DISLOCATIONS OF THE ASTEAGALUS. 125 



Dislocations of the Astragalus alone. Dislocation of the 

 astragalus alone from the malleolar arch as a rule takes place in 

 a forward direction, and generally results from the weight of the 

 body coming upon the upper surface of the astragalus when there 

 is ventro- flexion at the ankle joint, as in alighting upon the toes 

 when jumping from a height. The bone when it is shot forwards 

 as a rule passes somewhat outwards and comes to lie beneath the 

 tendons of the extensor longus digitorum, which together with 

 the skin are tightly stretched over it, and unless the bone is 

 reduced or excised by the surgeon, the integument will slough 

 because it is deprived of its blood supply by the tension to which 

 it is subjected. 



Skull. 



Dislocations at the Temporo-mandibular Joint. The condyle 

 of the mandible may be displaced out of the glenoid fossa of the 

 temporal bone on one or both sides. A hollow will appear in the 

 place where the condyle should naturally be, and the condyle will 

 lie in front of the eminentia articularis. The external pterygoid 

 muscle draws forwards the condyle and with it the meniscus. 

 The temporal, internal pterygoid, and the masseter muscles 

 pull the mandible upwards and constitute the main obstacle to 

 reduction, since they tend to prevent the condyle from passing 

 beneath the eminentia articularis and so back into the glenoid 

 fossa. 



