6o THE SURGICAL ANATOMY OF THE HORSE 



THE TIBIA 



The tibia is placed obliquely in the limb, running downwards and 

 backwards from the stifle joint above to the hock joint below. It belongs 

 to the class of long bones, and consequently possesses a shaft and two 

 extremities. 



The shaft presents for description three surfaces which are named 

 respectively, posterior, external and internal. The external surface, in its 

 upper third, looks outwards, and the upper portion of the surface is 

 widest and is slightly depressed. In its middle third, the surface becomes 

 slightly convex, whilst its lower third, which looks directly forwards, is 

 almost flat. It will thus be seen that the external surface takes a 

 somewhat spiral direction. This surface is clothed by the muscular or 

 deep division of the flexor metatarsi. 



The inner surface of the shaft is also widest superiorly, and it tapers 

 gradually as we descend. This surface is slightly convex. Superiorly 

 it is roughened for the attachment of muscles, but for the rest of its 

 extent it is smooth and is immediately subcutaneous. It corresponds 

 to the human "shin." 



The posterior surface may be divided into three areas. The 

 uppermost is triangular in outline, the apex of the triangle being 

 directed downwards and inwards. This area is concave and smooth, and 

 it accommodates the popliteus muscle. The central area is also 

 triangular, but in this case the apex is directed upwards and outwards. 

 It presents a number of parallel ridges which are roughened and from 

 which the fibres of the flexor perforans muscle arise. 



On the line of division of the two areas just described, and slightly to 

 the outer side of the middle line of the back of the bone is the nutrient 

 foramen, the direction taken by the canal into which the foramen opens 

 being obliquely downwards and inwards. 



The most inferior of the three areas is flattened and somewhat 



