アライグマ (Procyon lotor) の下顎骨, 歯列弓, 口蓋および歯についての形態学的研究
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概要
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The mandible, upper and lower dental arches, palate, and upper and lower teeth were investigated morphologically with use of 15 raccoon skulls, and an anatomical examination in comparison with other mammals was made. The results were as follows : 1. The number of mental foramens varied from 3 to 9, and their sizes also varied. The mandibular foramen averaged 2.3mm in diameter and was located below the center. 2. The region where the masseters attached was well developed and the masseter fossa in particular was markedly developed. 3. The mandibular notch was shallow and the difference in height between the articular process and coronoid process was great. However, when compared with other mammals, the notch was rather deep and the difference between the two prosesses was small. 4. Between the three measured items -mandibular length, coronoid process height, and inter-madibular head width- significant positive correlations were found. 5. The dental arch index was 78.85 for the upper jaw and 66.54 for the lower jaw. In contrast with man, the dental arch length was greater than the dental arch width. The values however were larger in comparison with those of other mammals excluding the primates. 6. In the palatal form, the width appeared comparatively large against the height and length, in comparison with other mammals. 7. In the size of tooth, the most characteristic was the great height of the cuspids. However, the cuspids were small as compared with those of other mammals. 8. In the incisal teeth, I_3 was the largest, followed by I_2 and I_1 : closer to the mesial side, tooth was smaller. In the molars, the upper M_1 was the largest. This finding differed from the dog family in which P_4, a carnassial tooth, was the largest. In the lower jaw, M_1, a carnassial tooth, was the largest. However, in raccoons as compared with dogs, the development of M_1 was not too great. 9. In dogs, the crown width was greater than the crown thickness. In raccoons, however, the crown width was relatively small as against the thickness. 10. The upper carnassial tooth P_4 was not buccolingually compressed as in dogs. The crown consisted of 4 cusps and the occlusal surface rhombic. The retromolars did not show much difference from P_4. 11. The carnassial tooth M_1 of the lower jaw was not small in form as compared with the dogs'. The cuspal peak was not sharply pointed. The occlusal surface was mesiodistally elongated rectangular and consisted of 5 cusps. The talonid occupied more area than the trigonid. 12. One case each of supernummerary tooth and missing teeth was observed. The supernummerary tooth corresponded to the upper left third retromolar. The missing teeth were the right and left first premolars of the upper jaw. 13. Although raccoons are carnivorous in classification, they tend to be omnivorous. Therefore, their masticatory organs such as the mandible and teeth differ slightly from those of other carnivorous animals and present morphology adapted to their diet.
- 1984-12-25