972 THE OSTEOLOGY AND MYOLOGY OF THE DEATH ADDER, 



prefrontal moves upwards and outwards, the lower portion coming 

 also forward. This lower border rests on the superior surface of 

 the maxilla which is, however, only slightly concave. Usually 

 in venomous snakes there is a well marked ball and socket joint 

 developed between these two bones, and accordingly considerable 

 motion is possible ; but in the case of Acanthoj^his the greatest 

 movement takes place between the frontal and prefrontal. This 

 probably misled Krefft when he described the fangs as being per- 

 manently erect. The transpalatine articulates with the posterior 

 extremity of the maxilla by a concavo-convex surface, while it is 

 immovably fixed to the pterygoid by its posterior extremity. 



The palatine is fixed to the anterior extremity of tlie pterygoid 

 by a ginglymus joint which allows considerable upward movement. 

 The pterygoid is loosely attached to the articular and quadrate by 

 ligaments, but there is not that close adhesion of the bones that is 

 said to occur in Crotalus, for instance. 



The mandible is attached to the quadrate by a ginglymus joint, 

 closely resembling that of the human elbow. The quadrate 

 stretches outwards, backwards, and slightly downwards, so as 

 to carry the posterior extremity of the mandible from the middle 

 line. The superior extremity of the quadrate articulates with the 

 squamosal by a large flattened surface, which allows of moderate 

 movement. The squamosal is firmly fixed to the side of the skull, 

 and is capable of only slight, if any, movement. 



The digastric acting on the posterior extremity of the mandible 

 in such a manner that the jaw is turned into a lever of the first 

 order. Owing to the length of the mandible from its anterior 

 extremity to the articular surface, and the shortness of the posterior 

 portion to which the muscle is attached, extended movement is 

 gained with loss of power. When, however, the mouth is closed by 

 bringing the mandible upwards, the lever is of the third order, 

 great power being gained by the insertion of the muscles along 

 the upper and middle portions of the bone. 



Since the mandible is carried outwards posteriorly, while it is 

 close to the middle line in front, it follows that, when the mandible 



