the horny envelope, while the pulp supplies the pith of the spine." [1]
The molar teeth are four on each side above and below, furnished with roots, nearly equal in size, nearly round in outline, covered at first with several tubercles, which when worn down present as many oblong layers of enamel on the crown of the tooth, while both the exterior and interior sides are marked by deep folds of the outer coat. The head is short and the muzzle abrupt; the eyes and ears are small, but the nostrils are large and open: the tongue is roughened with scaly prickles directed backwards: the clavicles (or collar-bones) are rudimentary, and hence the forelimbs have not the freedom of motion common to the families we have been considering: their motions are slow and ungraceful, and their form short, thick, and clumsy.
QUILL OF PORCUPINE.
The species of Hystricidæ, though not numerous, are extensively distributed; each great division of the globe has one or more representatives of the family, with the exception of Australia. Most of them are nocturnal animals of sluggish habits, living in burrows which they excavate for themselves. Some species, found in America, climb trees, as the genera Erethizon and Synætheres, the latter of which has the tip of the tail prehensile.
- ↑ Quadrupeds, p. 154
