THE FIBULA Maly 
patellar ligaments. A semicircular smooth notch, the sulcus muscularis, separates 
the tuberosity from the lateral condyle, and gives passage to the common tendon 
of origin of the extensor digitalis longus and the peroneus tertius. 
The distal extremity (Extremitas distalis) is much smaller than the proximal 
one; it is quadrangular in form and larger medially than laterally. It presents an 
articular surface (Cochlea tibixe), which is adapted to the trochlea of the tibial 
tarsal bone, and consists of two grooves separated by a ridge. The ridge and 
grooves are directed obliquely forward and laterally, and are bounded on either 
side by the malleoli, to which the collateral ligaments of the hock joint are at- 
tached. A shallow synovial fossa is usually present on the middle of the articular 
ridge. The lateral groove is wider and shallower than the medial one; it is fre- 
quently marked by a line or groove which indicates the former demarcation between 
the tibia and fibula. The medial malleolus (Malleolus medialis) is the more prom- 
inent of the two, and forms the anterior boundary of a groove for the tendon of the 
flexor digitalis longus. The lateral malleolus (Malleolus lateralis) is broader, and 
is marked by a vertical groove for the passage of the lateral extensor tendon. 
Development.—The tibia has the usual three chief centers of ossification and 
supplementary ones for the tuberosity and the lateral malleolus. The latter is 
really the distal end of the fibula; it is a separate piece at birth, and the line of 
union is commonly quite evident in the adult in the articular groove. The proxi- 
mal end unites with the shaft at about three and a half years, and the distal end at 
about two years of age. 
Fic. 98.—Proxmmat Extremity oF Ricut Trsia oF Fic. 99.—Distat Extremity oF Ricur TIiBra (AND 
Horse; Enp View. 
1, Medial condyle; 2, lateral condyle; 3, groove 
on 2 for popliteus tendon; 4, popliteal notch; 5, tuber- 
osity; 6, groove for middle patellar ligament; 7, tuber- 
cles of spine; 8, sulcus muscularis; /.c.a., l.c.p., depres- 
sions for attachment of anterior and posterior cruciate 
ligaments; /, m, m, depressions for attachment of 
menisci. 
Frsvuta) or Horse; Env View. 
1, 1’, Articular grooves; 2, intermediate ridge and 
synovial fossa; 3, line of fusion of primitive distal end 
of fibula with tibia; 4, medial malleolus; 5, 5’, lateral 
malleolus; 6, anterior border. 
THE FIBULA 
The fibula of the horse is a much reduced long bone, situated along the lateral 
border of the tibia. 
The shaft (Corpus fibulze) is a slender rod which forms the lateral boundary of 
the interosseous space of the leg; it usually terminates below in a pointed end about 
one-half to two-thirds of the way down the lateral border of the tibia. 
The proximal extremity or head (Capitulum fibule) is relatively large, and is 
flattened transversely. Its medial surface presents a narrow area (Facies articu- 
laris capituli) along the upper border for articulation with the lateral condyle of 
tibia. The lateral surface is rough and gives attachment to the lateral ligament 
of the stifle joint. It has rounded anterior and posterior borders. 
