The Lower Jaw of a Squirrel
The backward and forward movement of the jaws and the great size and strength of the lower jaw, adapt rodents and gnawers to their mode of life, as in the squirrel. Labels: 1, The enamel of the gnawing tooth. 2, The ivory. 3, The lateral furrows of the molar teeth.
Cutter, Calvin First Book on Analytic Anatomy, Physiology and Hygiene, Human and Comparative (Philadelphia: J. B. Lippincott & Co., 1875) 67