HOCK JOINT. 379 
but not so large as, and thinner than, the preceding. Its inferior extremity 
is attached to the internal side of the anterior tuberosity of the tibia. Its 
superior extremity, much thickened, becomes fibro-cartilaginous, and is 
inserted in the projection on the inner and upper border of the patella. 
The middle ligament, a rounded cord (situated, as its name indicates, 
between the two preceding ligaments), covers and assists in protecting the 
synovial capsule in front. 
Movements.— During flexion and extension, which are the chief motions 
permitted, the semilunar fibro-cartilages which are fixed on the superior 
tibial surfaces, transforming them into glenoid cavities, move upon the 
condyles of the femur, from before backwards, or from behind forwards, 
according to the movement executed. But at the same time they glide, in 
a very appreciable manner, upon the superior extremity of the tibia. 
Thus, at the time of flexion, they move from behind forwards upon this 
extremity, and are brought backwards during extension. Rotation takes 
place from within to without, or vice versd, and is produced not only by 
the first movement of the condyles in their glenoid cavities, but by the 
displacing of the semilunar cartilages on the superior extremity of the 
tibia. 
TIBIO-FIBULAR ARTICULATION. 
THIS ARTICULATION is formed by the union of the little arthrodial spot, 
found at the internal surface of the head of the fibula, with a cor- 
responding surface upon the external and superior tuberosity of the tibia. 
Short and strong fibres envelop these surfaces on the sides, and keep 
them firmly in contact. The fibula is again attached to the tibia—Ist, 
above, by little ligamentous bundles, crossed in the shape of an X, which 
form the superior part of the arcade, or bridge, formed between the tibia 
and fibula; 2d, in the middle, by a sort of aponeurotic membrane, of 
which the breadth diminishes from above downwards, like that of the 
interval which it fills; 3d, below, by a ligamentous band, which joins 
the fibula to the external tuberosity of the inferior extremity of the tibia, 
where this cord divides and unites with the two external lateral ligaments 
of the tibio-tarsal articulation. 
THE MOVEMENTS of this articulation are very limited, 
THE HOCK JOINT. 
Two BONES only concur to form the ginglymus, or true hinge, consti- 
tuting the hock joint: these are the tibia and astragalus. Z’wo articulatory 
surfaces are situated on the sides of the inferior extremity of the tibia, 
presenting two cavities, separated by an eminence, upon which a little 
spot often exists, uncovered by cartilage of encrustation. The astragalus 
presents, on its antero-superior border, two semicircular prominences, 
separated by a deep cavity which exactly corresponds to the inferior tibial 
eminence just mentioned, all being covered by cartilage. 
The tibia and astragalus are united by seven ligaments: two external 
lateral, three internal lateral, one anterior, and a posterior. 
The external lateral ligaments are two, distinguished according to their 
relative position. The superficial external ligament is a large cord, flat- 
tened in its inferior half. It descends from the external tuberosity of the 
tibia, behind the groove which separates this into two parts: taking a 
vertical course, it attaches itself successively to the astragalus, the os 
calcis, os cuboides, the large metatarsal bone, and to the head of the small 
external metatarsal bones. This ligament gives off fibres, anteriorly to 
