A Comparative Anatomical Study on the Mandibulae of Raccoon Dogs

A comparative anatomical study was made on 121 mandibulae (69 males and 52 females) of raccoon dogs captured in the northern Kyushu region. The results were as follows : 1. There are three mental foramens : anterior, middle, and posterior. The middle mental foramen was the largest with a diameter of 2.6mm. Its site of occurrence is between P_1 and P_2 and slightly lower than the center. The opening is mostly directed anteriorly. 2. Unlike the beagle dog's, the mandibular angle process is broad and roundish with a wide base. 3. The mandibular head index is about 38.1 and the mandibular head has an elongated elliptical form in the right and left directions. 4. The height of the condylar process is less than half that of the coronoid process. Consequently, the mandibular notch index is about 30.9, and the notch is quite shallow. 5. The mandibular ramus index is 74.3, which suggests that the coronoid process height against the mandibular ramus width is comparatively lower than that in the dogs. 6. The Thomson's mandibular index of the raccoon dog is 136.1, which is smaller than the dog's. This indicates that the mandibular length to the width is comparatively smaller in the raccoon dog than in the dogs. 7. The mandibular width index is 86.5. This is larger as compared with the dog's. This suggests that the width between the mandibular angles is comparatively larger than the width between the mandibular heads, as compared with the dog's. 8. Differences by sex for each measured item is slight as compared with the beagle dog's, which suggests the raccoon dog's primitiveness.