Page:Popular Science Monthly Volume 4.djvu/277

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diameter. This is permitted by the extraordinary expansibility of their body; but the enlargement of their jaws is a complicated phenomenon. In the act of swallowing, they yield at every point, side-ways as well as vertically. The elastic integuments which hold the parts of their jaws in place give way, and the apparently small mouth becomes an enormous one.

Digestion proceeds slowly, and, if the meal be excessive, as it often is, the serpent remains sluggish and comparatively helpless a long time. "They have been kept four, six, and eight months, without being fed, and with very little apparent waste of substance." Bruce reports that he kept specimens of the cerastes, or horned-snake, two years in a glass vessel without food, during which time they cast their skins as usual.

Fig. 5.
PSM V04 D277 Reptile circulating system.jpg
Circulating System of Reptile.

a. Auricle receiving worn-out venous blood from the system; a'. Auricle receiving vitalized blood from the lung; v. Ventricle in which the two bloods are mixed, and from which it is thrown into the general circulation.

Vital activity in serpents is low. In mammals, the normal mean temperature is from 95° to 105° Fahr., and this must be maintained, or disease supervenes. With serpents, the temperature is a few degrees only above that of the surrounding atmosphere, and varies with it. Thus, it may range, in their healthy active state, from 60° to perhaps more than 80° Fahr. The temperature of a serpent was found, by Hunter and others, to be 88.46°, that of the air being 81.5°. The temperature of a frog was 48° in water at 44.4°. If the atmosphere be