OSTEOLOGY AND ARTHROLOGY ?>7 



inferior extremity, a small prominence, which replaces the 

 fibular malleolus. The ruminants must, however, be ex- 

 cepted, in which we find in this region a special bone, which 

 certain authors look on as the inferior part of the fibula 

 (see p. 97). The inferior surface of this extremity of the 

 tibia is articular ; and is in contact with one of the tarsal 

 bones, the astragalus. Because the superior surface of 

 this latter has the form of a pulley, a pulley much more 

 marked than that on the human astragalus, the correspond- 

 ing surface of the tibia, which has the opposite form, 

 presents two lateral cavities, separated by a median ridge, 

 which is directed forwards and slightly outwards ; this 

 ridge projects into the groove of the pulley. 



The Fibula. — This bone, situated at the back of the 

 external surface of the tibia, is, as we have said, more or 

 less developed. Its superior extremity, or head, articu- 

 lates with the external tuberosity of the tibia. Its inferior 

 extremity, when it exists — it is this which disappears in 

 animals which have the fibula incompletely developed — 

 forms a prominence which, placed on the external surface 

 of the inferior extremity of the tibia, articulates with the 

 astragalus, and recalls the external malleolus of man. 



We have stated above that it is the inferior extremity 

 of the fibula which disappears when the bone is incom- 

 pletely developed ; it is necessary to except the bat, in 

 which the fibula, fairly well developed at its inferior 

 extremity, by which it articulates with the tibia, thins 

 off in its superior portion, and does not reach the corre- 

 sponding extremity of the latter. Further, as in this 

 animal the surface of the knee, which corresponds to the 

 anterior surface of the same region in other animals, is 

 turned backwards, the result is that the fibula is situated 

 on the inner side of the tibia, instead of being placed on 

 the outer. 



The Foot 



The foot, in animals, as well as in man, is formed of three 

 portions, which, as we pass from the part which articulates 

 with the leg towards the terminal extremity, are: the tarsus, 



