978 THE OSTEOLOGY AND MYOLOGY OF THE DEATH ADDER, 



the preceding vertebra. Lastly, we have the ball and socket joint 

 of the centrum. Thus we have five bony surfaces opposing ver- 

 tical movements anteriorly. On the other hand we have only 

 three opposing its movement downwards. To compensate for this, 

 we have the mechanical advantage of the ball and socket joint 

 alluded to in describing the centrum. Posteriorly we have five 

 surfaces opposing movement downwards, and three upwards. 

 The reason for this appears to rest in the fact that the spinalis 

 dorsi, semispinalis, and multifidus all run from behind forward, 

 and consequently when these muscles act they tend to pull the 

 vertebrae upwards and backwards, or in other words to cause them 

 to rotate round an axis placed at right angles to the long axis of 

 the body ; consequently the anterior portion of each vertebra will 

 be raised and the posterior will then endeavour to rotate, and thus 

 we have the five bony surfaces of each end of the vertebra to 

 resist the contractions of these muscles. 



Classification. 



As regards the classification of Acanthojjhis we have come to the 

 conclusion that its correct position is among the Elapidce. In 

 external appearance it bears a strong resemblance to a viperine 

 snake, and even the osseous elements of its skull tend to approach 

 the Solenoglyjohians. But when we examine the maxillary bone 

 we are no longer in doubt as to its real position. This bone has 

 undoubtedly the characters of the maxilla of the ProUroglypliians. 

 There are a number of anterior grooved fangs succeeded by a 

 number of small solid teeth. The size of the fangs is greater 

 than that usually found in the Elapidce. but this only corresponds 

 to the great strength of the bones composing the cranium ; while the 

 venom gland also appears to be larger, both absolutely and in pro- 

 portion, than is usual in the Elapidce. 



It would seem as if we had here a case of mimicry ; one of the 

 Elajndce taking on the external form of a viper, and with this 

 undergoing some slight internal modifications, but still remaining 

 undoubtedly among the Proteroglyphians. Or we may have in 

 Acanthophis a link between the venomous colubrine snakes and 

 the vipers. 



