62 THE SURGICAL ANATOMY OF THE HORSE 



patella is attached. The middle straight patellar ligament is attached to 

 the groove mentioned. 



The external tuberosity is articular on its superior aspect, where it 

 presents a large facet which is usually described as being saddle-shaped. 

 It articulates indirectly with the external condyle of the femur, the outer 

 semilunar disc being interposed between the two bones. On the outer 

 side of this tuberosity, below its articular surface, is a roughened 

 depression, to which the head of the fibula is articulated. 



The superior aspect of the internal tuberosity is also articular. For 

 the most part it is almost flat, but inwardly it extends upwards on the 

 inner surface of the tibial spine. Upon this surface the inner semilunar 

 disc rests, the upper surface of which articulates with the internal 

 condyle of the femur. On its posterior aspect, and towards the middle 

 line of the bone, this tuberosity presents, slightly below the level of its 

 articular surface, a small tubercle, to which the posterior crucial ligament 

 is attached. 



The tibial spine is an upwardly-projecting, peak-like process placed 

 near the middle of the upper extremity of the bone. As already stated, 

 the articular surface of the internal tuberosity is continued upwards on the 

 inner surface of the spine. Its outer surface is roughened, and affords 

 attachment to the anterior crucial ligament. 



On the roughened areas between the tuberosities will be seen a large 

 number of small foramina, which transmit the vessels of the cancellated 

 tissue. 



The inferior extremity presents on its lower surface an articular area 

 for the astragalus. On this area are two deep grooves, which take a 

 direction outwards and forwards. They are separated from one another 

 by a prominent articular ridge. The ridge and grooves articulate with 

 the groove and ridges of the astragalus, thus forming the true hock joint. 



Each groove is bounded excentrically by a large tuberous piece of 

 bone termed a malleolus. The external malleolus is smooth and articular 

 inwardly where it bounds the outer groove. Outwardly it is convex 



