. A manual of zoology. Zoology. 570 CHORDATA tooth structure. The sin!,'Ie-toed horses appeared in the pleistocene with Fliohippiis (s) and then Eqiius itself (o). It is a jieeullar fact that the horse entirely died'out in America, althoui,di the chief part of its history was enacted here. The A:MBLYP0DA, mentioned above, were semi-plantigrade penta- dactvle forms, appearing in the lowest eocene, and reaching, in Vintalhcnum (Dhwccnis) an elephantine size. The TOXODOXTLV of the South American tcrtiaries combined perissodactvle, rodent, hyracoid, and proboscidian features, while the TILLODOXTIA
. A manual of zoology. Zoology. 570 CHORDATA tooth structure. The sin!,'Ie-toed horses appeared in the pleistocene with Fliohippiis (s) and then Eqiius itself (o). It is a jieeullar fact that the horse entirely died'out in America, althoui,di the chief part of its history was enacted here. The A:MBLYP0DA, mentioned above, were semi-plantigrade penta- dactvle forms, appearing in the lowest eocene, and reaching, in Vintalhcnum (Dhwccnis) an elephantine size. The TOXODOXTLV of the South American tcrtiaries combined perissodactvle, rodent, hyracoid, and proboscidian features, while the TILLODOXTIA of the eocene recall both carnivores and rodents. Order VII. Proboscidia. The elephants and their allies, with their hoofs and herbivorous dentition and lack of clavicle, are closely related to the ungulates. They are characterized bv their thick skin ('pachyderm'), the large, massive, five-toed legs, and espe- cially by the nose drawn'out into a long proboscis, lastly by the ^ dentition. Canines are lacking, but the incisors of the upper jaw continue to grow throughout life, forming the well-known tusks. In the living elephajits there are but a single pair of tusks, but in some extinct Mas- lodaiis there were a second smaller pair in the lower jaw, while Dinothcriiim had only the lower incisors, these projecting downwards. The molars (in Mastodon ^ , o T -I fi ffi,.,, •,„. and Dinothcriiim with normal replace- FlO. bib.—Inside ot Icitlouer )a\\ . ' of i„dicus, the alveoli opened ment and cusps) consist of numerous (after Owen), i, functional molar; 2, plates of enamel and dentine united by its successor. cement, and undergo a horizontal dis- placement. Of the three large molars and premolars only one at a time is functional (fig. 618, i); when worn out the next one behind (2) takes its place. Further features are a uterus bicornis, a zonary placenta, and two pectoral mamma;. Eleph.^: Elcplias iiidiciis, small ears; E. africaiins, large ears. E. priinigc
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
