FIG. 6.—THE NAVICULAR BONE (VIEWED FROM BELOW).
1, Inferior surface (smooth for the passage of the flexor perforans); 2, anterior edge of inferior surface; 3, posterior edge of inferior surface.
FIG. 7.—THE NAVICULAR BONE (VIEWED FROM ABOVE, THE BONE TILTED POSTERIORLY TO SHOW ITS ANTERIOR BORDER).
1, Superior articulatory surface; 2, anterior border (grooved portion of); 3, anterior border (articulatory portion of).
FIG. 8.—LIGAMENTS OF THE FIRST AND SECOND INTERPHALANGEAL ARTICULATIONS (VIEWED FROM THE SIDE). (AFTER DOLLAR AND WHEATLEY.)
1, Outermost slip from the glenoidal fibro-cartilage; 2, lateral ligament of the first interphalangeal articulation; 3, prolongations of the lateral ligament of the first interphalangeal articulation attached to the end of the navicular bone to form the postero-lateral ligament of the pedal joint; 4, end of the navicular bone; 5, antero-lateral ligament of the pedal joint.
The Lateral Ligaments.—These are large and thick, an outer and an inner, running obliquely from above downwards and backwards. Each is inserted superiorly into the lateral tubercle of the lower end of the first phalanx, and inferiorly to the side of the second phalanx, their most inferior fibres becoming finally fixed to the extremities of the navicular bone, where they form the postero-lateral ligaments of the pedal articulation. In front of the joint the extensor pedis plays the part of an additional ligament.
The Synovial Membrane.—This is limited in front by the tendon of the extensor pedis, on each side by the lateral ligaments of the joint, and behind by the glenoid fibro-cartilage. At this point it is prolonged upwards as a pouch behind the lower extremity of the first phalanx.
THE ARTICULATION OF THE SECOND PHALANX WITH THE THIRD, THE PEDAL, OR THE COFFIN JOINT.—This also is an imperfect hinge-joint, permitting only of flexion and extension, which movements are more restricted than in the previous articulation. Three bones enter into its formation: the second phalanx, the third phalanx, and the navicular bone. The lower articulatory surface is formed by the third phalanx and the navicular bone combined. To effect this the navicular is closely and firmly attached to the third phalanx by an interosseous ligament. The two bones, as one, are then connected to the second phalanx by four lateral ligaments, an anterior and a posterior on each side.
The Interosseous Ligament consists of extremely short fibres running from the extensively grooved portion of the anterior surface of the navicular bone to become attached to the os pedis immediately behind its articular surface.
The Antero-lateral Ligaments are attached by their superior extremities to the lateral surfaces of the second phalanx, and by their inferior extremities into the depressions on either side of the pyramidal process of the os pedis.