Morphological studies of the skull of Yezo brown bear (Ursus arctos yezoensis Lyd). 2. Obliteration patterns of the suture and synchondroses of the skull

Abstract

In the morphological changes of the skulls of tlte Yezo brown bear (Ursus arctosyezoensis Lyd.) showing growth with postnatal development were observed the oblitera-tion patterns of suturae and synchondroses.The materials used in this study were the 56 skulls (36 male and 20 female)described in the previous part of the present series. The closing degrees of suturas andsynchondroses were determined by the method employed by FREDERIC (Table I).In both male and female skulls, the obliteration of sutrae and synchondroses wasobserved earlier in the intraoccipital synchondroses, sutura lambdoidea, and S. sagittalis.It is assumed that the crista sagittalis externa and the linea nuchae superior, which arepeculiar forms of the male adult skull, may have resulted from the ossification of theperiosteum, because tlaey developed cleary after the obliteration of S.lamboidea arndS. sagittalis.As the sex difference in the obliteration of suturae, it was unoticed that S. occipitomastoidea, S. squamosa, and S. sphenosquamosa had been closed later in the maleskulls than in the female.The sutura and synchondrosis which were not closed event in the oldest skull wereS. zygomaticotemporalis and synchorndrosis intersphenoidalis.It is reasonable to consider that the os sphenoidale can be divided into two portions: that is, os sphenoidale anterior and os sphenoidale posterior.In the bear skull, no S. nasomaxillaris has been formed. The same view as merntioned above seems to be observed in the skull of Lagomorplaa and Rodentia.