INTRODUCTION. XXI 



serpentiform : its ribs increase in number, the anterior and 

 posterior limbs are removed farther and farther from each 

 other, and diminish in size and power, exhibiting in some 

 forms the anterior, and in others the posterior only, external 

 to the integument, until at length they cease to appear, being 

 merely rudimentary, and wholly covered by the skin. Of 

 this transition state we have an example in the common Slow- 

 worm, Anguis fragilis, which, though completely Serpenti- 

 form in its external appearance, yet possesses the minute 

 rudiments of limbs entirely concealed under the integuments. 

 Notwithstanding this general form of the Serpent, they have 

 not the expansible jaws of the true Serpents : nor is the cha- 

 racter of the ears the same, the tympanic membrane not 

 being superficial, nor the auditory passage covered by inte- 

 gument ; the eyes, also, like those of the Lizards, are fur- 

 nished with moveable eyelids, which are wholly wanting in 

 the true Serpents. 



Upon these characters, and several others of minor im- 

 portance, Mr. Gray founded his intermediate order of Sauro- 

 phidians, to comprehend all the transition forms ; but it may, 

 perhaps, be objected that the group is not sufficiently defined 

 to sanction such a distinction. On the other hand, it must 

 be confessed that it is difficult to reconcile the separation of 

 the Ophidians from the Saurians, according to the arrange- 

 ment of Cuvier, who, to effect this, has been obliged to place 

 some of these intermediate genera in the former, whilst he 

 retains others in the latter group. Upon the whole, as I 

 have before observed, it appears more consonant with nature 

 to consider, with Merrem, that the whole of these three 

 groups constitute but a single order. 



The movements of the Saurian reptiles are eflTected prin- 

 cipally by means of their feet, and in some of the higher 

 forms, exclusively so ; but as they descend towards the more 

 elongated form of the Scuiks, and other genera, in which 



