SUBDIVISION INTO THREE CLASSES. 185 



The sutura dentata (dens, a tooth) is so called from the tooth-like form of the 

 projecting articular processes, as in the suture between the parietal bones. In 

 the sutura serrata (serra, a saw), the edges of the two bones forming the articula- 

 tion are serrated like the teeth of a fine saw, as between the two portions of the 

 frontal bone. In the sutura limbosa (limbus, a selvage), besides the dentated pro- 

 cesses, there is 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. 

 Where the articulation is formed by roughened surfaces placed in apposition with 

 one another, it is termed the false suture, sutura notha, of which there are two 

 kinds, the sutura squamosa (squama, a scak), formed by the overlapping of two 

 contiguous bones by broad bevelled margins, as in the temporo-parietal or squa- 

 mous suture ; and the sutura harmonia (dptiv, to adapt), where there is simple 

 apposition of two contiguous rough bony surfaces, as in the articulation between 

 the two superior maxillary bones, or of the horizontal plates of the palate. 



Schindylesis (sx^v^o^, a Jissure) 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 

 laminae of another, 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 superior maxillary and palate bones. 



Gomphosis (yo/u<j>oj, a nail) is an articulation formed by the insertion of a conical, 

 process into a socket, as a nail is driven into a board, and is illustrated in the 

 articulation of the teeth in the alveoli of the maxillary bones. 



2. AMPHIARTHROSIS. MIXED ARTICULATIONS. 



Amphiarthrosis (o-p$i, on all sides, dpflpov, a joint) or Mixed Articulation. In this 

 form of articulation, the contiguous osseous surfaces are connected together by 

 broad flattened disks of fibro-cartilage, which adhere to the ends of both bones, as 

 in the articulation between the bodies of the vertebrae, and first two pieces of the 

 sternum ; or the articulating surfaces are covered with fibro-cartilage, partially 

 lined by sy no vial membrane, and connected together by external ligaments, as in 

 the sacro-iliac and pubic symphyses; both these forms being capable of -limited 

 motion in every direction. The former resemble the synarthrodial joints in the 

 continuity of their surfaces, and absence of synovial sac ; the latter, the diarthro- 

 dial. These joints occasionally become obliterated in old age : this is frequently 

 the case in the interpubic articulation, and occasionally in the intervertebral and 

 sacro-iliac. 



3. DIARTHROSIS. MOVABLE ARTICULATIONS. 



Diarthrosis (Sia, through, ZpOpov, a joint). This form of articulation includes the 

 greater number of the joints in the body, mobility being their distinguishing 

 character. They are formed by the approximation of two contiguous bony sur- 

 faces, covered with cartilage, connected by ligaments, and lined by synovial 

 membrane. The varieties of joints in this class have been determined by the kind 

 of motion permitted in each, and are four in number: Arthrodia, Enarthrosis, 

 Ginglyrnus, Diarthrosis Eotatorius. 



Arthrodia is that form of joint which admits of a gliding movement ; it is 

 formed by the approximation of plane surfaces, or one slightly concave, the other 

 slightly convex ; the amount of motion between them being limited by the liga- 

 ments, or osseous processes, surrounding the articulation, as in the articular 

 processes of the vertebras, temporo-maxillary, sterno-clavicular, and acromio-clavi- 

 cular, inferior radio-ulnar, carpal, carpo-metacarpal, superior tibio-fibular, tarsal, 

 and tarso-metatarsal articulations. 



Enarthrosis is that form of joint which is capable of motion in all directions. 

 It is formed by the reception of a globular head into a deep cup-like cavity (hence 

 the name ball and socket), the parts being kept in apposition by a capsular liga- 

 ment strengthened by accessory ligamentous bands. Examples of this form of 

 articulation are found in the hip and shoulder. 



