BIOLOGICAL AND MI0K0S00PICAL DEPARTMENT 



OF THE 



ACADEMY OF NATURAL SCIENCES. 



Jan. Bd, 1870. 

 Director S. W. Mitchell, M.D., in the Chair. 



Eighteen members present. 



Dr. McQuillen exhibited the skull of a hedge-hog, in which, owing to 

 fracture of the left lower incisor, the superior incisor of that side, failing to 

 meet with its antagonist, had formed a complete circle, the apex of the 

 tooth penetrating the right upper maxilla just in front of the molars. The 

 right upper incisor also had been fractured, and the inferior incisor of thai 

 side had grown to more than twice the usual length, and assumed the form 

 of a tusk. The skull of a squirrel was also shown, in which, owing to a 

 similar accident, the superior incisors had formed a complete circle and 

 penetrated the upper maxilla. 



Jan. 17th. 

 Director S, W. Mitchell, M.D., in the Chair. 

 Fourteen members present. 



Dr. McQuillen exhibited the pulp of a lower molar, with the vessels natu- 

 rally injected. The principal points of interest connected with the specimen 

 were the dentinal fibrili, which were quite evident under the microscope, 

 projecting from a fragment of dentine. In commenting on the specimen, the 

 speaker stated that these fibrili, which are located in the dentinal tubuli, were 

 first observed some eight or ten years ago in the human teeth by John Tomes, 

 F.R.S., of London, who regards them as the continuation of the nerves of the 

 dental pulp, and accounts for the exquisite sensibility of tiie dentine in exca- 

 vating decay from the cavity of a tooth, by impressions made upon these fila- 

 ments. The speaker would not pretend to assert that this was an untenable 

 position, but he inclined to the opinion that the dentinal fibrili are to be re- 

 garded as post mortem results occurring after the extraction of a tooth, and 

 due to the coagulation of the fibrine of the liquor sanguinis circulating in the 

 dentinal tubuli during life. In the removal of pulps from the teeth when de- 

 vitalized by arsenical application, or breaking up a tooth alter extraction, he 

 had found no difficulty in separating the pulp from the dentine, which would 

 hardly be possible if the nerve fibres passed into the millions of tubuli in the 

 dentine, or under such circumstances an attachment would be tunned ex- 

 ceedingly difficult of separation. 



A large plaster model of an incisor tooth, with a vertical section Bhowing 

 the arrangement of the enamel, cementum, dentine, pulp cavity and pulp, un- 

 used in illustration of the remarks. 



