OPHIDIA. 355 



a length equal to that of the body, club-shaped and viscose at the end ; 

 digits arranged in two bundles of two and three respectively ; eyes large 

 covered with a thick granular lid pierced by a small central opening for 

 the pupil ; they act independently of one another. Tympanum and 

 tympanic cavity absent ; skin with great power of changing colour ; * 

 skull with interorbital septum, without columella cranii (epipterygoid) ; 

 parietal single forming a crest and meeting posteriorly the supra-temporals 

 which connect it on each side with the squamosals ; parietal not moveable 

 upon occipital ; nasals narrow, not entering nasal apertures ; pterygoids 

 do not reach quadrate ; quadrate not moveable ; vertebrae procoelous ; 

 abdominal ribs present ; the tail is prehensile, coiling ventralwards, not 

 renewable ; the lungs end in several diverticula which extend far back 

 into the body cavity ; a few species are viviparous ; about 50 species, most 

 in Afr., Madagascar, a species in Socotra, another in S. Arabia, and a third 

 in India and Ceylon. Chamaeleon Laur., Afr., Madagascar, S. of Spain, 

 Arabia, India, Ceylon ; Ch. vulgaris, Daud., N. Afr., Syria., Asia Minor, 

 Andalusia, to one ft. ; Ch. pumilus Daud., to 5 or 6 in., S. Afr. : Ch. parsoni 

 Cuv., to two ft., Madagascar ; Brookesm Gr., Madagascar ; Rhampholeon 

 Gthr., trop. Afr. 



Order 4. OPHIDIA. t 



Elongated Reptiles without limbs, with horny epidermal scales 

 without osteoderms, with moveable quadrate bones, transverse anal 

 opening, and paired copulatory organs. Without eyelids, tympanic 

 cavity, urinary bladder and sacrum. The rami of the mandible 

 are united at the symphysis by an elastic ligament. 



Snakes are chiefly characterised by the absence of extremities, 

 and by the distensibility, which is sometimes extraordinary, of 

 the mouth and pharynx. They cannot however be sharply 

 separated from lizards. Formerly the limitations of this class 

 rested entirely upon the absence of limbs, and thus not only were 

 the Gymnophiona among the Amphibia, but also the blind worms 

 and other genera of apodal lizards included in it. Moreover 

 some snakes have traces of posterior limbs which are placed at 

 the root of the tail and carry a conical claw projecting at the 

 sides of the anus. 



* Thilenius, Morphol. Arbeiien, 7, 1897, p. 515; Keller, Arch. Physiol., 

 61, 1895, p. 123. 



f J. Miiller, " Ueb. eine eigenthiimliche Bewafmung des Zwischen 

 kiefers der reifen Embryonen der Schlangen u. Eidechsen," Mutter's 

 Arch., 1841 Dumeril et Bibron, " Erpetologie generale," Paris, 1854, 

 A. Giinther, " On the geographical distribution of Snakes," Proc. ZooL 

 Soc., 1858. Id. " The Reptiles of British India" London, Ray Society, 

 1864. ^G. Jan, " Iconographie generate des Ophidiens" Paris, 1860-82. 

 Lenz, " Schlangerikunde" ed. 2, Gotha, 1870. G. L. Boulenger, " Cata- 

 logue of Snakes in the British Museum,'" London, 1893-6. Huxley, Cope, 

 Zittel, Gadow, op. cit. 



