_21_, Tibia; _22_, trochlea of tibial tarsal bone; _25_, large
metatarsal bone; _50_, dorsal or oblique ligament. (After
Ellenberger-Baum, Anat. für Künstler.)
]
There are four =synovial sacs=: 1. The =tibio-tarsal sac= lubricates the
proximal joint, and is much the largest and most important. It is
chiefly involved in the swelling produced by excess of fluid in the
joint cavity, when the capsule bulges antero-internally and
postero-superiorly. 2. The =first intertarsal sac= lines the joints
formed by the tibial and fibular tarsal bones above, and the central and
fourth tarsals below; it communicates in front with the proximal
synovial capsule. 3. The =second intertarsal sac= lubricates the joints
formed between the central tarsal and the bones below and on either
side. 4. The =tarso-metatarsal sac= lubricates the joints formed between
the tarsal and metatarsal bones, those between the proximal ends of the
metatarsal bones, and those formed by the third tarsal with the bones on
either side.
=Common Ligaments.=—The =external lateral ligament= (Ligamentum
collaterale fibulare longum et breve) consists of two distinct bands
which cross each other. The =long= (superficial) =ligament= arises on
the posterior part of the external malleolus, is directed almost
straight downward, and is attached to the fibular and fourth tarsal
bones and the large and external small metatarsal bones. It forms a
canal for the lateral extensor tendon. The =short= (deep) =ligament=
arises on the anterior part of the external malleolus, is directed
chiefly backward, and ends on the rough excavation on the external
surface of the tibial tarsal and the adjacent surface of the fibular
tarsal bone.
[Illustration: