In this group the segments are united by fibrous tissue or cartilage, or
a mixture of the two in such a manner as practically to preclude
movement; hence they are often termed fixed or immovable joints. There
is no joint cavity. Many of these joints are temporary, the uniting
medium being invaded by the process of ossification, with a resulting
ankylosis or synostosis. The chief classes in this group of joints are
as follows:
(1) =Suture.=—This term (Sutura) is applied to those joints in the skull
in which the adjacent bones are closely united by fibrous tissue—the
sutural ligament. In many cases the edges of the bones have irregular
interlocking margins, forming the =sutura serrata=, _e. g._, the frontal
suture. In others the edges are beveled and overlap, forming the =sutura
squamosa=, _e. g._, the parieto-temporal suture. If the edges are plane
or slightly roughened, the term =sutura harmonia= is applied to the
joint, _e. g._, the nasal suture.
(2) =Synchondrosis.=—In these the two bones are united by cartilage, _e.
g._, the joint between the basioccipital and the sphenoid bone. Very few
of these joints are permanent.
(3) =Symphysis.=—This term is usually limited to a few median joints
which connect symmetrical parts of the skeleton, _e. g._, symphysis
pelvis, symphysis mandibulæ. The uniting media are cartilage and fibrous
tissue. In some cases a cleft-like rudimentary joint cavity occurs.
(4) =Gomphosis.=—This term is applied to the implantation of the teeth
in the alveoli.