THE JOINTS. 
The study of the articulation of the bones and the liga- 
ments holding them in place is known as syndesmology. 
There are three general classes of articulations: Synar- 
throses, or immovable joints; amphiarthroses, or joints 
with slight motion; and diarthroses, or joints freely mov- 
able. A synarthrodal joint is exemplified in the sutures be- 
tween the bones of the skull. The two surfaces of bone are 
separated by fibrous membrane only. An amphiarthrodal 
articulation occurs between the 
bodies of the vertebre and also in 
the union of the sacrum with the 
ilium. In the articulation of the 
vertebrae the contiguous surfaces 
of the bone are faced by flattened 
discs of fibrocartilage (Fig. 21). 
The diarthrodal articulation is 
exemplified in all joints allowing oe Cre ae 
free motion. Such joints are DIARTHRODAL JOINT. 
composed of the following parts: a7, Articulatory cartilage ; lg, 
: ligament; sn, synovial 
the ends of two bones having membrane; sy, synovial 
their contiguous surfaces covered aa A et cavity; t, 
with cartilage; a synovial mem- 
brane forming a short tube whose ends are closed by the 
cartilaginous articulating surfaces; and several ligaments 
varying in number from two or three to a dozen (Fig. 44). 
There are four kinds of the diarthrosis: the arthrodia, or 
gliding joint, which occurs between the bones of the carpus; 
the enarthrosis, or ball-and-socket joint, such as at the hip 
or shoulder; the ginglymus, or hinge joint, exemplified at 
the elbow and knee; and the rotatoria, or pivot joint, formed 
by the articulation of the axis and atlas. 
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