1890.] HELODERMA SUSPECTUM. 215 



with rounded apex : a thin plate of cartilage, supported by the atlas, 

 prevents it from being in contact with the condyle of the occiput 

 during the life of the reptile. The postzygapophyses of this vertebra 

 face almost directly downwards, articulating with the counterfaced 

 prezygapophyses of the third cervical vertebra. From this point, 

 backwards, this is essentially the direction assumed by these articular 

 facets throughout the vertebral series. Passing next to the third 

 vertebra, it is seen to possess a form that, in its main features, agrees 

 with all the otlier vertebrae to the anterior sacral one. It is to be 

 observed, however, that they grow almost imperceptibly wider as 

 they are followed in that direction ; the last lumbar being the widest, 

 and the vertebra now under consideration the narrowest in its trans- 

 verse diameter. This third cervical vertebra has a peg-like and 

 conspicuous neural spine directed upwards and backwards. This is 

 also characteristic of all the vertebrae as far back as to include the 

 second caudal, from whence they gradually become thinner, more lofty 

 and pointed — to again become reduced and gradually disappear as 

 the few terminal joints of the tail are approached, wherein they are 

 quite suppressed. Rudimentary pleurapophysial prominences exist, 

 one upon either side of the fore part of the centrum of the third 

 cervical vertebra, but it does not develop the autogenous hypapophysis, 

 a character common to some lizards. Indeed there are no hypapo- 

 physes present upon the ventral aspects of the centra of the vertebrae 

 in Heloderma until we arrive at the first caudal one that bears a 

 chevron-bone. A subcircular intervertebral foramen is found between 

 the vertebrae for nearly the entire length of the column, it being 

 intended for the exit of the spinal series of nerves. It is of good 

 size where the brachial plexus comes out, but the largest apertures 

 are those between the last two lumbar vertebrae, or where the larger 

 branches of the lumbo-sacral plexus emerge, one upon either side. 

 The centra of the vertebrae, including the first caudal, are of 

 average length, rather broad, and flat upon their ventral aspects ; 

 the tail series beyond become gradually narrower, and comparatively 

 longer, as they diminish in size to the ultimate one. Facets for 

 articulation with the heads of the free vertebral pleurapophyses (of 

 those vertebrae that possess them) exist, one upon either side of all 

 the centra at their anterior parts. 



Choosing at random a dorsal vertebra from the middle of the series, 

 we are to note upon its superior aspect the thin anterior edge of its 

 neural spine and the almost equilateral outline that bounds its nearly 

 horizontal superficies. 



Apart from their largely developed lateral processes, the two free 

 sacral vertebrae agree in the main in their forms with the first caudal 

 vertebra. Their transverse processes are large, rounded, and thick, 

 with dilated outer ends, the bigger pair belonging to the anterior 

 vertebra. These outer extremities, upon either side, seize the ilium 

 between them, the anterior one having the superior hold, the posterior 

 one the under. Slender and rather conspicuous lateral processes 

 also characterize the caudal vertebras ; they are probably pleurapo- 

 physial developments. Gradually diminishing in size from first to 



[69] 



