The figure shows that the medullary cavity is traversed for the most
part by fine bony trabeculæ.
]
The =distal extremity= (Extremitas distalis) is large in both directions
and comprises the trochlea in front and two condyles behind. The
=trochlea= consists of two ridges separated by a groove, and forms an
extensive surface (Facies patellaris) for articulation with the patella.
It is very unsymmetrical; the inner ridge or lip is much wider, more
prominent, and extends up higher than the external one, and the two
converge below. The =condyles=, =internal= and =external= (Condylus
medialis, lateralis), are separated by the deep =intercondyloid fossa=
(Fossa intercondyloidea), and articulate with the condyles of the tibia
and the semilunar cartilages of the stifle joint. A ridge connects each
condyle with the lower part of the corresponding lip of the trochlea.
The intercondyloid fossa lodges the spine of the tibia and the crucial
ligaments of the stifle joint, which are attached here.
The condyles are obliquely placed, with their long axes directed
downward, forward, and inward. The articular surface of the external
condyle is more strongly convex from side to side than that of the
inner one, and the ridge which connects it with the trochlea is much
narrower.
The =internal epicondyle= (Epicondylus medialis) is a rounded prominence
on the internal surface of the internal condyle, to which the internal
lateral ligament and the adductor muscle are attached. The corresponding
=external epicondyle= (Epicondylus lateralis) is less distinct; it
presents a mark where the lateral ligament is attached, below and behind
which there is a depression (Fossa musculi poplitei) in which the
popliteus muscle arises. Between the external condyle and trochlea is
the =extensor fossa= (Fossa extensoria), in which the tendon of origin
of the anterior extensor and peroneus tertius is attached.
=Development.=—The shaft and the distal end each ossify from one center,
but the proximal end has two centers, one of which is for the great
trochanter. The edge of the external trochanter also has a separate
center. The proximal end fuses with the shaft at three to three and a
half years, the distal at about three and a half years.
[Illustration:
FIG. 67.—DISTAL EXTREMITY OF RIGHT FEMUR OF HORSE, END VIEW.
]