. An introduction to zoology : for the use of high schools . gradual loss first of the fifth, then ofthe second and fourth toes until the third alone is leftwith the rudiments referred to above. The earlier Equidse weie small, about the size of a fox, but they gained in sizet,ro 174 HIGH SCHOOL ZOOLOGY. during tlie Tertiary periotl until they attained the statuie of thehorses of the present day. 29. The great bulk of the Ungulates belong to the orderArtiodactyla, in wliich the third and fourth toes equallysupport the weight of the body. Here we have also primitiveforms, and specialised forms a
. An introduction to zoology : for the use of high schools . gradual loss first of the fifth, then ofthe second and fourth toes until the third alone is leftwith the rudiments referred to above. The earlier Equidse weie small, about the size of a fox, but they gained in sizet,ro 174 HIGH SCHOOL ZOOLOGY. during tlie Tertiary periotl until they attained the statuie of thehorses of the present day. 29. The great bulk of the Ungulates belong to the orderArtiodactyla, in wliich the third and fourth toes equallysupport the weight of the body. Here we have also primitiveforms, and specialised forms adapted for rapid locomotion ; theprimitive forms being, as in the last group, swamp loving oraquatic creatures, with comparatively hairless skin, and withteeth much more nearly approaching the tuberculate type thando those of the more specialised forms. As far as the dentitionis concerned, the swine are the most primitive of the livingspecies, but the Hippopotiimus is supported by all four toes, andtherefore, in this respect, it is the more primitive ri;;. 115.—Reduction of the lateral toes, and coalescence of metapodials into a can-non-lx)ne in Artiodactyla. (After Gaudry.) A, pi^; B, Hycemuschus; C, roe; D, antelope {Calotragug); E, sheep; F,embrjO calL These constitute two families, the Hipjiopotamidce and the Suidce,which differ from the remaiuing Artiodactyla in not chewing the first family has only a single genus, which, at the premie day, is HIGH SCHOOL ZOOLOGY. 175 represented by one or two species in the rivers of Africa. Their denti-tion is singular, for although the milk teeth are if, c}, na^, the adultshave only if, c^, nig, there being no permanent successors for one of themilk incisors and one of the milk molars. The peraiauent front teethare tusk-like, the incisors being straight, ?while the canines are curved,and meet each other in such a way, that the posterior faces of the muchlarger lower ones are ground flat against the anterior faces of the
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1889
