Synarthroses include all those articulations in which the surfaces of the bones are in almost direct contact, fastened together by intervening connective tissue and in which there is no appreciable motion, as in the joints between the bones of the skull, excepting those of the mandible.
There are three varieties of synarthrosis: sutura, gomphosis, and syndesmosis.
Sutura
Sutura is that form of articulation where the contiguous margins of the bones are united by a thin layer of fibrous tissue. This kind of joint is found in the skull only. When the margins of the bones are connected by a series of processes, and indentations interlocked together, the articulation is termed a true suture (sutura vera). Sutura vera is of three types sutura dentata, serrata, and limbosa.
The sutura dentata is so called from the tooth-like form of the projecting processes, as in the suture between the parietal bones. In the sutura serrata the edges of the bones are serrated like the teeth of a fine saw, as between the two portions of the frontal bone. In the sutura limbosa, there is besides the interlocking, a certain degree of bevelling of the articular surfaces, so that the bones overlap one another, as in the suture between the parietal and frontal bones.
When the articulation is formed by roughened surfaces placed in apposition with one another, it is termed a false suture (sutura notha). of which there are two kinds: the sutura squamosa, formed by the overlapping of contiguous bones by broad bevelled margins, as in the squamosal suture between the temporal and parietal, and the sutura harmonia, where there is simple apposition of contiguous rough surfaces, as in the articulation between the maxillae, or between the horizontal parts of the palatine bones.
Syndesmosis
A type of joint in which two bony components are joined directly by a ligament, cord or aponeurotic membrane.
Examples – The shaft of tibia joins shaft of fibula by a membrane. This syndesmosis allows slight amount of motion with movements of knee and ankle joints. Another example of syndesmotic joint is inferior tibio-fibular articulation. Here the bones are connected by an interosseous ligament.
Gomphosis
Gomphosis is articulation in which the surfaces of a bony components are adapted to each other like a peg in a hole. This is illustrated by the articulations of the roots of the teeth with the alveoli of the mandible and maxillae.
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