抄録
The purpose of this study was to make clear tlxe morphological changes in the skullsize, paritcularly the post-natal dexzelopment of the skull, of the Yezo brown bear (Urususarctos yezoensis lyd.) . The characteristics of development were classified into the growthof sizes, obliteration of suturae, and abrasion of teeth.All t]te skulls were measured by the method employed by SAITO (1963). As acriterion to tell the sex of a skull could be used the shape of temporal ridges and sagittalcrest of animals, or more of age, as was the case with American black bears observed byMARKS and ERICI<SON (1966). It was difficult, however, to differentiate the sex bythe shape of canine teeth. The results of measurement were analyzed statistically. The width of the craniunx(Eu-Eu) attained a maximum both in males and in females till twelve montlns of age. Itwas about 95mm. In the adult skulls, the mean value of the basilar length (B -P) was327tnm in males and 277mm in females. The sex difference was found to be very largein many items of the relative measurements, but the rate of mandibular length to basilarlength (Id -Cm/B -P) was comparatively constan?t. Its value was abottt 0.75. In theregressiwe liraes, oualy the rate of total length to basilar length (Op -P/B -P) showed posi-tixe growth. All the other rate showed negative growth.The skull of the adult bear contained the very large sinus [ror?talis. The morpho-oezaesis of the cranial sinuses was discussed to some extent.
