ii6 THE SURGICAL ANATOMY OF THE HORSE 



division arises beneath the superficial portion and resolves itself into two 

 bundles which run downwards and backwards to be inserted into the 

 inner aspect of the calcis and astragalus respectively. 



The deep division is by far the most delicate of the three, and 

 sometimes its fibres can only be made out with greatest difficulty. It 

 arises beneath the middle division and is inserted into the astragalus in 

 close proximity to the insertion of its astragaloid portion. This division 

 is enveloped by the synovial membrane of the joint. 



The anterior common ligament is sheet-like and somewhat mem- 

 branous. It closes the front of the tibio-tarsal joint. Its fibres have 

 a peculiar intercrossed arrangement, the outer portion of the ligament 

 being much stronger than the inner. This is a point of surgical 

 importance, inasmuch as the appearance of the bulging in cases of bog 

 spavin in this situation is due to the weaker structure of the inner 

 portion of this ligament. Superiorly this ligament is attached to the 

 anterior face of the inferior extremity of the tibia. Inferiorly it is 

 attached to the astragalus, scaphoid, the two cuneiform bones, and to 

 the astragalo-metatarsal ligament. Through its fibres being confounded 

 with those of the ligament just mentioned, it obtains insertion also into 

 the large metatarsal bone. Its deep face is lined by the synovial 

 membrane of the true hock joint, to which membrane the ligament gives 

 support. Its superficial face is crossed by the tendons of the extensor 

 pedis and flexor metatarsi muscles, and also by the anterior tibial artery. 

 On this surface ramify also a number of veins, which unite with the 

 vein passing forwards through the cuboido-scaphoido-cunean canal, to 

 form the anterior tibial vein. 



The posterior common ligament is also sheet-like, and it closes 

 the tibio-tarsal joint posteriorly. It is attached superiorly to the 

 posterior aspect of the inferior extremity of the tibia, and inferiorly it 

 obtains insertion into the calcis and astragalus. This ligament is most 

 powerful towards its centre, where it presents a fibro-cartilaginous 

 thickening over which the tendon of the flexor perforans muscle plays. 



