ネコの頭蓋骨, 歯列弓, 口蓋および歯についての比較解剖学的研究

Abstract

With 20 skulls of Japanese cats as the material, the mandibula, upper and lower dental arch palate, and teeth were examined morphologically. Although they belong to carnivorous order, cats are said to have masticatory organs better suited for carnivorous diet than the members of the dog family. Therefore, the cats were examined in comparison with other mammals, particularly with carnivorous animals. The results were summarized as follows : 1. The cephalic length-width index for the cats was 70.72. The cats were brachycephalic whereas most of the animals in the dog family were mesocephalic. 2. Thomson's mandibula index for the cats was 97.09, which was lower than the index for bobcats and those for the members of the dog family. This finding indicated that the inter-mandibular head width was greater, although slightly, than the mandibular length in the mandibula of the cats. 3. In the palatal form of the cats, the width was relatively wider in proportion to the length and the height was markedly low as compared with those of other mammals. 4. The number of the transverse palatine folds was 8 in 71% and 7 in 29%. The folds got longer successively from the front to the back. However, the eighth fold was small and rudimental. 5. The dental arch index at M_1 was 114.88 for the maxilla and 98.60 for the mandibula. These values were markedly greater than those of other mammals and indicated that the width of the dental arch was relatively wide in proportion to the length of the dental arch. 6. Diastema was 3.47mm between I_3 and C, 2.83mm between C and P_2, and 2.00mm between P_2 and P_3 in the maxilla, and 7.03mm between C and P_3 in the mandibula. Unlike the members of the dog family, diastema was found between C and P_2 and between P_2 and P_3 in the maxilla in the cats. 7. The measurements of the crown height indicated that the paracone, 5.10mm at P_4 and 5.11mm at P_3, was the highest. The mesiodistal diameter was 10.13mm at P_4 6.54mm at P_3, and 3.31mm at M_1. The buccolingual diameter was 5.45mm at P_4, and 3.44mm at P_3, and 1.86mm at M_1. P_4 was the largest follwed by P_3 and M_1. 8. In the measurement of mandibular molars, the paraconid at M_1 and the protoconid at P_4 and P_3, 5.45mm, 5.11mm, and 4.41mm, respectively, were the highest. The mesiodistal diameter was 7.89mm at M_1, 6.97mm at P_4, and 5.42mm at P_3. The buccolingual diameter was 3.52mm at M_1, 3.06mm at P_4, and 2.59mm at P_3. The tooth size became successively smaller toward the front from M_1 to P_4 and P_3. 9. In the proportion of other molars to the carnassial tooth, P_3 was about 64% in the mesiodistal diameter and about 63% in the buccolingual diameter, and M_1 was about 32% in the mesiodistal diameter and about 34% in the buccolingual diameter, in the maxilla. Diminution percentage of M_1 was noticeable. In the mandibula, P_3 was about 69% in the mesiodistal diameter and about 74% in the buccolingual diameter, and P_4 was 88% in the mesiodistal diameter and about 87% in the buccolingual diameter. As compared with those in the maxilla, diminution percentage was small. 10. The coronal width-thickness index was 185.75 for P_4 in the maxilla and 224.47 for M_1 in the mandibula indicating that the mesiodistal diameter was markedly large in proportion to the buccolingual diameter.