Covering, Support, and Movement of the Body
, literally “seams,” occur only between bones of the skull
. Te wavy articulating bone edges interlock, and
the junction is completely ﬁlled by a minimal amount of very
short connective tissue ﬁbers that are continuous with the peri-
osteum. Te result is nearly rigid splices that knit the bones
together, yet allow the skull to expand as the brain grows dur-
ing youth. During middle age, the ﬁbrous tissue ossiﬁes and
the skull bones fuse into a single unit. At this stage, the closed
sutures are more precisely called
erally, “bony junctions.” Because movement of the cranial bones
would damage the brain, the immovable nature of sutures is a
sēz), the bones are connected ex-
ligament), cords or bands of
ﬁbrous tissue. Although the connecting ﬁbers are always longer
than those in sutures, they vary quite a bit in length.
Te amount of movement allowed at a syndesmosis de-
pends on the length of the connecting ﬁbers. If the ﬁbers
are short (as in the ligament connecting the distal ends
of the tibia and ﬁbula, Figure 8.1b), little or no movement
is allowed, a characteristic best described as “give.” If the
ﬁbers are long (as in the ligament-like interosseous mem-
brane connecting the radius and ulna, Figure 7.28, p. 231), a
large amount of movement is possible.
is based on the amount of move-
ment allowed at the joint. On this basis, there are
joint), which are
on both sides), slightly movable joints; and
through, apart), or freely movable joints.
Freely movable joints predominate in the limbs. Immovable and
slightly movable joints are largely restricted to the axial skeleton.
Tis localization of functional joint types is understandable be-
cause the less movable the joint, the more stable it is likely to be.
In general, ﬁbrous joints are immovable, and synovial joints
are freely movable. However, cartilaginous joints have both rigid
and slightly movable examples. Since the structural categories are
more clear-cut, we will use the structural classiﬁcation in this dis-
cussion, indicating functional properties where appropriate.
Describe the general structure of ﬁbrous joints. Name and
give an example of each of the three common types of
, the bones are joined by ﬁbrous tissue, namely
dense ﬁbrous connective tissue, and no joint cavity is present.
Te amount of movement allowed depends on the length of the
connective tissue ﬁbers uniting the bones. Most ﬁbrous joints
are immovable, although a few are slightly movable. Te three
types of ﬁbrous joints are
Joint held together with very short,
interconnecting fibers, and bone edges
interlock. Found only in the skull.
Joint held together by a ligament.
Fibrous tissue can vary in length, but
is longer than in sutures.
“Peg in socket” fibrous joint. Periodontal
ligament holds tooth in socket.