. The Australian zoologist. Zoology; Zoology; Zoology. ANDERSOX. Ill animals, as already mentioned, the two mandibular incisors make contact with one another only on their inner (lower) edges (PI. xv., fig. 3). The two oppos-. Fig. 3. Coelogenys paca, No. M. 3918. Dis- section by G. S'. Lightoller, showing the mylohyoid deep to m. transversus mandibiilae, from which it is separated by a well defined fascia, x 1/1. " G. S. Lightoller del. ing fairly sharp edges soon begin to exhibit signs of wear, which commences near the point as a narrow polished surface. This facet extends backwards and
. The Australian zoologist. Zoology; Zoology; Zoology. ANDERSOX. Ill animals, as already mentioned, the two mandibular incisors make contact with one another only on their inner (lower) edges (PI. xv., fig. 3). The two oppos-. Fig. 3. Coelogenys paca, No. M. 3918. Dis- section by G. S'. Lightoller, showing the mylohyoid deep to m. transversus mandibiilae, from which it is separated by a well defined fascia, x 1/1. " G. S. Lightoller del. ing fairly sharp edges soon begin to exhibit signs of wear, which commences near the point as a narrow polished surface. This facet extends backwards and widens so that in older animals the two teeth have a considerable area of con- tact in the median plane. The outer (upper) edges upon which the upper in- cisors work wear more rapidly and first develop a facet near the point, with a slope forward, downward, and outward. This in older animals becomes a shallow undulant depression on the upper surface elongated antero-posteriorly, and form- ing a horizontal truncation oblique to the long axis of the tooth (PI. xv., figs. 3, 4, 7, 8). In very old animals these two surfaces of wear meet at approxi- mately a right angle. At the same time the tooth has moved forward in its socket and the subcylindrical base has replaced the lanceolate anterior portion. It is for this reason that in old animals a considerable space intervenes between the bases of the lower incisors, since their horizontal diameters are now smaller at that point. In the upper incisors the earliest signs of wear appear on the inner edges (PI. xv., fig. 5), which develop a slight slope inwards where they come into eon- tact with the point and the outer edges of the lower incisors as these glide in- wards to reach the palatal pad. In very old animals the two lateral teeth be- come reduced to mere stumps, while the median incisor develops a downwardly directed sharp point in front, with a worn surface behind on a level with the abraded crowns of the two lateral incisors,
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1914
