ANATOMY OF A SXAKE. 



303 



belly. It is by the action of the muscles on the ribs and scales that the Snake may be said to walk 

 on the ends of its very movable ribs. There are no traces of a shoulder girdle or of fore limbs in 

 Ophidia ; but the Blind Snakes, Rock Snakes, Boas, and Rollers have rudiments of a pelvis, and the 



SKELETON OF SNAKE, 

 (a) Anterior, (6) Posterior, view of Dorsal Vertebra. 



last have crooked bones terminated by claws externally. The nature of the skull will be considered 



in treating of the great groups. 



The beautiful scales on the body, and the regular plates and small scales on the heads of Serpents, 



are various in shape, number, ornamentation, and colouring, and they may or may not be keeled, and 



they overlap. All are thickened skin, and are covered with a delicate scarf skin. The plates on 



the head are on the same principle as those of Lizards, 

 but there are some others which are peculiar. 



The number of rows of scales on the top and sides 

 of the body and tail differs with the genus and species. 

 Usually there is a double row of scales on the under 

 surface of the tail, and the rest of the under surface 

 of the body has a continuous row of single broad scales, 

 Which are very striking in appearance, in contradistinction 

 to the others. 



At the moulting period the Snake is dull, lethargic, 

 and careless, and the outer scarf skin comes away as a 

 perfect scarf of the body and eyes. 



SCALES ON HEAD Ol' SNAKE (Styas feoiTOs). 

 (After Gunther.) 



r> Rostral; (/) Posterior and Anterior Frontil; (v) 

 Vertical; (s) Superciliary: (o) Occipiia'; (nn) Nasals: 

 (f) Loreal ; (o) Anterior Ocular or Orbital (Anteocdlar or 

 FneorbttW ; (p) Posterior Ocular or Orbital (Postocular 

 or Postorbital) ; (wl Upper Labials; (tt Temporals: (in) 

 Median Lowvr Labial or Mental ', [* *J Lower Labials; 

 (c) (.bin shields. 



SUB - ORDER THANATOPHIDIA.* THE 

 POISONOUS COLUBRINE SNAKES. 



The venom of a Snake is secreted by a gland on each 

 side of the front part of the skull, which is close to the 

 maxillary bones that support the long and more or less curved poison fangs. The duct of each gland 

 leads either to a groove in the front part of the fang, or to a canal in the tooth formed by the union of 

 the sides of a groove, and in both instances the liquid poison enters the victim with the tooth, and 

 some is left behind. Those Snakes which have the first fangs of the upper jaw grooved along their 

 front do not differ very much in their shape from the common innocuous Snakes, although some have 

 the power of expanding their neck into a kind of hood ; biit those which have the hollow teeth are 

 usually distinguishable by their large triangular head, short body, and very short tail, and are 

 viperiform. Thus two great divisions of the poisonous Snakes exist ; the first with grooved teeth the 



* flovoTos, death ; o^>u, a serpent. 



