118 THE SKELETON OF THE HORSE 
The distal extremity is fused with the tibia, constituting the lateral malleolus. 
Development.—This resembles that of the ulna. The embryonic cartilaginous 
fibula extends the entire length of the leg, but does not articulate with the femur. 
The distal part of the shaft is usually reduced to a fibrous band. Three centers of 
ossification appear, one each for the shaft and the extremities. The distal end 
unites early with the tibia, forming the lateral malleolus. 
It is interesting to note that in some cases the entire shaft of the fibula develops, a reversion 
to the condition in the Miocene ancestors of the horse. 
THE PATELLA 
The patella is a large sesamoid bone which articulates with the trochlea of the 
femur. It presents for description two surfaces, two borders, a base, and an apex. 
The anterior, free surface (Facies libera) is quadrilateral, convex, and rough 
for muscular and ligamentous attachment. 
The articular surface (Facies articularis) is also quadrilateral, but much less 
extensive. It presents a vertical rounded ridge, which corresponds to the groove 
Base 
Later- Medial 
al angle 
angle 
Apex Accessory cartilage Apex 
Fie, 100.—Ricur Parevia or Horse; ANTERIOR VIEW. Itc. 101.—Rreur Parecia or Horse; Postertor Virw. 
1, Attachment area of middle patellar ligament; 1, Medial part, 2, lateral part, of articular surface. 
2, attachment area of lateral patellar ligament and 
biceps femoris. 
on the trochlea of the femur, and separates two concave areas. Of the latter, the 
medial one is much the larger, and is not very well adapted to the corresponding 
ridge of the trochlea; in the fresh state, however, it is completed and rendered more 
congruent by the curved accessory fibro-cartilage. 
The borders, medial and lateral, converge to the apex below, and each forms an 
angle at the base. The medial border is concave. The lateral border is rounded 
and its angle is less prominent. The medial angle and the adjacent part of the 
posterior margin of the base give attachment to the fibro-cartilage of the patella 
(Fibrocartilago patella). 
The base (Basis patellxe) faces upward and backward, and is convex trans- 
versely, concave from before backward. 
The apex (Apex patella) forms a blunt point directed distally. 
Development.— The patella develops as a sesamoid bone from a single center 
in a cartilaginous deposit in the tendon of the quadriceps femoris muscle. 
THE TARSUS 
The tarsus or hock of the horse usually comprises six short bones (Ossa tarsi), 
but exceptionally seven are present. 
