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112 ANATOMY.

would be called harmonic, no matter under what head they might be
classed externally.
The Syxchondeoses are almost immovable articulations. A thin
layer of cartilage intervenes between the intercartilaginous bones which
go to form this articulation, uniting them together. It is found between
the epiphyses and shafts of long bones. Examples, the occipito-sphe-
noidal articulation and the articulations of the liyoid bone at the cornua.
The Diarthroses.—The greater number of the joints of the body
are of this variety. These articulations have extensive movement, such
as is seen in the elbow, knee, shoulder, hip, and temporo-maxillary
joints. The articulating surfaces of these bones are either convex or
concave, and covered by a thin layer of cartilage, forming a smooth
articulating extremity. Synovial cavities also exist between the ex-
tremities of the bones forming these joints, which are further lubricated
by a synovial fluid secreted by a delicate membrane lining all the inter-
nal portions of the joints excepting the cartilaginous, though it invests
the borders of the cartilages interp(jsed between the joints and assists in
holding the bones in apposition. In some joints interarticular discs of
iibro-cartilage are placed between the articulating surfaces of bones
composing them, these discs dividing the space into two compartments
of dissimilar size. An example of this is seen in the temporo-maxil-
lary articulation.
Articulating surfaces are also often marked by irregular facets, so that
when the bones are at diiferent degrees of flexion and extension in the
joint-cavity there is a special articulating point for that particular posi-
tion. The opposing surfaces of bones forming these joints are held in
apposition by fibrous tissue of various shapes as well as by synovial
membrane. This fibrous tissue receives its name according to its
relation with the joint. For example, the crucial ligaments of the
knee receive their name because they cross each other (obliquely), while
the capsular ligaments of joints are so named because they surround the
joints.
Tlie diartlirodial articulation is variously subdivided. Gray speaks
of f )ur divisions—viz. Arthr(xlia, Enarthrodia, Ginglymus, and Diar-
thnxlia Rotatoria ; while Allen recognizes five divisions—the Arthro-
dial, Spherical, Cylindrical, Conical, and Composite. Here it will be
necessary only to describe the combination of these subdivisions which
covers the movements of the temporo-maxillary joint.
The T('iiijjoro-in(fxi//fin/ Articulation.'^ are formed by the union of the
condyloid processes of the inferior maxilla with the anterior porticms of
the glenoid fossfe of the temporal bones, the glenoid fissures being imme-
diately behind the condyles, while the eminentise articularise are in
front.
Gray descrilx>s the arthrodial as "that form of joint which admits of
a gliding movement, .... the amount of nioticm between them being
limited by the ligaDicnts or osseous processes surrounding the articula-
tion, as in the articular processes of the vertebrae, the temporo-maxillary,
sterno-clavicular, and acromio-clavicular," etc. etc.
Allen describes the ginglymus or hinge-joint, which is a subdivision
of the cylindrical division of diarthrotic joints, as the '' best expression