Page Fourteen 
THE SOUTH AUSTRALIAN NATURALIST 
July 1, 1948. 
SPECIAL MODIFICATIONS OF TEETH 
By Dr. T. D. CAMPBELL 
Comparative dental anatomy provides 
striking examples of modifications of tooth 
form and function which depart considerably 
from the primary usages of teeth. 
In general, the main functions of teeth 
are for prehension, incision or comminution 
of food. They are organs belonging to the 
digestive system. With some of the verte- 
brates, the function of their teeth may be 
limited completely, or almost so, to one main 
purpose. For example, in many fishes 
and reptiles, the use of teeth is solely for 
the prehension or seizing of prey. In some 
herbivorous animals, most of their teeth arc 
for the comminution of the large quantities 
of vegetable food they consume. 
The following are some examples of special- 
ised uses of teeth. 
The poison fangs of the highly poisonous 
snakes are a striking example of extreme 
specialisation. These teeth are virtually hypo- 
dermic syringes. A canal in the body of the 
tooth conveys the venom to an opening near 
the tip of the tooth, from which it is in- 
jected into the body of the snake’s victim 
during the action of biting. An interesting 
feature of this particular tooth modification 
is that various stages of this venom-convey- 
ing mechanism are represented according to 
the degree of venomousness of the snake. In 
the less poisonous kinds the actual canal is 
represented by a groove on the tooth surface; 
and again this groove varies in depth in 
different snakes according to venomousness. 
The tusks of the elephant are an example 
of teeth (with aid of the trunk) performing 
a function of transportation. Before the 
days of intense mechanisation of industry, 
this usefulness of the elephant was exploited 
quite considerably. The tusks have little 
direct function in the business of food hand- 
ling. 
The incisors of the rodents are specialised 
teeth which function, in the beaver for ex- 
ample, as carpenter’s tools. His lower in- 
cisors operate against the upper incisors like 
a double pair of chisels; and with them the 
beaver is able to cut down trees of quite 
appreciable size to build its home. Also 
these teeth are so constructed that in their 
usage the chisel edges are maintained in 
shape and sharpness. 
The long, downward-pointing, upper jaw 
tusks of the walrus have little to do directly 
with the job of handling food. He uses 
them to assist in hauling himself over the 
ice, and so might be termed organs of loco- 
motion. 
The incisors of many of the carnivores 
are rather smallish, insignificant teeth which 
are useless in the main carnivorous business 
of cutting and slicing flesh food. They are 
often used for toilet purposes — acting as a 
fur or hair comb. 
In man, besides the primary function of 
dealing with food — which function has de- 
teriorated considerably in the diet habits of 
civilised man — teeth also serve important 
usages in vocal articulation and cosmetic 
standards. 
All of which goes to show that some teeth 
have evolved along lines which lead a long 
way from the primary functions. 
Also in the specific job of dealing with 
food, Nature has designed some striking and 
effective examples in tooth form. 
In the highly specialised carnivorous denti- 
tion, the cheek-teeth are compressed in 
shape to blade-like forms, so that the row of 
lower teeth operates against the upper row 
just like the blades of a scissors. Excepting 
that these dental “blades’* are irregular, but 
very sharp along the cutting edge — not 
straight as in the scissors. Nevertheless the 
dental blades of the carnivore are exceed- 
ingly powerful and effective for slicing- 
through flesh food. 
Entirely opposite in form and function to 
the carnivorous molars and premolars are 
those of the specialised typical herbivorous 
dentition in which the posterior teeth have 
broad, flat grinding surfaces, with transverse 
ridges of enamel. With these, the lower 
teeth work against the uppers as a series of 
grinding mills, crushing and disintegrating 
the fibrous vegetable food of a herbivorous 
diet. 
One of Solomon’s songs poetically de- 
scribes teeth as being like a flock of sheep 
that are even shorn; St. Matthew warns of 
the gnashing of teeth. Observations in den- 
tal anatomy also reveal some interesting 
forms and uses of teeth. 
