16 VETERINARY STUDIES 



internal tuberosity. Its articular surface consists of two shallow 

 cavities and a median ridge, all three of which extend diagonally 

 forward and backward. 



This bone articulates with four others ; viz. femur, fibula, and 

 one of the tarsal bones, the astragalus. 



The fibjila is a small rudimentary bone which articulates with 

 the external portion of the head of the tibia, and is situated on 

 the external side of that bone. 



The patella is small, short, and located in front of the lower 

 extremity of the femur, and attached to the tibia below by three 

 strong ligaments. It is often displaced outward when the limb 

 is in the condition popularly known as "stifled." This bone 

 offers for study three faces: superior, to which muscles are 

 attached; the anterior, which is convex and somewhat irregu- 

 lar; and the posterior, which is so shaped as to fit nicely into 

 the femoral groove already mentioned. 



Foot. — In its anatomy, the foot bears a very close resemblance 

 to the corresponding portion of the anterior limb, and is divided 

 for study into the tarsus, metatarsus, and digit. 



The tarsus is composed of six or seven small bones, arranged 

 in two rows, forming a very complicated articulation at the 

 hock. The upper row contains the astragalus and os calcis. The 

 lower row usually consists of four small bones. Two of these 

 are especially interesting because they are the common seat of 

 bone spavin, a serious cause of lameness and unsoundness. 



The astragalus is interesting because it furnishes the articu- 

 lar surfaces for the lower end of the tibia. Note the peculiar, 

 diagonal, pulley-like groove with which the astragalus articu- 

 lates with the tibia and its important bearing in the action of the 

 hock and cannon. 



The os calcis is somewhat elongated and lies behind the 

 astragalus. It corresponds to the prominent portion of the 

 human heel and is the seat of the "capped hock." The bones 

 of this region correspond to the human tarsal bones making up 

 the ankle. 



The metatarsals closely resemble the metacarpals of the front 

 leg and consist of three bones, a large one in the center and 

 one small rudimentary bone on each side, i.e. on the inside and 

 outside of the middle bone. The large metatarsal furnishes the 

 supporting axis for this region as in the anterior limb. The 

 shaft is fairly smooth and has a small articular surface on each 



