DR. J. MURIE ON THE ANATOMY OF THE SEA-LION, 585 
circular than the inner one, the latter being more elongated from before backwards. 
They are only moderately thick at the edges, and, as a whole, are comparatively flat 
and discoid. ‘The popliteus muscle is firmly adherent by tendon to the posterior border 
of the outer one. 
Peroneo-tibial articulations.—TVhere is very little interosseous membrane or ligament 
present. A thin band, less than an inch broad, is found near the middle of the shafts 
of the tibia and fibula (7’, fig. 40); and a narrower, but thicker and stronger, fasciculus 
exists fully an inch below this (7°). Both are oblique in direction, the tibial end being 
highest. ‘The paucity of interosseous ligamentous substance of the lower leg admits of 
moderately easy movements of the bones towards each other, though this is less than 
in the forearm. 
A strong set of aponeurotic fibres firmly unites the inferior extremities of the tibia 
and fibula together; these are oblique in direction above, and transverse below, and 
doubtless represent the anterior inferior, the posterior inferior, and the transverse 
ligaments of the tibio-peroneal articulations (7.t.p, figs. 40 & 41). These allow of a 
very limited gliding movement between the lower articular surfaces of the tibia and 
fibula. 
Anklejoint.—The most remarkable feature in this joint, as will further be referred 
to, is the oblique position and manner of flexion of the articulating bones. Notwith- 
standing their anomalous position and movement, the ligaments binding the bones are 
normal in number and attachments, although their precise relative dispositions to each 
other are somewhat changed. 
The anterior ligament (a, fig. 40) is of moderate thickness. It extends across from 
the tibial to the fibular malleolus, and stretches from this downwards to the astragalus, 
in front of its articulating surface. The anterior ligament is considerably strengthened 
by a strong accessory ligamentous tendon (acc), which crosses obliquely in front of the 
ankle from within outwards, and, as it passes round the outer articular prominence of 
the astragalus, spreads out, and is inserted partly into the anterior portions of the 
astragalus and os calcis. 
Internal lateral ligament (i.1, figs. 39 & 41).—This is a very strong, thick band of 
tendon, which is attached superiorly to the tip of the internal malleolus, and from this 
stretches backwards and downwards to the inner surface of the hinder prominence of 
the astragalus, but not reaching the os calcis or the scaphoid. It is not of a deltoid 
form as in Man and the Higher Primates, but is a straight, uniformly powerful band 
half an inch broad. 
Action. When the foot is thrown forwards and inwards, as occurs in this animal’s 
mode of walking, at such times the internal ligament is tense. Again, when the foot is 
thrust backwards and pronated, as in swimming, the ligament is still kept moderately 
on the stretch. In all other movements it is in a state of relaxation. 
External lateral ligament.—The three fasciculi or slips of which this ligament is 
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