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.

The Postero-lateral Ligaments.—­As mentioned when describing the first interphalangeal articulation, these are in reality continuations of the lateral ligaments of that joint.  Running obliquely downwards and backwards from their point of attachment to the first phalanx they curve round the lower part of the side of the second phalanx and end on the extremities and posterior surface of the navicular bone.  Having reached that position, they send short attachments to the retrossal process of the os pedis and to the inner face of the lateral cartilage.

[Illustration:  FIG. 9.—­LIGAMENTS OF THE FIRST AND SECOND INTERPHALANGEAL ARTICULATIONS (VIEWED FROM BEHIND). (AFTER DOLLAR AND WHEATLEY.) 1, Suspensory ligament; 2, innermost slip from complementary cartilage of pastern joint; 3, middle slip from complementary cartilage of pastern joint; 4, outermost slip from complementary cartilage of pastern joint; 5, glenoid or complementary cartilage of pastern joint; 6, postero-lateral ligaments of the pedal joint; 7, the navicular bone; 8, interosseous ligaments of the pedal joint; 9, semilunar crest of os pedis; 10, plantar surface of os pedis.]

Synovial Membrane.—­This extends below the facets uniting the navicular to the pedal bone, and offers for consideration two sacs.  A large one posteriorly running up behind the second phalanx to nearly adjoin the sesamoidean bursae, and a small one, a prolongation of the synovial membrane between the antero-lateral and postero-lateral ligaments of the same side.  This latter is often distended, and on account of its close proximity to the seat of operation, is liable to be accidentally opened in excision of the lateral cartilage for quittor.