DISSECTION OF THE ANTERIOR LIMB. 53 



the proximal end of the os corona?. It is a ginglymus, or hinge joint, 

 and corresponds to the second joint of the human finger. 



Movements. — As with the joint last described, the only natural 

 movements kxq flexion and extension. 



Directions. — The tendon of the extensor pedis, which passes over 

 the front of the joint, should be cut and reflected downwards. This 

 will show that the tendon completes the joint in front, where it plays 

 the part of an anterior ligament, and supports the synovial membrane. 

 The lateral ligaments are next to be defined, and after these the 

 supplementary cartilaginous apparatus placed behind the joint. 



The Lateral Ligaments. Each of these stretches from the lower 

 extremity of the first phalanx on its lateral aspect, to be inserted into 

 the side of the os corona?, and beyond that point some of its fibres are 

 continued downwards and backwards as the postero-lateral ligament of 

 the second interphalangeal joint. 



The Glenoidal Fibro-Cartilage. This is a piece of fibro-cartilage 

 fixed at the posterior edge of the upper articular surface of the os 

 corona?. It serves to increase that surface, and its anterior face is 

 moulded on the lower articular surface of the first phalanx, while its 

 posterior face is smooth for the passage of the perforans tendon. Three 

 fibrous slips pass from it on each side, and are attached to the first 

 phalanx. The superficial inferior sesamoidean ligament is inserted into 

 it, and the terminal insertion of the perforatus tendon is blended with 

 it on each side. 



Synovial Membrane. This is supported in front by the extensor 

 tendon, and on each side by the lateral ligament. Posteriorly it lines 

 the glenoidal fibro-cartilage, and is prolonged upwards as a pouch behind 

 the lower extremity of the first phalanx (Plate 10, Fig. 2). 



THE COFFIN JOINT (PLATE 11). 



This, the second interphalangeal joint, has three bones entering into its 

 formation, viz., the os corona?, the os pedis, and the navicular bone. It 

 is a ginglymus, and corresponds to the first joint of the human finger. 



Movements. — Flexion and extension. 



It possesses an interosseous ligament, and two pairs of lateral ligaments. 



The Interosseous Ligament is composed of short fibres passing from 

 the inferior border of the navicular bone to the os pedis behind its 

 articular surface. 



The Antero-Lateral Ligaments. Each of these passes from the side 

 of the os corona? to be inserted into the excavation at the side of the 

 pyramidal process of the os pedis. 



The Postero-Lateral Ligaments. These seem to be the downward 

 continuations of. the lateral ligaments of the pastern-joint. Passing 



