The _first toe_, or digit, called the _great toe_, or _hallux_, is composed of three phalanges, or segments. The first segment, or basal phalanx is considered a rudimentary metacarpal bone; it is attached by a fibrous cartilaginous tissue to the inner posterior surface of the inferior extremity of the metacarpal bone just below the spur. The _second toe_, likewise composed of three phalanges, is directed forward. It articulates with the inner trochlea located on the inferior metacarpal bone. The _third toe_, made up of four phalanges, is the middle of the three forward toes. It articulates with the middle trochlea of the inferior extremity of the metacarpal bone. The _fourth toe_, is composed of five phalanges; it is, however, of approximately the same length as the third, the segments being shorter. The fourth or outer toe articulates with the outer trochlea of the distal extremity of the metacarpal bone. ARTHROLOGY =Kinds of Joints.=—Joints may be movable, immovable, or mixed. In _movable_, or _true joints_ the articular surface of each bone is covered by cartilage. The bones are held together by ligaments, the capsular one often surrounding the joint and enclosing the synovial membrane. In some joints there is a pad of fibrous cartilage interposed between the two articular cartilages. Such a pad, called a _meniscus_, adds to the elasticity and the free movement of the joint. Movable joints form the most numerous class; they are for the most part found in the limbs. In an _immovable joint_ there is only a thin layer of fibrous or cartilaginous material interposed between the bones. The fibrous layer of the periosteum of both bones unite to cover the connecting material and becomes attached to the same, thus serving as a ligament. If the connecting material is fibrous, the joint is called a _suture_; if cartilaginous, a _synchondrosis_. These joints are found in the skull and in the pelvis. The term _mixed_ is used with reference, not to the motion in joints, but to their structure, which partakes of the nature of both the movable and immovable. The bones are firmly joined by a strong interposed pad of fibrous cartilage to which also is adherent the ligaments of the joint. There are no capsular ligaments; the cartilaginous pad or disc is softer toward its center, where occasionally there may be one, or even two, narrow cavities. Authorities differ as to whether such cavities are lined by synovial membrane or not. Since there are really no frictional surfaces in such a joint, motion depends upon the flexibility of the disc. The joints between the vertebral centra afford the best illustration of the mixed class.