1854.] OF THE ROYAL INSTITUTION. 365 
WEEKLY EVENING MEETING, 
Friday, February 10. 
Right Hon. Baron Parkes, Vice-President, in the Chair. 
Prorressor Owen, F.R.S. 
On the Structure and Homologies of Teeth. 
Tue Lecturer commenced by observing that, although the teeth 
were among the least vitalised of animal parts, and commonly 
possessed no power of repairing fracture or decay, they presented 
many phenomena of anatomical, physiological, and homological 
interest, a selection from which he proposed to offer as the sub- 
ject of the evening's discourse. 
Any hard body attached to the walls and projecting into the cavity 
of the mouth, where it is exposed to view when the mouth is 
open, is called a tooth: but the parts properly so called, are those 
which consist of a gelatinous basis, hardened by earthy salts, in 
which the phosphate of lime predominates. Such teeth are pecu- 
liar to the Vertebrate Classes. In them they present manifold 
varieties as to number, size, form, structure, position, and mode 
of attachment, but are principally adapted for seizing, tearing, di- 
viding, pounding, or grinding the food ; in some species they are 
modified to serve as formidable weapons of offence and defence ; 
in others as aids in locomotion, means of anchorage, instruments 
for uprooting or cutting down trees, or for transport and working 
of building materials ; they are characteristic of age and sex ; and 
in man they have secondary relations subservient to beauty, and to 
speech. 
Teeth are always intimately related to the food and habits of the 
animal, and are therefore highly interesting to the physiologist : 
they form for the same reason important guides to the naturalist 
in the classification of animals; and their value, as zoological 
characters, is enhanced by the facility with which, from their 
position, they can be examined in living or recent animals ; whilst 
the durability of their tissues renders them not less available to 
the paleontologist ia the determination of the nature and affinities 
of extinct species, of whose organisation they are often the sole 
remains discoverable in the deposits of former periods of the 
earth's history. 
Teeth are not of an uniform tissue or substance like bone: that 
which forms the body of the tooth is called “ dentine ;” the tissue 
which forms the outer crust is called ‘ cement ;” and in most 
Vertebrata a third substance is situated between the dentine and 
cement, called ‘‘ enamel.” The characteristics of these three 
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