. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 214 COMPARATIVE MORPHOLOGY OF VERTEBRATES. arranged. When the teeth are adapted for cutting they are called secodont (cats, fig. 214); for crushing,bunodont (man); when mark- ed by transverse ridges, lophodont (elephants); when there are longitu- dinal crests, more or less crescentic in outline, they are selenodont (horse, fig. 216). In the triconodont tooth there are three prominences in the crown arranged in a straight line, parallel to the axis of the jaw. The middle and more prominent of these in the upper
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 214 COMPARATIVE MORPHOLOGY OF VERTEBRATES. arranged. When the teeth are adapted for cutting they are called secodont (cats, fig. 214); for crushing,bunodont (man); when mark- ed by transverse ridges, lophodont (elephants); when there are longitu- dinal crests, more or less crescentic in outline, they are selenodont (horse, fig. 216). In the triconodont tooth there are three prominences in the crown arranged in a straight line, parallel to the axis of the jaw. The middle and more prominent of these in the upper jaw is the protocone, with a smaller paracone in front and a metacone behind. In the lower jaw the corresponding terms are proto-, para-, and metaconid. In. FIG. 216.—A, triconodont tooth of Dromatherium; B, tritubercular tooth oiSpalaco- therium; C, interlocking of upper (dark) and lower (light) tritubercular molar teeth (after Osborn); D, molar of Erinaceus; E, of horse (selenodont type); c, cingulum; m, metacone (metaconid); p, paracone (paraconid); pr, protocone (protoconid); t, talon. a tritubercular tooth the three cones are arranged in a triangle, in such a way that they alternate in the two jaws, the protocone being on the inner side, the protoconid on the outer. Tritubercular teeth may have a lower projection (talon) on the hinder side. When this devel- ops into a prominent tubercle (hypocone, hypoconid) the tooth becomes quadritubercular. Then crests or lophs may develop, connecting the cones, so that the crown becomes ridged rather than tubercular. In the homodont dentition the number of teeth may be very large, varying from 100 to 200. With the heterodont dentition the number is smaller, the full dentition in the placental mammals including 44 teeth. From this number reduc- tions may occur by the loss of teeth of any kind. The number of teeth and of those of each kind is important in systematic work, and a dental formula has been devised to express this. As the nu
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