11 
WEDNESDAY, FEBRUARY 15th, 1888. 
TEETH—THEIR STRUCTURE IN MEN AND. ANIMALS. 
Mr. WALTER HARRISON, D.M.D. (Harvard). 
' It is a common error to speak of teeth as bones. Teeth are 
not bones, but are developed from the skin, in other words they 
are dermal appendages and must be considered in the same 
category as hair and nails. In looking at the arrangement of 
human teeth in the jaws it may be noticed that no tooth is 
_ exactly over another one, and that there are no interspaces 
x between them. Each tooth is met by two teeth. In consequence 
_ of this the loss of a single tooth is not so severely felt. The 
q teeth are arranged around the margins of the maxillary bones in 
a curve which is somewhat parabolic in form. It is generally 
rounded after the manner of a Norman arch. In the lower races 
of mankind this becomes somewhat square owing to the 
prominence of the canine teeth. The tendency of civilization, 
however, is to make this curve sharper, in fact, somewhat of a 
Gothic arch. Its extreme shape, occasionally seen, is a V-shaped 
maxilla. 
. Some animals develop only one set of teeth, others two. 
In man the first set, milk-teeth, remain till about 7 years 
old. In the Ungulate they persist until the animal has reached 
adult age. 
ag The teeth in the Mammalia are built up of three different 
kinds of tissue, viz., Enamel, Dentine, and Cementum. The 
5 enamel of the tooth is the hardest tissue in the body, and 
lowest in organic matter. 
The principal substance, however of which teeth are composed 
‘is dentine. Sometimes this closely resembles bone in structure. 
In the Mammalia, it is permeated with tubes, which radiate from 
the pulp cavity, containing Tomes’s Fibrils ; it is by means of these 
q ih at it communicates with the blood-vessels, and nerves. The 
