|Henry Gray (1825–1861). Anatomy of the Human Body. 1918.|
|3. Classification of Joints|
| The articulations are divided into three classes: synarthroses or immovable, amphiarthroses or slightly movable, and diarthroses or freely movable, joints.|
Synarthroses (immovable articulations).—Synarthroses include all those articulations in which the surfaces of the bones are in almost direct contact, fastened together by intervening connective tissue or hyaline cartilage, 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 four varieties of synarthrosis: sutura, schindylesis, gomphosis, and synchondrosis.
Sutura.—Sutura is that form of articulation where the contiguous margins of the bones are united by a thin layer of fibrous tissue; it is met with only in the skull (Fig. 296). 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); and of this there are three varieties: sutura dentata, serrata, and limbosa. The margins of the bones are not in direct contact, being separated by a thin layer of fibrous tissue, continuous externally with the pericranium, internally with the dura mater. 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 maxillæ, or between the horizontal parts of the palatine bones.
FIG. 296– Section across the sagittal suture. (See enlarged image)
FIG. 297– Section through occipitosphenoid synchondrosis of an infant. (See enlarged image)
Schindylesis.—Schindylesis is that form of articulation in which a thin plate of bone is received into a cleft or fissure formed by the separation of two laminæ in another bone, as in the articulation of the rostrum of the sphenoid and perpendicular plate of the ethmoid with the vomer, or in the reception of the latter in the fissure between the maxillæ and between the palatine bones.
Gomphosis.—Gomphosis is articulation by the insertion of a conical process into a socket; this is not illustrated by any articulation between bones, properly so called, but is seen in the articulations of the roots of the teeth with the alveoli of the mandible and maxillæ.
Synchondrosis.—Where the connecting medium is cartilage the joint is termed a synchondrosis (Fig. 297). This is a temporary form of joint, for the cartilage is converted into bone before adult life. Such joints are found between the epiphyses and bodies of long bones, between the occipital and the sphenoid at, and for some years after, birth, and between the petrous portion of the temporal and the jugular process of the occipital.