POSTERIOR MEMBER. 255 



76) having almost the same disposition along the internal lateral ligament, while 

 below, supplied also with a special synovial bursa, the cunean tendon of the 

 flexor metatarsi passes obliquely backward over the internal face of the hock ; 

 this, when in a state of abnormal distention, is capable, according to Bouley,* of 

 simulating a spavin by the enlargement that it forms under the skin at the very 

 point where a spavin is located. 



Finally, at the back, the tarsus is transformed into a fibrous envelope known 

 as the tarsal sheath. Its anterior wall is constituted by the posterior ligaments 

 of the hock ; it is completed behind by an arch of fibrous tissue extending from the 

 posterior border of the calcaneus to the inner side of the tarsal bones. It gives 

 passage to the perforans tendon through the medium of a synovial membrane. 

 The latter extends from the inferior fourth of the tibia downward to about the 

 superior third of the canon. When this synovial membrane becomes dilated it 

 forms two hernige superiorly in the hollow of the hock, one on the outer and the 

 other on the inner side, posterior to the corresponding culs-de-sac of the tibio- 

 astragaloid articulation. It is also prolonged downward along the flexor tendons 

 in the shape of a tumor of variable size, sometimes simulating curb. 



The summit of the calcaneus also presents a little synovial gland, where the 

 tendon of the gastrocnemius muscle is attached, to facilitate its gliding upon the 

 aforesaid bones during extension and flexion of the metatarsus. This bursa, 

 being very firmly sustained over its periphery, is not liable to become distended 

 and form external dilatations. It is different, however, with the bursa which 

 facilitates the play of the superficial flexor of the phalanges over the summit and 

 along the posterior border of the calcaneus, and which almost entirely covers this 

 surface. This tendon, after winding around that of the gastrocnemius, widens, 

 becomes inflected over the head of the calcaneus, almost completely enveloping 

 it, and is then continued in the region of the canon. Now, it is for a distance of 

 about five centimetres along the perforatus tendon in front of the summit of the 

 calcaneus that the enlargement manifests itself when, from excessive secretion 

 of the synovial fluid, this membrane becomes distended. 



External Conformation.— The hock is a centre of movement, 

 whose perfect integrity is so important, as affecting the usefulness of 

 the animal, that the eye should know and recognize its normal form 

 in its least details. 



This region is divided into four faces : an anterior, a posterior, and two 

 lateral. 



a. Anterior Face. — The anterior face (Fig. 77, A) corresponds to the 

 summit of the tibio-tarsal angle; it has received the name oi fold of the hock, 

 and shows, on each side, the profile of the lateral faces. It presents, outwardly, 

 above and behind, the summit, a, of the calcaneus ; below this, the external 

 tuberosity of the tibia, b ; finally, below, the eminence, e, formed by the base 

 of the calcaneus, the cuboid and the head of the external rudimentary metatarsal 

 bone. On the inside, it offers the very prominent internal tuberosity of the 

 tibia, d ; lower down, the internal tubercle of the astragalus, e ; finally, altogether 

 below, the prominence of the head of the internal metacarpal bone,// in its 



1 H. Bouley, Nouveau Dictionnaire pratique, etc., t. x. p. 569. 



