■iZ THE ANATOMY OF THE HOKSE. 



ligament, and on each side by the hiteral ligament. Behind the joint 

 it is supported below the sesamoids by the deep inferior sesamoidoan 

 ligament, but above these bones it is unsupported ; and when the 

 synovial sac is distended, it bulges iip wards between the branches of 

 the suspensory ligament (Fig. 1, page 33). 



THE PA.STERN-JOINT (PLATE 11). 



This joint, which is technically termed the ^tirst interphalangeat 

 articulation, is formed between the distal end of the os suffraginis and 

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

 and con-esponds to the second joint of the human finger. 



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

 movements are Jlej.ion 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 sujiports 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 coronte, and beyond that point some of its fibres are 

 continued downwards and backwards as the postero-latcral 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 

 coronae. It serves to increase that surfoce, and its anterior ftice 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 j^ass 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 coronre, the os i)cdis, and the navicular bone. It 

 is a ginglymus, and corresponds to the fii-st joint of the human finger. 



Movements.— /V^.r?c»?i and extension. 



