Biomedical Engineering Reference
In-Depth Information
provide canals (foramina) for nerves to exit, and have flat bodies and
other processes for joint formation, designed for extreme forms of
movement yet bearing substantial amounts of weight. (For example,
the lumbar region houses interlocking articular processes that allow
an athlete to form the vital strong arch.) Irregular bones also have
processes such as the spinous processes (the backbone, which one
can see posteriorly) and transverse processes that allow muscles to
attach and permit localized rotations.
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Pneumatic bones.
Pneumatic bones, also called hollow bones, are
hollow or contain many air cells—for example, the mastoid part
of the temporal bone. Generally, pneumatic bones can also be cat-
egorized as irregular bones because of their irregularity in shape.
There is a difference between the two types, however, that is very
important, and for that reason they are often classified separately.
The characteristic difference is the presence of large air spaces in
these bones, which makes them lightweight. Pneumatic bones form
the major portion of the skull in the form of the sphenoid, ethmoid
(Figure 1.4), and maxilla. In addition to making the skull light in
weight, they also contribute to the resonance of sound and function
as air-conditioning chambers for inspired air.
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Sesamoid bones.
Sesamoid bones are usually short or irregular,
embedded in tendon and joint capsules. They have no periosteum
and ossify after birth. They are related to an articular or nonarticu-
lar bony surface, and the surfaces of contact are covered with hyaline
cartilage and lubricated by a bursa or synovial membrane. The most
obvious example of sesamoid bone is the patella (kneecap) which
sits within the quadriceps tendon (Figure 1.5). Other sesamoid bones
FIGURE 1.4
Illustration of ethmoid bones (http://www.learnbones.com/skull-cranial-and-facial-bones-
anatomy; accessed March 2011).
