OF THE INTEGUMENTS. 75 



Tortrix scytale. They exist even in many serpents whose 

 heads are deprived of plates, and are replaced in others by 

 a circle of little scales. 



Two pairs of plates, the anterior and posterior Fron- 

 tals, cover, in the greatest number of Ophidians, the upper 

 part of the muzzle. Their form is, in a great measure, de- 

 termined by the lateral edges of that part, so as to be very 

 narrow in the Dryiophis, and \^^de in the Dipsas, &e. 

 The anterior are smaller than the posterior : they are 

 sometimes very small, as in many species of the genera 

 Lycodon, Dipsas, Elaps, Homalopsis, &c. ; in some of the 

 latter genus they are reduced to a single pair, wedged in 

 between or behind the nasals, which occupy their place ; 

 in the Hydrophis, the Tortrix, and the true Calamaria, 

 they totally disappear, and we then see but a single pair 

 of frontals. Their number, on the other hand, is in- 

 creased in other Ophidians, as in several Boas, the Trigo- 

 nocephalus hypnale, the Heterodon, and the Hydrophis 

 colubrina ; in other Boas, they are replaced by small 

 plates of an irregular figure, which are not distinguishable 

 from the scales. The modifications which these plates 

 undergo in the diverse races of Ophidians are numerous, 

 as may be seen in examining the figures in our plates. 



The muzzle of serpents is always terminated by a plate 

 more or less large, and always grooved below, to receive 

 the extremity of the lower jaw. The form of this Rostral 

 plate varies according to its use. It is most usually 

 pentagonal ; the size is determined by that of the muzzle ; 

 it is broad and very convex in most Ophidians ; in others, 

 as the Heterodon, the Naja hasmachates, the Eryx, many 

 Trigonocephali, &c., it is obliquely truncated down- 

 wards ; in the Dryiophis, it enters into the moveable ap- 

 pendix, with which the snout of that animal is pro- 

 vided. 



The Labials are those plates which garnish the edges of 

 the lips ; they are most frequently disposed in a single 

 row, sometimes in two or more rows, or rather, we find 

 several supernumerary plates, inserted between the labial 

 plates : this takes place in the Hydrophis, in several Ho- 



