254 



THE EXTERIOR OF THE HORSE. 



calcaneus and the astragalus, the three pieces of the metatarsus, and play the 

 role of dispersing agents for the weight of the body in movement. 



Ligaments. The bones of which we have spoken are joined in a most 

 intimate manner to the adjoining structures, the tibia and the metatarsus, by 

 capsular and funicular ligaments, which allow perfect freedom in the tibio-tarsal 

 hinge. 



Among these ligaments, two lateral, external and internal, unite the external 

 and the internal tuberosities of the tibia to the head of the corresponding rudi- 

 mentary metatarsal bones. They are elongated, rounded, unelastic, tortuous 

 according to their length, and take successive attachments on the lateral surfaces 

 of the bones which lie in their course. 



Two capsular ligaments of unequal resistance protect the tarsus in front and 

 behind. The anterior, somewhat thin and stronger outwardly, extends from the 

 anterior edge of the inferior articular surface of the tibia to the surface of the 

 tarsal bones and the canon. It protects the synovial membrane in front. The 

 posterior affects a general analogous disposition as to its attachments, but it is 

 thin and membranous in its superior part in order to yield easily to movements 

 of flexion, whilst in its centre and inferiorly it is reinforced by a plate of fibro- 

 cartilage, which serves as a gliding surface for the tendon of the deep flexor of 

 the phalanges. It keeps in position the articular synovial membrane behind. 



Articular Synovial Membranes. Of the five tarsal articulations, only 

 one is interesting from an external point of view. This is the tibio-astragaloid, 

 which is lined by a special synovial membrane. Although this membrane is 

 firmly maintained on the sides by the lateral ligaments, and in front and behind 

 by the capsular ligaments described above, nevertheless, it presents certain weak 

 spots which may possibly yield under the influence of the interarticular pressure 

 from an excess of synovial secretion. These spots are three in number : the one 



antero-internal, where the ligament is not protected 

 by the anterior tibial muscles, the other two poste- 

 rior, and situated above the reinforcing fibro-carti- 

 lage of the posterior ligament. Pressure applied to 

 any one of these swellings will cause the liquid to 

 flow into the others, a fact which demonstrates con- 

 clusively enough their intercommunication. 



Tendons and Tendinous Bursse. The ten- 

 dons of the various muscles glide over the bones 

 and the ligaments of the hock by means of synovial 

 bursse, of which it is necessary to say a few words. 



In front and on the outside, the anterior capsu- 

 lar ligament is maintained by the tendons of the 

 anterior extensor of the phalanges and the flexor of 

 the metatarsus, which is held by a fibrous aponeu- 

 rosis in the bend of the hock ; their movements are 

 effected through the intervention of the underlying 

 connective tissue. 



On the outside is the tendon of the lateral ex- 

 tensor of the phalanges, which a bursa of its own 

 enables to glide through a duplicate of the external lateral ligament. 



On the inside we find the tendon of the oblique flexor of the phalanges (Fig. 



FIG. 76. 



