. On the anatomy of vertebrates [electronic resource] . rth premolar has a compressed tricuspidcrown. The dental formula of Gymnura is typical, viz. :— . c ^-z; p — ; 3^ 44. The dentition of our common Hedgehog {Erinaceus europceus)shows greater inequality in the upper and lower jaws, the formulabeing— . „„ _ nAAPoo? ™^ = 36, fig. 244. The first incisor in both upper and lower jaws is larger and longer than the rest, andis very deeply implantedin the jaw; the toothwhich follows the incisorsis small in both jaws,but especially so in thelowe
. On the anatomy of vertebrates [electronic resource] . rth premolar has a compressed tricuspidcrown. The dental formula of Gymnura is typical, viz. :— . c ^-z; p — ; 3^ 44. The dentition of our common Hedgehog {Erinaceus europceus)shows greater inequality in the upper and lower jaws, the formulabeing— . „„ _ nAAPoo? ™^ = 36, fig. 244. The first incisor in both upper and lower jaws is larger and longer than the rest, andis very deeply implantedin the jaw; the toothwhich follows the incisorsis small in both jaws,but especially so in thelower; it may be calleda canine with two rootsin the upper jaw, p last premolar is thelargest in both jaws ;above it has a quadri-cuspid crown with threefangs; below, a subcom-pressed tricuspid crownwith two fangs. The truemolars decrease in sizefrom the first to the thirdin both jaws, the firstand second have sub-quadrate four-pointed crowns, above; below, they are narrower,and the anterior and inner angle is produced into a fifth Dentition of Hedgehog. 1. Lower jaw, b side view, a working surface. 2. Upper jaw, a working surface, b side view. TEETH OF DIPHYODONTS. 309 The true molars of the tropical Hedgehogs, forming the sub-genera Echinops and Ericulus, are more simple, and approach theform of those in the Chrysochlore, being compressed from beforebackward, with two outer cusps and one inner cusp in the upperjaw, and with one outer and two inner cusps in the lowerjaw. The number of incisors is f-:f in both subgenera, which arefollowed by f-:J- small and simple premolars ; but Ericulus has f :-§-compressed tricuspid molars, and Echi?iops only -£-:£. The large Tenrecs or tailless Hedgehogs of Madagascar, com-bine the simple molars of Ericulus with the most formidablydeveloped canines which are to be met with in the whole orderInsectivora. The incisors are two in number in the upper jaw,but three in the lower jaw; very small and sub-equal in both;the ca
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