28o A MANUAL OF ANATOMY 



the superior maxillae. In the grooved suture a ridge on one bone 

 is received into a cleft on another. Such a suture is known as 

 schindylesis, and it is exemplified in the articulation between the 

 rostrum of the sphenoid and the vomer. 



Amphiarthrosis.-;-In this class the opposed surfaces are connected 

 either by a disc of fibro-cartilage, or by an interosseous ligament, 

 and the joint is partially movable. When the connecting medium 

 is a disc of fibro-cartilage the name of symphysis is given to the joint, 

 as between the bodies of the vertebrae, the bodies of the pubic bones, 

 and between the presternum and mesosternum. When the con- 

 necting medium is an interosseous ligament the joint is called syndes- 

 mosis, as in the inferior tibio-fibular articulation. Union by means 

 of an interosseous membrane is also a form of syndesmosis. 



Diarthrosis. — While there is more or less continuity at a syn- 

 arthrosis and an amphiarthrosis, there is none at a diarthrosis. The 

 articular ends of the bones are free, and the joint is freely movable. 

 The ends of the bones are smooth and polished, being covered by 

 articular cartilage; they are connected by ligaments; and the 

 interior of the joint is lined with a synovial membrane, except over 

 the articular cartilages. This membrane secretes the synovia, 

 which lubricates all parts of the interior. There are five varieties 

 of diarthrosis. 



1. Enarthrosis or Ball-and-socket Joint. — In this variety one 

 articular end is spherical, and the other is hollowed into a socket 

 for its reception, as in the shoulder- and hip-joints. 



2. Condylarthrosis or Condylar Joint.— This is akin to enarthrosis. 

 One articular end has the form of a condyle, and the other presents a 

 shallow cavity, as in the metacarpo- and metatarso-phalangeal joints. 



3. Trochlearthrosis, Ginglymus, or Hinge Joint.— In this variety 

 one articular end has the form of a trochlea or pulley, and the other 

 is so shaped as to adapt itself to it, as in the elbow- and ankle-joints. 



4. Arthrodia or Gliding Joint. — In this joint the surfaces are almost 

 plane, or in some cases concavo-convex, as in the joints between 

 the articular processes of vertebrae, and the carpal and tarsal joints 

 Under this variety is to be included the reciprocal or saddle joint, 

 where the articular surfaces are saddle-shaped and mutually adapt 

 themselves to each other, as between the trapezium and the first 

 metacarpal bone. 



5. Trochoides or Pivot Joint. — In this joint one articular end 

 forms a pivot, and the other is so arranged as to rotate around it, as 

 between the atlas and the odontoid process of the axis. 



Ligaments. — These are composed of white fibrous tissue, and, as 

 their name implies, they bind the bones together. At a diarthrosis 

 their chief use is to control movement, the bones being maintained 

 in position by the muscles and atmospheric pressure. At their attach- 

 ments they are intimately associated with the periosteum. When the 

 fibrous tissue is arranged continuously round the joint the ligament 

 is called a capsular ligament. In other cases the tissue is disposed 

 as round cords, and in a third variety it forms flattened bands. 



