ビーグル犬の歯の形態学的研究

Abstract

A morphological study of teeth of beagle dogs was undertaken. The upper and lower teeth in 79 skulls were used and their crowns were measured and examined morphologically. The results were as follows : 1. Differences by sex in height, width, and thickness were recognized in most teeth. 2. For each item measured for the crown, of the incisor dentition, I_3 was the largest, followed by I_2 and I_1 in descending order, namely, the teeth became smaller from the distal to mesial sides. Of the molar dentition, carnassials (<P_4>___- and <M_1>^^^-) were the largest and the molars became smaller towards the mesial and distal sides. 3. Diastema in the maxilla was 4.62mm for male and 4.17mm for female, and in the mandible, 5.46mm for male and 5.28mm for female. The mandible was larger than the maxilla with a significant difference. 4. Development of the mesial and distal marginal tubercles was good in I_1 and I_2 but poor in I_3 in the maxilla. Inversely, in the mandible, the development was good in I_3 but poor in I_2 and I_1 in descending order. Also, no mesial tubercles were recognized in the mandible. 5. Development of the mesial and distal marginal tubercles of the mandibular premolars was quite poor in P_1 but better in P_2, P_3 and P_4 in ascending order. 6. Appearance of metaconus in the maxillary premolars was rarely observed in P_1 but was observed in more than a half of P_2 and in most of P_3 and P_4. 7. Appearance of hypoconid in the mandibular premolars was not observed in P_1 and barely observed in P_2. P_3 and P_4 showed quite high rates of appearance. 8. The morphology of the maxillary carnassials was compressed buccolingually and elongated mesiodistally, and consisted of three cusps, paracone, protocone, and metacone. Development of protocone was slightly lower as compared with that of racoon dogs. 9. The crowns of the maxillary distomolars consisted of four cusps, paracone, metacone, protocone, and hypocone. Occlusal surface indexes of talon of the maxillary distomolars for M_1 was 12.31 for male and 11.47 for female, and for M_2, 12.16 for male and 10.83 for female. These figures were quite small as compared with those of racoon dogs, and suggested that reduction in size of the talon in beagle dogs was extensive. 10. Metaconule and protoconule in the maxillary distomolars were observed in most of M_1. For M_2, the rate of their appearance was low and the degree of their development was also low. Hypoconule was observed in more than a half of M_1 but rarely observed in M_2. 11. The crown of the mandibular first distomolar consisted of five cusps, protoconid, metaconid, paraconid, hypoconid, and entoconid. Merely a tracing of paraconid was found in second distomolar and no paraconid was observed in third distomolar. Development of hypoconid and entoconid in third distomolar was very slight and could not be observed in many cases. However, metaconid was well developed in each tooth. 12. Relation in size of other teeth to carnassials was determined in index. The canines and the neighboring teeth of carnassials showed greater indexes for both jaws. However, the crown thickness index of the maxillary distomolars for M_1 was 163.09 for male and 168.15 for female, and for M_2 was 101.52 for male and 105.14 for female, and indicated that they were larger than carnassials in the crown thickness.