Page:Natural History (1848).djvu/231

Rh the horny envelope, while the pulp eee the pith of the spine.”

The molar teeth are four on each side &#124; above and below, furnished with roots, nearly equal in size, nearly round in outline, covered at first with several tu- _bercles, which when worn down present as many oblong layers of enamel on the crown of the tooth, while both the ex- terior and interior sides are marked by deep folds of the outer coat. The head is short and the muzzle abrupt&#59; the eyes and ears are small, but the nos- trils are large and open: the tongue is ff roughened with scaly prickles directed &#124; backwards: the clavicles (or collar-bones)

are rudimentary, and hence the fore- limbs 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. &#124;

The species of Hystricida, though not 7 numerous, are extensively distributed

QUILL OF PORCUPINE. 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 slug- gish habits, living in burrows which they excavate for themselves. Some species, found in America, climb trees, as the genera Lrethizon and Syncetheres, the latter of which has the tip of the tail prehensile.