OSTEOLOGY AND SYNDESMOLOGY. 43 
each are fibrous, and fixed to the head of the tibia by insertions known as 
the oblique ligaments. They serve to deepen the articular surfaces of the 
tibia, and thus to retain the condyles of the femur. They also lessen the 
effect of concussion in the joint and in the limb generally. 
4. SuPERIOR TIBIO-FIBULAR ARTICULATION. But little motion exists 
between the tibia and fibula at their superior extremities: the joint is, how- 
ever, secured by a distinct synovial membrane, sometimes communicating 
with that of the knee joint; there is also a distinct anterior and posterior 
ligament, the former of which is the stronger. 
5. INFERIOR TIBIO-FIBULAR ARTICULATION. Here the inferior extremity 
of the fibula is convex, and received into a depression on the tibia: both 
surfaces are rough superiorly, and covered by cartilage inferiorly: they 
are connected with each other by a strong anterior and posterior ligament. 
The synovial membrane is only a small cul de sac continued from that of the 
ankle joint. Above this is the interosseous ligament, which fastens the 
bones very closely and firmly together. Very little motion occurs in this 
joint beyond a slight yielding of one surface against the other. 
6. ARTICULATION OF THE ANKLE (pl. 126, jigs. 18, 14). This is the 
most perfect ginglymoid or hinge joint in the body, excepting that between 
the ulna and humerus. <A deep mortice-like cavity, with an antero-poste- 
rior edge, is formed by the lower surface of the tibia, and by the two 
malleoli. The fibula forms little more than the outer wall of this cavity. 
In this plays the trochlear surface of the astragalus. The joint is secured 
by very strong lateral ligaments, also by a synovial! membrane and by an 
anterior ligament. 
The internal lateral or deltoid hgament (fig. 14*°) arises from the internal 
malleolus, descends in a radiated manner, and is inserted into the astragalus, 
navicular, and os calcis. 
The external lateral ligaments are three, a posterior, middle, and anterior. 
They all arise from the external malleolus, and are inserted into the astra- 
galus or os calcis (fig. 14%"). 
The anterior or tvbio-tarsal ligament arises from the anterior edge of the 
tibia and tibio-peroneal ligament, and is inserted into the upper and outer 
part of the astragalus. 
7. ARTICULATION OF THE BoNES OF THE Tarsus. The seven bones of 
the tarsus are connected in such a firm and close manner as to admit of little 
motion between any two except at the articulation between the astragalus 
and the scaphoid. 
_ The astragalus is connected with the os calcis by a strong interosseous 
ligament. ‘There are also two synovial membranes. The head of the 
astragalus fits into the glenoid surface of the scaphoid, in which it enjoys 
considerable motion. The synovial membrane in the joint is covered 
superiorly by the superior astragalo-scaphoid ligament. Below is the 
inferior calceo-scaphoid ligament (fig. 16*) extending from the anterior 
inferior part of the os calcis to the lower surface of the scaphoid. There 
is another strong ligament in this joint, called the superior calceo-scaphoid. 
The inferior and superior calceo-cuboid ligaments (fig. 167), as their name 
749 
