These figures show the internal architecture of these bones, and
especially the great extent of the medullary cavity as compared with
those of the horse (Figs. 67 and 72).
]
The =femur= has a relatively small shaft, which is cylindrical in its
middle, prismatic below. The trochanter minor has the form of a rough
tuberosity, and is situated higher up than in the horse and encroaches
on the posterior surface. The trochanteric ridge (Crista
intertrochanterica posterior) connects it with the trochanter major. The
third trochanter is absent. The supracondyloid (plantar) fossa is
shallow. The proximal extremity is very wide. The head is smaller than
in the horse and the articular surface extends considerably on the upper
surface of the neck. Instead of the notch there is a small depression on
the middle of the head for the attachment of the round ligament. The
neck is well defined except above. The trochanter major is very massive
and is undivided; its external surface is very rough. The trochanteric
fossa is deep, but does not extend so far downward as in the horse. The
distal end presents no very striking differential features, but the lips
of the trochlea are less oblique than in the horse, and converge very
slightly below. The proximal extremity unites with the shaft at about
three and one-half years, the distal at three and one-half to four
years.
The =tibia= resembles that of the horse rather closely, but is somewhat
shorter. The shaft is distinctly curved, so that the inner side is
convex. The posterior surface is not divided into two areas, and the
lineæ musculares are fewer and extend up higher than in the horse. The
articular grooves and ridge of the distal end are almost sagittal in
direction, and present an extensive but shallow synovial fossa. The
external groove is separated by a sharp ridge from an outer area which
is for articulation with the external malleolus. The anterior part of
the internal malleolus is prolonged downward and has a pointed end. The
groove behind it is broad and well defined. Externally there is a deep
narrow groove which separates two prominences. The proximal extremity
fuses with the shaft at three and one-half to four years, the distal at
two to two and one-half years.
The =fibula= usually consists of the two extremities only. The head is
fused with the external condyle of the tibia and bears a small
blunt-pointed prolongation below. The distal end remains separate and
forms the external malleolus (sometimes called the os malleolare). It is
quadrilateral in outline and compressed from side to side. The proximal
surface articulates with the distal end of the tibia, and bears a small
spine which fits into the groove on that bone. The distal surface rests
on the fibular tarsal, and the inner articulates with the external ridge
of the tibial tarsal bone. The outer surface is rough and irregular.
The early cartilaginous fibula is complete, but later the shaft is
reduced and is usually represented by a fibrous cord which connects the
two ends. In some cases, however, the upper part undergoes partial
ossification, forming a slender rod which is usually united with the
outer border of the tibia and is joined to the head by fibrous tissue.
The =patella= is long, narrow, and very thick. The anterior surface is
strongly convex and very rough and irregular. The articular surface is
convex from side to side and nearly straight in the vertical direction.
The large prominence on the inner side for the attachment of the
accessory cartilage allows prompt determination of the side to which the
bone belongs. The apex is more pointed than in the horse.
The =tarsus= consists of five pieces; the central and fourth, and the
second and third tarsal bones are fused.
The =tibial tarsal= bone is relatively long and narrow, and is somewhat
flattened from before backward. It bears a trochlea at either end. The
groove and ridges of the proximal trochlea are not spiral, but almost
sagittal; the outer ridge is the wider, and articulates with both tibia
and fibula. The distal trochlea consists of two condyles divided by a
groove, and articulates with the combined central and fourth tarsals.
The posterior surface bears a large oval facet for articulation with the
fibular tarsal; this occupies most of the surface, and is convex and
grooved from above downward. The outer surface presents two facets for
articulation with the fibular tarsal, and is excavated and rough
elsewhere. The inner surface bears a tuberosity at its upper part, and
is flattened below.
The =fibular tarsal= bone is longer and more slender than in the horse.
The distal part of the body is compressed laterally, and bears a
projection in front which articulates with the external malleolus. The
tuber calcis is marked posteriorly by a wide shallow groove, which is
coated with cartilage in the fresh state.
The =central= and =fourth tarsals= are fused to form a large bone (Os
centrotarsale quartum, scapho-cuboid), which extends across the entire
width of the tarsus and articulates with all of the other bones. The
greater part of the upper surface is molded on the distal trochlea of
the tibial tarsal, and its inner part rises high above the rest
posteriorly. Externally there is a narrow undulating surface for
articulation with the distal end of the fibular tarsal bone. The
posterior surface bears two tuberosities, of which the outer one is
rounded, the inner more prominent and narrower.
The =first tarsal= bone is quadrilateral and small. It articulates with
the central above, the metatarsus below, and the second tarsal in front.
The =second= and =third tarsals= are fused to form a rhomboid piece. The
proximal surface is concavo-convex, and articulates with the central
component. The distal surface is undulating and rests on the metatarsus.
The external surface bears a small facet in front for the fourth tarsal
component, and the posterior surface a very small one for the first
tarsal bone.
The =large metatarsal= bone is about one-seventh (ca. 3 cm.) longer than
the corresponding metacarpal. Its shaft is compressed laterally and is
distinctly four-sided. The groove on the anterior surface is deep and
wide. The posterior surface is marked by variable grooves. The upper
foramen on this surface does not perforate the shaft, but passes
obliquely through the extremity, opening on the posterior part of its
proximal surface. The postero-internal angle of the proximal end bears a
facet for articulation with the small metatarsal bone.
[Illustration:
FIG. 104.—SKELETON OF DISTAL PART OF LEFT HIND LIMB OF OX, INTERNAL
VIEW. _24_, Tuber calcis; _25_, large metatarsal bone; _30_, first
phalanx; _31_, second phalanx; _32_, third phalanx. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =small metatarsal= bone is a quadrilateral disc a little less than
an inch in width and height. Its anterior face bears a facet for
articulation with the large metatarsal bone.
The large metatarsal bone is usually regarded as consisting of the
fused third and fourth metatarsal bones. The medullary cavity is
subdivided like that of the large metacarpal bone. Some anatomists,
however, consider that the ridges at the upper end of each border
represent the second and fifth metatarsals (Rosenberg and Retterer).
On this basis the small bone would be the first metatarsal.
The =phalanges= and =sesamoids= resemble those of the thoracic limb so
closely as to render separate description unnecessary.