TEGUMENTS OF REPTILES. 555 



ring lias a vital connection with the derm : it is caused to vibrate 

 by the muscles of the tail, and its vibration communicates a 

 quivering motion, accompanied by a rattling noise, to the dry 

 horny pieces behind it.' 



The pigment-cells are mostly combined with the epidermal 

 ones to form the deeper layers of the scales, and ornament the 

 skin of snakes with various and sometimes brilliant colours. The 

 poisonous serpents are mostly of a sombre hue. The periphery of 

 the derm is modelled according to the pattern, contiguous or im- 

 bricate, of the epiderm, the scales of which are evolved thereupon. 

 The blood-vessels form a beautiful and regular network, the area 

 corresponding with the shape of the scales, being lozenge-shaped, 

 e. g. in Coluber natrix^ with the uniting angle at the centre of 

 each scale. 



The skin of the snout developes tentacular appendages in Her- 

 jieton tentaculatum. The integument in the Cobras (^Naja) 

 expands into a broad fold on each side the neck : the folds are 

 supported by correspondingly elongated ribs, p. 55, fig. 46, pi. ; 

 when these are drawn forward an oval disc of skin is caused, sur- 

 passing the head in breadth, and usually rendered more conspicuous 

 by well-defined tracts of jMgment. The name of ' spectacle- 

 snake ' refers to the jiair of circidar spots connected by a ciu-ved 

 streak on the hood of the JVaia trijnidians. 



The secreting follicles of the skin in Serpents are chiefly con- 

 fined to certain depressions or inverted folds of the derm. These 

 in Crotalus and Trigonoccphalus constitute a pit between the 

 nostril and eye on each side of the head. The hinder scutes of 

 the lower lip have pits in Pi/thon Scldegelii ; as have those of both 

 lips in Python ametlujstinus. In AmphislxBna alba and in Chirotes 

 there is a row of pores in front of the vent. 



The skin in most Lacertians resembles that of Serpents : the 

 scales are thickened epiderm or horn ; in most imbricate, in a 

 few (yZonosaurus, V. der H.) verticillate ; usually smooth, but 

 in some carinate, and in some tubercvdate or gibbous : in a few 

 they support a spine at certain parts of the body, as, e. g. the 

 caudal scales of Zonurus, both dorsal and caudal scales of Tr- 

 bolonotus, the circumtympanic scales of Agama, the occipital 

 scales of Phrynosonia, and scattered dorsal and lateral scales in 

 the Australian Lacerta muricata of White. Bone is developed 

 at the base of the scale forming part thereof, or combining scute 

 and scale, in Ophisaurus, Tribolonotus, Tracliysaurus. In the 

 Chameleons the scales are small and thin, like grains. The 



,. , , ' coxcix. p. 294, pi. xii. « ^x. vol. iii. p. 241. 



