THE HOCK JOINT 117 



The anterior surface of the hgament is lined by, and gives support to, 

 the synovial membrane of the joint. 



Its posterior face forms the upper portion of the anterior boundary 

 of the tarsal sheath, by the synovial membrane of which it is 

 covered. Laterally its fibres are commingled w^ith the posterior fibres of 

 the superficial division of the external and internal lateral ligaments 

 respectively. 



The Synovial Membranes. — Of the synovial membranes of the tarsus 

 the one which belongs to the tibio-astragaloid articulation or true 

 hock joint is much the largest and is also the most important. In 

 front it is supported by the posterior face of the anterior common 

 ligament. Behind it is similarly supported by the anterior face of 

 the posterior common ligament. Towards the inner side of the joint 

 it will be found to line the greater portion of the superficial, middle, 

 and deep divisions of the internal lateral ligament, whilst the deep 

 division of the external lateral ligament affords support to the 

 membrane outwardly. The synovial membrane of the true hock joint 

 sends a small diverticulum which supplies the upper articulation 

 formed between the calcis and astragalus, and it communicates with 

 the synovial capsule which supplies the intertarsal joint. The 

 arrangement of the synovial membrane of the tibio-astragaloid joint 

 is of great importance. This is the membrane which is concerned 

 in bog spavin and articular thoroughpin. 



The intertarsal synovial membrane supplies the joint formed 

 between the calcis and astragalus as representing the upper row of 

 bones, and the cuboid and scaphoid regarded here as the lower row. It 

 sends an upward prolongation to supply the more inferior of the 

 articulations formed between the calcis and astragalus, whilst the 

 anterior articulation formed between the cuboid and scaphoid is 

 supplied by a prolongation of this membrane. 



A third principal synovial membrane of the tarsus is the tarso- 

 metatarsal, and as its name implies this membrane supplies the joint 



