Fig. 72.—A, Horny appendage (rattle) of Crotalus horridus (three-quarters natural size. After Garman). B, longitudinal section of the same. C, separated segments of the appendage: a, terminal point; h, basal segment (after Czermak).
The length of these animals often exceeds 2,000 millimetres. The head is flat, very large and expanded posteriorly, and terminated in front by a short, truncate snout; it is covered above with scales or small shields.
Rattle-Snakes are armed with enormous fangs enclosing a complete canal, which extends throughout almost their entire length. The poison-glands are of the size of a large almond.
The number of segments in the rattle is variable, but rarely exceeds 18 or 20. At the time of the shedding of the skin these segments fall off and are at once replaced. Contrary to the belief which was long entertained, their number bears no relation to the age of the snake.
Fig. 73.—Crotalus terrificus (Dog-faced Rattle-Snake, Cascavella in Brazil). (After Stejneger.)
Rattle-Snakes are met with especially in stony and arid localities, or among brushwood near water. They hardly ever bite except when surprised or attacked.
(1) C. terrificus (Dog-faced Rattle-Snake, Cascavella in Brazil; [fig. 73]).—Snout very short; three or four series of scales between the eye and the supralabial shields; body-scales in 23-31 rows, dorsals very strongly keeled; 160-199 ventrals; 18-30 subcaudals.
Colour brown, with a series of darker, light-edged rhombs, often lighter in the centre; a dark streak from the eye to the angle of the mouth; belly yellowish-white, uniform or spotted with brown; tail generally brown or blackish.