288 On the Teeth of the Ox, Sheep, and Pig, 
into the interior of the organ and so be all exposed to wear at the 
same time. These constituents differ, as will be hereafter shown, 
in the amount of their relative hardness, and therefore in their 
power to resist attrition. Here we see a simjile hut most ejfectual 
provision for mainlaininfj the row/heried surface of teeth. Such 
teeth are called compound, to distinguish them from tliose which 
have enamel on their external surfaces only. In a carnivorous ani- 
mal, as the dog, and an omnivorous one, as the pig, we find simple 
teeth ; but in grass-eaters, as the ox, compound teeth, so far at least 
as the molars. The most familiar example of a simple tootli is an 
incisor of the ox or sheep. The molar teeth of tlie pig might, 
perhaps, from their size and irregular wearing surfaces, be thought 
to be compound ; they are, however, of the same description as 
its incisors and tushes. The peculiarities of each kind, in so far 
as they have a practical bearing on the subject of dentition, will 
be hereafter explained. 
Each tooth of itself is divided into different parts. The 
annexed engraving, fc/. 1, gives a view of a perfectly-formed 
permanent incisor of an ox, removed from the jaw just as it was 
about to be cut; the "chisel form" of which, as a whole, is 
very apparent. 
The several parts of a tooth are the croion, neck, and fang. 
These are well seen in the example 
^* before us. Tlie crown is the broad or 
expanded portion above, marked a. It 
is that part Avhich is exposed to wear. 
Sometimes it is called the body of the 
tooth, from its constituting, in many 
animals, the main bulk of the organ. It 
will be observed that the crown gets 
thicker and narrower as we approach the 
neck — a circumstance which explains 
the alteration in the shape and size of a 
worn incisor of the ox, when compared 
Avith one recently cut. The neck is the 
contracted part marked B. It is the 
point of junction between the crown 
and the fang. In no teeth that 1 am 
familiar with is the neck so well marked as in the incisors of 
the ox. 
Usually, when a tooth is fully up, the gum is said to embrace 
its neck, and thus to assist in keeping it in its place. In the pro- 
gress of a tooth rising from its socket, the gum, however, will 
A — 
* Fig. 1. A perfectly developed permanent incisor of an ox. a, the crown; 
B, neck ; c, fang. Natural size. 
