86 THE ANATOMY OF THE HORSE. 



the fibula is opposed to the rough diarthrodial facet on the external 

 tuberosity at the upper end of the tibia, short and strong peripheral 

 fibres pass between the two bones, and bind them closely together. An 

 interosseous membrane extends across the tibio-fibular arch, and is perfor- 

 ated by the anterior tibial vessels. Just above the aperture for the 

 transmission of these vessels the fibres of the ligament are disposed in 

 opposite directions, like the limbs of the letter X. 



Where the osseous substance of the fibula ceases, a fibrous cord begins, 

 and this is carried downwards to the region of the external tuberosity 

 at the lower end of the tibia, where it mixes its fibres with the external 

 lateral ligament of the tibio-tarsal joint. 



THE TABSUS (fIG. 5). 



Several articulations are formed in the tarsus, or hock ; and these 

 are of very imequal importance as regards the amount of movement 

 permitted. The most important of them is that corresponding to the 

 ankle-joint of man, which is formed between the astragalus and the 

 lower extremity of the tibia ; and attention should first be given to the 

 movements that take place here. This is one of the most typical 

 ginglymoid joints in the body, the movements being limited to fi,exion 

 and extension. It will be observed that in flexion the distal part of the 

 limb does not move in the plane of the leg, but deviates a little out- 

 wards, and that in extension the movement is arrested by tension of 

 the lateral ligaments before the distal portion of the limb is brought 

 into the same straight line as the leg. 



In the other articulations found in connection with the tarsus the 

 movements are of a very restricted character, and are not concerned in 

 the general movements of the limb. They, however, serve a no less 

 important purpose in the joint, distributing and equalising pressure, 

 and obviating the bad effects which concussion would have been likelj 

 to produce in the tarsus, had it been one rigid structure. 



Directions. — The ligaments of the tarsus are both numerous and com 

 plicated, and the best order of their dissection is that in which they ar* 

 hereafter described. Since one set of ligaments must be removed ir 

 order to expose the following set, the dissector should not proceed witl 

 undue rapidity. 



TiBio-TARSAL LiGAMENTS. — These are four in number, viz., two lateral 

 an anterior, and a posterior. 



The External Lateral Ligament consists of a superficial and a dee] 

 fasciculus, which cross one another like the legs of the letter X. Th 

 superficial division, which is the larger of the two, is fixed superiorl; 

 to the posterior part of the external tuberosity at the lower en( 

 of the tibia, while inferiorly its fibres are inserted into the astrag 

 alus, OS calcis, cuboid, large metatarsal bone, and external smal 



