SERPENTS. 



349 



and, by a special opening between tlie plates of the front of the mouth, can be 

 protruded while the jaws are closed ; in the Hydrophida; a special arrangement per- 

 mits this without admitting the water. The sense of taste is probably wanting, as 

 the reptile swallows its prey without mastication, though some forms crush it in the 

 coils of the body. All ophidians are carnivorous. 



The serpents are covered by an armature of scale-like folds of tlie skin, which 

 are ordinarily imbricated, though in some forms they are merely juxtaposed. The 

 armature of the lower surface of the body, in terrestrial forms, consists of a 

 series of transversely elongated scales, known as abdominal scutes, and the head is in 

 most cases protected by a regular arrangement of plates or shields. These shields, 

 modified or otherwise, and their arrangement, are of great value in determining spe- 

 cies, as they are very characteristic. The scales of the body are either smooth or 

 provided with one or more longitudinal ridges, or carinas, and are arranged in longitu- 

 dinal rows of equal number each side of the vertebral ridge, along which there is gen- 

 erally a more or less peculiar series, though in Stenostoma and Herpetodryas this row 

 is absent, making an even number of rows. In some forms, like JVaja, which distend 

 their necks, the number of rows in that region is increased. The ventral scutes are 



Fig. 207. — Upper, side, and lower views of bead of snal;e, to show the plates covering it. 1, rnstral ; 2, nasal ; 3, 

 loreal ; 4 preoculars or anteorbitals ; 5, postoculars or postorbitals ; 6, temporals ; 7, internasals ; 8, prefrontals ; 

 9, frontal ; 10, superciliary or supraocular ; 11, parietals ; 13, labials; 14, infralabials i 15, gular ; 16, mentals; 

 17. sub-mentals ; 18, ventrals ; 19, dorsals. 



ordinarily entire in outline, though in Dendrophidae they have a pair of notches, and 

 in Hydrophidje they are rejilaced by scales of the ordinary kind. As each of these 

 abdominal scutes is attached to a pair of ribs, their number corresponds with the 

 number of vertebra, and is hence of considerable diagnostic value. The scute 

 immediately in front of the anus is often divided, as are those underlying the tail, 

 the sub-caudals. 



Of the plates of the head it may be said that, as they vary but little in different 

 individuals of the same species, they are the most important factors in specific deter- 

 mination. They are named from the parts of the head which they jirotect. The 

 frontal scute overlies the frontal bones, and is generally entire ; posterior to it is the 

 pair of jjarietals, while anterior are the prefrontals, or, as they are sometimes called, 

 posterior nasals. Bordering on the parietals, frontal and prefrontals, and extending out 

 over the eyes, are the supraorbitals or supraciliary plates, while posterior to the pari- 

 etals are the generally scale-like occipitals. At the point of the snout is the rostral, 

 and lying between it and the prefrontals an; the internasals. The labials line the 

 upper lip, and in the pythons are deeply i)itted. The lower lip is similarly armed by 

 the infralabials. In front, the rostral is oi)p()sed to the mental or chin plate. Around the 

 eye are anteriorly the preorbitals, posteriorly the postorbitals, and, frequently, below the 



