HOCK JOINT. 381 
one on the astragalus, the other upon the lower and inner surface of the 
os calcis. Zhe internal deep ligament is an extremely thin band ; it is 
attached above to the tibia, just below the attachment of the middle liga- 
ment, and below to the astragalus, nearly at the same point as the superior 
insertion of the middle ligament. 
The anterior ligament is a thin layer, formed of decussating fibres, 
stronger without than within, attached by its superior edge to the tibia, and 
by its inferior edges to the astragalus and to the os cuneiforme parvum. 
The posterior ligament, similar in structure to the anterior, is attached 
to the same bones, behind their articular surfaces. 
The synovial membrane is developed on the internal surfaces of the two 
capsular ligaments, covered also by the “hree internal and the external 
deep ligaments. 
Movements.—This joint allows only of flexion and extension ; but to 
avoid contact between the foot and the tibia in the act of flexion, the 
tibio-astragalan articulation causes the bones below to deviate outwards, 
owing to the obliquity of the articular surfaces. 
ARTICULATIONS BETWEEN THE BONES OF THE TARSUS. 
THE CALCANEO-ASTRAGALAN ARTICULATION, between the bones of the 
first row, is a compound arthrodia, resulting from the coaptation of three 
or four articular surfaces on the posterior face of the astragalus to cor- 
responding facettes on the antero-inferior part of the os calcis. The lateral 
ligaments of the tibio-tarsal articulation are common to this joint; and we 
also have four ligaments proper to it, a superior, external, internal, and an 
interosseous ligament. 
The superior astragalo-calcanean ligament, formed of very short and 
parallel fibres thrown from one bone to the other, is situated near the 
superior extremity of the trochlear astragalan surface, and lined by the 
synovial membrane of the tibio-tarsal articulation. 
The lateral ligaments are two very thin bundles, which unite the os 
calcis to the astragalus laterally, hidden under the ligaments which bind 
the tibia to the tarsus, 
The interosseous ligament is very strong, and occupies a great part of 
the roughened excavations which separate the arthrodial surfaces of the 
os calcis and astragalus. These do not possess proper synovial membranes, 
that is, membranes proper to each, with the exception of one, formed on 
the upper and outer part of this articulation, where a distinct synovial 
membrane exists. The superior arthrodial surface is, however, sometimes 
supplied with synovial membrane, by a prolongation from the tibio- 
tarsal capsule. ‘Two prolongations ascend from the capsule of this articu- 
lation below the inferior arthrodial surfaces of the os calcis and astragalus, 
and thus facilitate a gliding motion, which is very limited. 
THE MOVEMENTS are so limited as to be almost null. 
IN THE ARTICULATIONS OF THE BONES OF THE SECOND ROW among them- 
selves, the cuboid bone joins with the os scaphoides by two arthrodial sur- 
faces, one anterior, the other posterior ; and also with the os cuneiforme 
magnum by two similar surfaces. The os scaphoides articulates with 
the magnum by a vast convex surface; the cuneiforme and magnum 
articulate internally and laterally with the parvum. 
THE LIGAMENTS which keep these diarthrodial surfaces in contact are 
numerous. The astragalo-metatarsal and the posterior tarso-metatarsal 
ligaments are common to this articulation. They consist of— 
Two anterior ligaments, running from the cuboid to the os scaphoides 
