. A manual of zoology. Zoology. OOG CIIORDATA ap]iear in (lie eocene in the order CREODONTA, plLinti,i;ra(le forms wilh slia;htly dilYerenlialed denlilion; ihey resemble marsupials, inseclivores, as well as^llie'Condylarthra. True carnivores appear in the upi)er eocene. Order V. Rodentia. The rodents unite ^reat similarity in appearance with a characteristic dentition. The canines are absent, the molars separated by a lari^e ga]i (Jias- tciiia) from the incisors (fig. 614). The latter are strong, chisel-like, have per- sistent pulps and grow at "the root as they are worn away at the cutti
. A manual of zoology. Zoology. OOG CIIORDATA ap]iear in (lie eocene in the order CREODONTA, plLinti,i;ra(le forms wilh slia;htly dilYerenlialed denlilion; ihey resemble marsupials, inseclivores, as well as^llie'Condylarthra. True carnivores appear in the upi)er eocene. Order V. Rodentia. The rodents unite ^reat similarity in appearance with a characteristic dentition. The canines are absent, the molars separated by a lari^e ga]i (Jias- tciiia) from the incisors (fig. 614). The latter are strong, chisel-like, have per- sistent pulps and grow at "the root as they are worn away at the cutting edge. Since only the front surface has enamel^ wear keeps them constantly sharp. Usually there is but a single incisor; only the Duplicidentata have a second in tlie upper jaw. The molars are cuspidate or have enamel folds and frequently continue to grow throughout life. Their number is frequently reduced, the formula: varying between i'i il 3 and { S i' r. ISIany species have an inflected angle of the jaw like that of marsupials. The infraorbital canal is a striking feature in ISfurida; and Hystricicte (fig. 614, 0), a large opening in front of the orbit for a part of the masseter muscle. The rodents are distinguished from the ungulates by the smaller size, the possession of claws, five toes (sometimes reduced to three), the occurrence usually of a clavicle, and a discoid placenta. The mamma: are inguinal in position and are very numerous. The occur- rence of glands with a strong-smelling secretion, which ojien near the anus, is common (fig. 603). Over one thousand li\ing species are known, occurring in all regions except the Australian. The order appears in the eocene. Sub Order I. DUPLICIDENTATA (Lagomorpha), two upper incisors, in- cludes hares, Lcpiis/'' and picas, Lagoniys* Sub Order II. SCIUROMOR- The squirrels, , have soft fur and bushv tail. Sciiiriis* squirrels; Cyiioiiiys,'* prairie dogs; Scinro/ytcnis,'^ flying squirrels. The C.\stor- have s
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
