94 VERTEBRJ^: AND SKULL OF THE LIZAKD. 



boomerang, in the cyclodus; and have the median part of 

 the bend expanded and perforated in lacerta and scincus. 

 They are absent in the chameleon. 



The sacral vertebrae retain, in some lacertians, the cup- 

 and-ball joints ; and in these, e. g. the scincoids — in which 

 the centrums coalesce, the hind end of the second presents 

 a ball to the first caudal — not a cup, as in the crocodile. 

 In the cyclodus, the thick, short, straight pleurapophyses 

 are distinct at their origins from the two coalesced cen- 

 trums, but coalesce at their ends, that of the first sacral 

 being the thickest. In varanus and iguana, the pleurapo- 

 physes as well as the centrums, retain their distinctness, 

 but the hinder ribs incline forwards and touch the ex- 

 panded ends of the fore pair. These ends are very thick, 

 and are scooped out obliquely behind, so as to present a 

 curved border to the ilium, which Cuvier compares to a 

 horseshoe. 



In the varanus and iguana, the pleurapophyses of the 

 first caudal incline backwards as much as those of the 

 second sacral do forwards. In the cyclodus they extend 

 outwards, parallel with those of the sacral vertebrae, and 

 are longitudinally grooved beneath. Hsemapophyses are 

 wanting in the first caudal, are developed in the second, 

 and are displaced to the interval between this and the 

 third; they are confluent at their distal end, and pro- 

 duced into a long spine. At the twelfth tail- vertebra, the 

 line is obvious that indicates the extent of the anterior 

 detached piece, or epyphysis, of the centrum, immediately 

 in front of the origin of the diapophyses; it continues* 

 marking off the anterior third of the centrum in all the 

 other caudals. At this line the tail snaps off, when a 

 lizard escapes by the common ruse of leaving the part of 

 the tail by which it had been seized in the hands of the 



