_1_, Dorsal sacro-iliac ligament; _2_, lateral sacro-iliac ligament;
_3_, sacro-sciatic ligament; _4_, greater sciatic foramen; _5_,
lesser sciatic foramen; _6_, line of attachment of intermuscular
septum between biceps femoris and semitendinosus; _7_, capsule of
hip joint; _8_, rectus parvus or capsularis muscle; _9_, outer
tendon of origin of biceps femoris; _10_, internal, _11_, external,
angle of ilium; _12_, shaft of ilium; _13_, superior ischiatic
spine; _14_, pubis; _15_, tuber ischii; _16_, trochanter major;
_17_, semimembranosus; _18_, fifth lumbar spine; _19_, _20_, first
and second coccygeal vertebræ.
]
The =joint capsule= is roomy. It is attached around the margin of the
acetabulum and the neck of the femur. It is thickest externally.
The attachment on the femur is about 1 cm. from the margin of the
articular surface, except above, where 2 to 3 cm. of the neck is
intracapsular. A thin oblique band corresponding in direction with the
rectus parvus muscle reinforces the antero-external part of the
capsule; this appears to be the feeble homologue of the very strong
ilio-femoral ligament of man. The capsule is very thin under the
ilio-psoas, and is adherent to the muscle. Internally, its fibrous
part is perforated by the pubo-femoral and round ligaments and the
articular vessels.
The =round ligament= (Ligamentum teres) is a strong hand which is
attached in the subpubic groove close to the acetabular notch, passes
outward, and ends in the notch on the head of the femur (Fig. 456).
The =pubo-femoral ligament= (Ligamentum accessorium) does not occur in
the domestic animals other than the equidæ. It is a strong band detached
from the prepubic tendon of the abdominal muscles (Fig. 456). It is
directed outward, backward, and upward, passes through the acetabular
notch above the transverse ligament, and ends behind the round ligament
in the notch on the head of the femur. The origin of the pectineus
muscle is perforated by the ligament, which furnishes attachment to the
greater part of the fibers of the muscle.
[Illustration:
FIG. 155.—LEFT STIFLE JOINT OF HORSE, EXTERNAL VIEW, IN PARTIAL
FLEXION.
The capsules have been removed. _18_, Femur; _20_, patella; _21_,
tibia; _a″_, internal patellar ligament; _b_, external
femoro-patellar ligament; _d_, external semilunar cartilage. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =synovial membrane= is reflected over the intracapsular parts of
these ligaments and covers the fossa acetabuli. A pouch also extends
from the acetabular notch for a variable distance along the subpubic
groove above the pubo-femoral ligament.
=Movements.=—This joint is capable of all the movements of a
ball-and-socket joint, viz., flexion, extension, abduction, adduction,
rotation, and circumduction. The greatest range of movement is displayed
in flexion and extension. When standing at rest, the joint is partially
flexed, the articular angle (in front) being about 100° to 115°. The
other movements occur to a very limited extent in normal action.
Abduction appears to be checked by tension of the round ligament. The
pubo-femoral ligament is tensed most promptly by inward rotation of
the thigh.