262
UNIT TWO
processes. Such a suture is in the adult human skull
where the parietal and occipital bones meet to form the
lambdoid suture. They are immovable, so sutures are
synarthrotic (sin
ar-thro
tik) joints
(f
gs. 8.2
and
8.3)
.
3.
Gomphosis
(gom-fo
sis). A gomphosis is a joint formed
by the union of a cone-shaped bony process in a bony
socket. The peglike root of a tooth fastened to a maxilla
or the mandible by a
periodontal ligament
is such a
joint. This ligament surrounds the root and F
rmly
attaches it to the bone with bundles of thick collagenous
F
bers. A gomphosis is a synarthrotic joint
(f g. 8.4)
.
PRACTICE
1
What is a joint?
2
How are joints classif
ed?
3
Describe three types oF f
brous joints.
4
What is the Function oF the Fontanels?
Cartilaginous Joints
Hyaline cartilage or F brocartilage connects the bones of
car-
tilaginous
(kar
tı˘-laj
ı˘nus)
joints.
The two types are
1.
Synchondrosis
(sin
kon-dro
sis). In a synchondrosis,
bands of hyaline cartilage unite the bones. Many of
these joints are temporary structures that disappear
during growth. An example is an immature long bone
where a band of hyaline cartilage (the epiphyseal plate)
connects an epiphysis to a diaphysis. This cartilage
band participates in bone lengthening and, in time,
is replaced with bone. When ossiF
cation completes,
usually before the age of twenty-F
ve years, the joint
becomes a
synostosis,
a bony joint. The synostosis is
synarthrotic (see F
g. 7.11).
Another synchondrosis lies between the manubrium
and the F
rst rib, directly united by costal cartilage
(f g. 8.5)
. This joint is also synarthrotic, but permanent.
connective tissue called a
sutural ligament.
Recall from
chapter 7 (p. 216) that the infantile skull is incompletely
developed, with several of the bones connected by
membranous areas called
fontanels
(see F
g. 7.31).
These areas allow the skull to change shape slightly
during childbirth, but as the bones continue to grow, the
fontanels close, and sutures replace them. With time,
some of the bones at sutures interlock by tiny bony
Connective tissue
(a)
(b)
Margin of
suture
Parietal
bone
Suture
Sutural
bones
Occipital
bone
(a)
(b)
FIGURE 8.2
±ibrous joints. (
a
) The f
brous joints between the bones
oF the skull are immovable and are called sutures. (
b
) A thin layer oF
connective tissue connects the bones at the suture.
FIGURE 8.3
Cranial sutures. (
a
) Sutures between the parietal and occipital bones oF the skull. (
b
) The inner margin oF a parietal suture. The grooves
on the inside oF this parietal bone mark the paths oF blood vessels near the brain’s surFace.
previous page 292 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 294 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off