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88 ANATOMY. —

accommodate. The socket for the central incisor tooth is nearly conical
in shape. That for the lateral incisor is conical, but smaller and more
compressed meso-distally than the central socket, and often presents a
slight distal curve at its upper extremity. The socket for the cuspid
(canine) tooth is conical in form, deeper and larger than those for the
incisors, and somewhat compressed, especially at its inner aspect, form-
ing an oval in transverse section. The sockets for the bicuspidati
resemble flattened cones, that for the first bicuspid generally bifurcating
at the upper portion, as this tooth frequently has two roots. The same
reason occasionally causes a bifurcation of the socket for the second
bicuspid. The sockets for the molar teeth are broad, and divided at
their upper three-fourths into three compartments. The socket for the
wisdom tooth is an exception to this formation, frequently not dividing
at all, and sometimes having more than three compartments.
The septa between the alveoli extend downward to a lower levei
than the plates composing the alveolar processes, so that their free
margins are convex—a point to be remembered in practical dentistry
in fitting permanent bands and metal crowns on roots that are embraced
in the alveolar walls.
Each alveolar wall consists of a shell of thin, compact bony structure
surrounded by spongy tissue. This shell comes into contact with the
dense cortical plates composing the surfaces of the bone, mainly at the
margin near the neck of the tooth. At the apical portion of the sockets
are small openings for the entrance of vessels and nerves supplying the
teeth.
The teeth are held in their sockets by alveolo-dental connective tissue.
It is elastic, and allows a considerable motion of the teeth. In the
dried bone the loss of this tissue loosens the teeth and permits their
detachment from the sockets.
Development.—The development of the superior maxillary bone
(Fig. 38) commences so early and increases with such rapidity that it is
difficult to mark out its line of growth. It arises in membrane from
many points of ossification, at least one each for the orbital plate, the
nasal process, and tiie alveolar border. These appear about the sixth
or seventh week of embryonal life, and soon coalesce. Hence these
parts are claimed by some to arise from one centre. They form the
lateral portion of the bone, which contains all the teeth except the two
incisors, and is called by comparative anatomists the true maxilla.
That portion of the bone which contains the central and lateral incisor
teeth arises from a separate point of ossification, and is known as the
premaxilla. In many of the lower animals it remains distinct from the
true maxilla throughout life.
When there is union between the two premaxillary bones in the
median line, but no lateial union between them and the true maxillae,
thev form the intermaxillary bone of the lower animals. In man the
premaxilla soon unites with the maxilla ]M'()per by a suture, which on the
facial surface may be seen until the sixth year, and on the hard palate
it generally remains until adult life. The suture on the hard palate
extends as fiu- back as the posterior portion of the anterior palatal canal.
In single or unilateral complete cleft palate i. e. the clefib extending