DISSECTION OF THE POSTERIOR LIMB. 87 



fibro-cartilage. Although these insertions serve to prevent the total 

 displacement of the fibro-cartilages, some degree of movement is, never- 

 theless, permitted to the latter ; for it will be noticed that during flexion 

 they are, as it were, squeezed towards the front of the joint, while in 

 extension they are carried backwards. 



Directions. — If the internal lateral ligament be now cut, and the in- 

 ternal condyle removed with the saw, a better view will be obtained of 

 the crucial ligaments ; after which, complete separation of the femur and 

 tibia should be effected by cutting the remaining lateral ligament, tlje 

 crucial ligaments, and the slip of insertion of the external fibro-cartilage 

 at the back of the intercondyloid groove. This will expose thoroughly 

 the semilunar fibro-cartilages. 



Tibio-fibular Articulation. In the horse the amount of movement 

 permitted between the bones of the leg is very restricted, and not 

 appreciable on the general movements of the limb. Where the head of 

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

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

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

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

 forated 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 

 malleolus of the tibia, where it mixes its fibres with the external 

 lateral ligament of the tibio-tarsal joint. 



THE TARSUS (FIG. 5.) 



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

 are of very unequal 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 flexion 

 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, 



