. THE TIBIO-FIBULAR JOINTS. ' 295 
Equally strong but much shorter bands are found on the superior and inferior 
aspects of the joint, The former is intimately associated with the tendon of the 
biceps which strengthens the upper aspect of the joint and here also is found the 
occasional opening by which it communicates with the knee-joint. 
The synovial membrane is in certain cases continuous with that of the knee- 
joint in the manner already described. 
The interosseous membrane (membrana interossea cruris, Figs. 224, and 226) 
plays the part of an accessory ligament both for the upper and the lower tibio-fibular 
joint. It is attached to the interosseous borders on the shafts of the tibia and 
fibula, and binds them together. The general direction of its fibres is from the 
tibia downwards and outwards to the fibula, but many fibres pass in the opposite 
direction. The membrane may extend upwards until it comes into contact with 
the ligaments of the superior tibio-fibular joint, but there is always a vertical oval 
aperture in its ee part for the forward passage of the anterior tibial vessels. 
This aperture (Fig. 224), which is about one inch long, adjoins the shaft of the 
fibula at a point “rather less than one inch below its head. Towards the lower 
end of the leg the distance between the tibia and the fibula rapidly diminishes, and 
consequently the width of the interosseous membrane is correspondingly reduced, 
so that it is tense throughout its entire length, In the lower part of the membrane 
there is a small opening for the passage of the anterior perforating vessels. There 
is no sharply-marked demarcation between the interosseous membrane and the 
' interosseous ligament which connects the lower ends of the tibia and fibula—the 
one, indeed, may be said to run into the other. 
The inferior tibio-fibular joint (syndesmosis tibio-fibulare) is not on all 
occasions provided with articular cartilage, so that it may either be a separate articu- 
lation, or it may merely present a series of hgaments which are accessory to the ankle- 
joint, because it is clear that, under any circumstances, the object aimed at in this 
articulation is to obtain additional security for the ankle-joint. The articular surface 
on the tibia, when present, constitutes a narrow articular strip on the outer side of the 
lower end of the bone, and the joint-cavity is practically an upward extension of the 
ankle-joint. The corresponding fibular facet 
is continuous with the extensive articular 
area, by means of which the fibula articulates 
with the astragalus. By far the greater part 
_ of the opposing surfaces of tibia and fibula 
are, however, non-articular and rough. 
The supporting ligaments are of great 
strength. 
The anterior inferior tibio-fibular ligament 
Interosseous 
membrane 
Posterior 
inferior tibio- 
fibular ligament 
(ig. malleoli lateralis anterius, Fig. 229) 
- consists of strong fibres which pass obliquely 2-2 Transverse 
_ downwards and outwards from the front of =| 2 a ome 
the lower end of the tibia to the front of 2] 2 Internal lateral 
_ the external malleolus. 2\3 Cea 
; The posterior inferior tibio-fibular liga- z eg ankle-joint 
_ ment (lig. malleoli lateralis posterius, Figs. =)” 
226 and 227) is equally strong, and passes £] z 
in a similar direction between corresponding 2| 52 
- posterior surfaces. ae Nei ibed 
A transverse inferior tibio-fibular liga- i of aspeaioid 
ment (Figs. 226 and 227) stretches, in the 
direction indicated by its name, between the F1¢. 226.—Posrrrror Aspect or INFERIOR 
posterior inferior border of the tibia and Te pam acl ai 
the upper end of the pit on the inner and posterior aspect of the external malleolus. 
An interosseous ligament (Fig. 227), powerful and somewhat extensive, connects 
the contiguous rough non-articular surfaces. Superiorly, as already mentioned, it 
is continuous with the interosseous membrane. Anteriorly and posteriorly it 
comes into contact with the more superficial ligaments. Inferiorly it descends until 
it comes into intimate association with the joint-cavity. 
