THE POSTERIOR EXTREMITIES. 87 



part which is properly the leg. It is of a long and triangular 

 shape ; connected on the outer side with a mere representa- 

 tive of a bone, which in the horse is not altogether absent, 

 called the fibula {Skel. m) . Of course the tibia has two ends. 

 The top, or upper surface (Skel. I), has two slightly hollow 

 places, divided by a ridge ; upon which hollows the two semi- 

 lunar cartilages of the stifle joint repose. Its bottom, or 

 lower surface {Skel. n), presents three eminences; between 

 which the two projecting parts of one of the bones of the 

 hock exactly fit. The parts thus fitting present rather 

 more than one-third of a circle; and of course admit of 

 extensive motion. The projecting portions on the lower 

 surface, upon the inner and outer parts, present two pro- 

 minences ; which are perfectly natural, though by the igno- 

 rant often mistaken for bone spavin. The most forward 

 part, just above the low^r surface of this bone, lies imme- 

 diately under the skin ; hence it is very liable to be 

 fractured. In situ it will be found placed obliquely back- 

 ward, as the femur is obliquely forward ; forming with that 

 bone an obtuse angle. The superior extremity presents an 

 anterior flat protuberant surface, for receiving the patella. 



The Jibula {Skel. m) appears more designed to keep up 

 that beautiful connexion which we observe throughout ani- 

 mated nature, than for any great use in the machine. It 

 is attached by a synovial surface to the superior part of 

 the tibia ; being placed with its base upwards and its 

 point directed below ; reaching a third of the length of the 

 tibia, to which its lower point is attached. 



The tarsus, or hock {Skel. /), is a most complex and im- 

 portant joint ; and though it consists of several bones, 

 these are so intimately united as to appear a solid mass. 

 The astragalus, or knuckle bone, presents a very irregular 

 figure {Skel. o). Its upper and anterior surface is pulley- 

 like ; having two remarkable partially circular risings, sepa- 

 rated by an intermediate depression ; which risings arti- 

 culate with tlie lower end of the tibia. Posteriorly it has 

 several surfaces of attachment with the calcis {Skel. p) ; 

 receiving the eminences of that bone into considerable de- 

 pressions : and in other places it is closely connected to 

 other bones articulating with the great cuneiform, the 

 cuboid, and others. 



