. A text-book of agricultural zoology. Zoology, Economic. EODENTIA OE GNAWERS. 467 Eodents are characterised by having two long curved incisor teeth in each jaw (fig. 222, i); the crowns of these are continually 'being worn down, whilst growth as rapidly takes place at their roots. These teeth are employed in gnawing, and are more readily worn down behind than in front, so that they always present a sharp edge. This is due to the front having a plate of very hard enamel, whilst the back is composed of soft dentine. The lower jaw has never more than two incisors, the upper may have four. Canine
. A text-book of agricultural zoology. Zoology, Economic. EODENTIA OE GNAWERS. 467 Eodents are characterised by having two long curved incisor teeth in each jaw (fig. 222, i); the crowns of these are continually 'being worn down, whilst growth as rapidly takes place at their roots. These teeth are employed in gnawing, and are more readily worn down behind than in front, so that they always present a sharp edge. This is due to the front having a plate of very hard enamel, whilst the back is composed of soft dentine. The lower jaw has never more than two incisors, the upper may have four. Canines are never present; the molars and pre- molars are seldom more than four in number on each side of the jaw. The molars have flat crowns, the enamelled surfaces. Fig. 222.—Head of Rodent. The Hare (Lepits europtsus). i, incisors; pm^ premolars; m, molars. being in transverse ridges running across the teeth. The hind- feet are longer than the fore-feet, thus giving them the curious springing gait j the feet have usually five toes furnished with claws, but they may be reduced to four on each foot. The eyes are large and directed laterally. The brain has no convo- lutions, being nearly smooth. Many rodents have curious lateral " cheek-pouches " in which food can be stored for some little time ; when this food is required, the animal presses the pouches with its fore-feet. Most rodents are small animals, and feed upon vegetation. They are endowed with great repro- ductive faculties. The foetus is enclosed in a deciduate dis-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Theobald, Frederick Vincent, 1868-1930. Edinburgh and London, W. Blackwood and sons
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1899
