of a series of concentric lamellae, traversed, as in 

 true bone, by radiating and minutely ramified calcigerous tubes, com- 

 municating with each other and with the minute cells in the inter- 

 spaces. The resemblance between the pulp canals of the teeth of 

 Acrodus and of the medullary canals of bones, is further exemplified 

 in the existence of lateral communications in teeth ; and in function as 

 well as structure they may be regarded as being identical. 



With reference to the application of the tubular structure of the 

 teeth to the explanation of their pathology, Professor 0\^'en observed, 

 that it was a new and fertile field, which would doubtless be replete 

 with interesting results, and might suggest some good practical im- 

 provements in dental surgery. Ordinary decay of the teeth com- 

 menced, in the majority of instances, immediately beneath the enamel, 

 in the fine ramifications of the peripheral extremities of the tubes, and 

 proceeded in the direction of the main tubes, and, consequently, by 

 the most direct route to the cavity of the pulp. The decayed sub- 

 stance, in some instances, retains the characteristic tubular structure, 

 which is also observable in the animal basis of healthy teeth after the 

 artificial removal of the earthy salts. The soft condition of the de- 

 cayed portion of a tooth is well known to all dentists ; it depends upon 

 the removal of the earthy salts from the containing tubes and cells, in 

 which process the decay of teeth essentially consists. The main ob- 

 ject of the dentist, in reference to ordinary caries of the teeth, seems, 

 therefore, to be, to detect those appearances in the enamel which in- 

 dicate the commencement of decay — to break away the enamel, whose 

 natural adhesion to the subjacent softened ivory will be found to be 

 more or less diminished — to remove the softened portion of the ivory 

 and fill up the cavity with incorrodible substance. Experience proves, 

 what could not be intelligibly explained before the true structure of 

 the dental substance was known, viz. that the progress of the decay is 

 sometimes thus permanently arrested. Such cases sometimes exhibit 

 a thin dense layer of ivory in contact with the stopping, apparently re- 

 sulting from an exudation of the calcareous salts from the extremities 

 of the tubes divided in the operation. 



In conclusion, Professor Owen passed in general review over the 

 structures which he had described in detail. He particularly pointed 

 out the important application of the microscopic examination of thin 



