Abstract
The mandibles of 79 beagles bred under a given condition were measured and studied morphologically. In general, variations in morphology were few but differences by sex were significant. The results were as follows : 1. Dogs usually have three mental foramens. The largest was the middle mental foramen and its diameter was 6.0mm for male and 5.2mm for female. The middle mental foramen was positioned between P_1 and P_2 and slightly lower than the center. 2. At the mandibular ramus, the angle process protrudes outside the angle of the mandible. This was quite evident in dogs. As the index of angle process indicates, the angle process has a broad base and protrudes long and narrow. 3. The mandibular foramen was 8.4mm in diameter for male and 8.1mm for female and was positioned adjacent to the inferior border, much lower than man's, as the index of the mandibular foramen indicates. 4. The condyle of the mandible has its longitudinal axis from the posteroexternal to anterointernal direction. The index was 35.0 for male and 38.1 for female. Consequently, the form of the mandibular condyle is an elongated ellipse. 5. The height of the condylar process is only half that of the coronoid proccss. This is generally the characteristic morphology for the carnivora, which distinguishes the carnivora from man, herbivora, and omnivora. 6. Because of the marked difference in height between the coronoid process and condylar process, the mandibular notch is shallow. This is also verified by the low index. 7. Significant difference by sex was seen for most measured items excluding : angles, thickness of the mandibular condyle, height of condylar process, thickness of mandibular body, length of angle process, and diameter of the mandibular foramen. 8. The indexes calculated to determine relative relations between measured items of the mandible indicated the following : mandibular width is about two-thirds of the length ; mandibular width is widest between the mandibular condyles ; and width of mandibular angles is relatively small. In comparison with the height, the mandibular ramus and mandibular body were found to be wide.
