_Ligaments of the Pelvis._--The ilium and sacrum are articulated at the
auricular facet of the ilium and the corresponding rough surface of the
sacrum. The joint is an amphiarthrosis, permitting very little movement.
A =capsular ligament= surrounds the articular surface, being attached to
the bones about its circumference; it is short and strong. Craniad of
the capsule is a thick very short ligament, composed of very strong
transverse fibres passing from the rough surface of the sacrum to the
corresponding rough surface of the ilium. This forms the =lateral
iliosacral ligament=, which is united at its caudal border to the
capsule.
A strong, wide ligamentous band passes from the dorsal border of the
ilium to the sides of the sacrum. This is indistinctly subdivided into
several bands, which together represent the =long= and =short posterior
iliosacral ligaments= of man.
_Symphysis pelvis._--The medial borders of the pubis and ilium meet in
the middle line ventrad of the pelvis and are here united by cartilage.
The joint is strengthened by numerous small bands which pass across the
line of junction from one side to the other; these occur on both
surfaces.
_The Hip-joint._--The hip-joint is an =enarthrosis=, or ball-and-socket
joint in which more than half the spherical head of the femur is
received into the acetabulum. The depth of the acetabulum is increased
by a rim of fibrocartilage about its margin, forming the =labrum
glenoidale=. This passes across the acetabular notch, forming the
=transverse ligament= of the acetabulum; beneath it blood-vessels and
nerves pass into the acetabular cavity.
The =capsule of the joint= is large and loose. It is attached about the
margin of the acetabulum, and passes over the head of the femur, to be
attached to the bone several millimeters distad of the head. It thus
encloses both the head and the neck of the femur.
The =ligamentum teres=, or round ligament, is a very strong, short
ligament which passes from the depression in the head of the femur to
the bottom of the acetabulum.
=The Knee-joint= (Figs. 60 and 61).--The joint between the femur and the
tibia is very complex. The surfaces of the condyles of the femur do not
correspond to those of the condyles of the tibia. Between the ends of
the two bones are placed two disks of cartilage, the =menisci=, or
semilunar cartilages (Fig. 60, _c_ and _d_; Fig. 61, _a_ and _b_), of
such a form that the congruity of articular surfaces is restored. Each
meniscus has a proximal surface corresponding to the form of one of the
condyles of the femur, and a distal surface corresponding to a condyle
of the tibia. The menisci are held in position by ligaments. The
knee-joint permits not only backward and forward movement, but also a
small amount of rotary motion.
The joint has two =capsules=, one on the dorsal (convex) side, the other
on the ventral side. The two communicate only by a small passageway
lying within the joint between the ends of the bones. The dorsal one is
attached to the femur several millimeters proximad of the patellar
surface and some distance on each side of the latter. The patella is
imbedded in its outer wall, and it is attached to the tibia on the edges
of the articular surface of the latter, from the crest to the
tuberosities. The capsule is also attached laterally and medially to
the sides of the menisci, and is closely united to the patellar
ligaments. Its cavity contains a mass of yellow fat.
The ventral capsule is attached to the borders of the articular surfaces
of the femur and tibia on their ventral sides, to the menisci, and to
the epicondyles of the femur and the tuberosities of the tibia. Its
walls are stronger and its cavity smaller than those of the dorsal
capsule.
The ligaments of the knee-joint (Figs. 60 and 61), aside from the
capsules, may be classified into: (1) those which are connected with the
patella; (2) =collateral= ligaments (Fig. 60, _i_ and _j_), which pass
from the epicondyles directly distad along the sides of the joint to the
tibia or fibula; (3) =crucial= ligaments (Fig. 60, _g_ and _h_; Fig. 61,
_c_ and _d_), which cross within the joint from one side of the femur to
the opposite side of the tibia; (4) ligaments which hold the menisci in
place (Fig. 60, _e_ and _f_; Fig. 61, _e_ and _f_).
(1) LIGAMENTS OF THE PATELLA.--The patella is imbedded in the dorsal
wall of the dorsal capsule of the joint. From its distal end a strong
tendon or ligament passes distad to the crest of the tibia. This is
known as the =ligamentum patellæ=: it may be considered a part of the
tendon of M. quadriceps femoris. On the lateral side the capsule of the
joint is strengthened by the transverse fibres of the tendon of M.
plantaris, which aid in holding the patella in place.
(2) COLLATERAL LIGAMENTS.--Of these there are two. The =ligamentum
collaterale fibulare= (Fig. 60, _j_) is attached to the lateral
epicondyle of the femur and passes distad across the tendon of the
plantaris muscle to the head of the fibula. Dorsad of the fibular
ligament and parallel with it passes the tendon of origin of the
extensor longus digitorum. The =ligamentum collaterale tibiale= (Fig.
60, _i_; Fig. 61, _g_) begins on the medial epicondyle of the femur and
passes distad to the lateral tuberosity of the tibia; part of it passes
one to one and a half centimeters distad of the tuberosity to be
attached to a rough ridge on the side of the tibia.
[Illustration: FIG. 60.--KNEE-JOINT, FROM THE DORSAL OR PATELLAR SIDE.