ヤギ (Capra hircus) の下顎歯と下顎骨についての比較解剖学的研究

概要

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Seventeen goats were used and bodys measurements of the mandibles and lower teeth were taken and a macroscopic morphological observation was made. An examination from the comparative anatomical viewpoint with other mammals was then made. The results were as follows : 1. In the occlusal form, the lower molar teeth were selenodont teeth peculiar to herbiborous animals. The anterior teeth were present only in the mandible. Eight teeth with three incisors and a canine on each side were positioned in a fan-shape. 2. There were three pairs of the lower premolars. P_1 was already regressed and disappeared and P_2 was small showing a regressive tendency. More mesially positioned a premolar was, the smaller its size was ; P_4 was the largest followed by P_3 and P_4 in descending order. 3. There were three pairs of the lower molars. More mesially positioned a molar was, the smaller its size was ; M_3 was the largest followed by M_2 and M_1 in descending order. Especially, the mesiodistal diameter of M_3 was larger in comparison with those of M_1 and M_2. The number of cusps was four for M_1 and M_2 and five for M_3. 4. The length of the cheektooth row was 76.58mm. The ratio of the molar row to the premolar row was about 67 : 33. The former was twice as long as the latter. The diastema between the canine and second premolar was 46.87mm, which was nearly twice the length of the premolar row. 5. The coronid process was higher than the condylar process with the ratio of about 4 : 3. The mandibular notch index was 51.86 and the notch depth was deeper than that for carnivora. These findings differ among various mammals. The difference is attributable to the difference in their food habits. 6. The height of the mandibular body was the highest, 38.59mm, at M_3 positioned most posteriorly. The height became lower toward the anterior side. The height was 14.51mm at the mental foramen. 7. The index for the ramus of the mandible was 28.62, indicating that the height is comparatively greater as compared with the width of the ramus. 8. The index for the head of the mandible was 36.27, indicating that the head thickness is greater in comparison with its length. This form, long in the right and left directions, appears to be a suitable morphology for masticatory movement for herbivora. 9. There was one mental foramen positioned on the outer surface of the mandibular body between the canine and second premolar. Its diameter was 3.17mm. In the vertical direction, it was positioned slightly higher than the center of the mandibular body. 10. The mandible foramen was 11.35mm in diameter and was positioned lower than the center of the mandibular ramus and close to the base of the mandible.
九州歯科学会の論文
1988-08-25

著者

今田吉紀
九州歯科大学口腔解剖学第1講座

ヤギ (Capra hircus) の下顎歯と下顎骨についての比較解剖学的研究

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