ASTRAGALUS. 93 



FIBULA. 

 (PL. L ?/.) 



This is a long slender bone, little developed in the horse, and 

 is an appendage to the tibia, being attached to the outer side 

 of that bone, and extending from its head to its lower third, to 

 which it is affixed by a ligament ; the space between the two 

 bones is called the tibial arch. 



The head, or superior iKtrt, is nodular, somewhat ' flattened, 

 and roughened externally for the attachment of the external 

 lateral ligament of the joint above ; internally it articulates with 

 the external lateral part of the head of the tibia. Distally the 

 bone becomes slender, and tapers to a point, from which a liga- 

 ment is sometimes continued the whole length of the tibia. The 

 peroneus muscle arises chiefly from the fibula. 



TARSUS. 



The tarsus, or hock, corresponding to the ankle-joint of a man, 

 is composed of six irregular, compact bones, placed between the 

 distal end of the tibia and the proximal end of the metatarsus ; 

 they are arranged in two series ; one, consisting of the cuboid 

 and three cuneiform bones, the magnum, medium, and parvum, 

 corresponds to the lower row of carpal bones ; the other, or upper 

 series, consists of the astragalus and calcaneum, the first, forming 

 with the bone above the mobile portion of the joint, may be said 

 to correspond to the upper row of carpal bones, while the latter, 

 being the lever bone, corresponds to the trapezium. These 

 bones, like those of the carpus, are thickly covered on their 

 articular surfaces by cartilage, which acts as a protection against 

 concussion. 



ASTRAGALUS. 

 (Fig. 22. 2.) 



This, otherwise termed the os tali or ankle bone, is a pulley- 

 like bone, placed immediately below the' tibia, with which it 

 articulates. A very large proportion of the surface of this bone 

 is articular. 



The superior or supero-anterior surface presents an articular 



