| THE RATTLESNAKE |
| (Crotalus horridus) |
| Beside the snake is the skin it has just discarded |
A large and very showy western analogue of the diamond-back, known by the sinister specific name atrox, occurs from central Texas to California. One of its varieties is red, with darker red markings and a white tail. The familiar rattlesnake of the plains east of the Rocky Mountains is Crotalus confluentus, which is of moderate size and dull hue; its mainstay of food is found among the prairie-dog towns. A similar but smaller species (C. oregonus) takes its place west of the Rockies, from British Columbia to southern California. The "tiger" rattlesnake, yellow barred with black; the "horned" rattler, which, like the Egyptian horned viper, has a trick of advancing sidewise, and consequently has the popular name "sidewinder"; and the slender green rattlesnake, are small species of the deserts along the Mexican border.
[CHAPTER XXII]
BIRDS—KINGS OF THE AIR
A bird is an animal clothed with feathers and having the forelimbs adapted to flight.
The birds constitute a class in the phylum Chordata, and otherwise are combined, in the group Sauropsida, with the Reptilia, with which they agree more closely in anatomy than with any other group, one prominent particular being that both have a single condyle, in contrast with the mammals and amphibians where the condyle is double. In fact primitive reptiles—probably of the stock of dinosaurs—are the ancestors of birds, the divergence having occurred probably in Carboniferous time. Of the earliest divergent forms, the rocks have as yet yielded no specimens, the most ancient bird forms recovered showing a degree of development in the new type that must have been preceded by a long history of evolution from its reptilian source.
