FINE STRUCTURE AND SPLIT LINE OF HUMAN TEMPORAL BONES

Observations were made on 18 human temporal bones by making split lines and the structure of the substantia compacta was examined. Then the dynamic studies were made on them. 1) The outer surface. a) There were lines running from the anterior surface of the mastoid portion to the inner side of the external auditory canal. b) The lines originating from the tip of the mastoid portion run along the postero-superior part of the external auditory canal toward the antero-superior part. They joined together with their lines from the anterior and superior part of the squama, and run forwards along the axis of the zygomatic process. 2) The inner surface. The lines from backwards were consentrated to the pyramid. 3) The external auditory canal. The lines along the long axis turned at right angle on the tympanic ring and run along it. 4) The lines on the prominence of the lateral semicircular canal and the facial canal run along its long axis. 5) There were lines surrounding the oval window and the round window. 6) There were lines vertical in the promontory. 7) The osseus semicircular canal. In the inner surface of the semicircular canal, the ampulla had ring shaped lines running at right angle against the axis of cochlea and the crus had lines run obliquely against it. There were coiled lines winding to right on the semicirular canal of the right ear. 8) On the inner surface of the cochlea, there were ring shaped lines running at right angle against the long axis and those lines nearer the helicotrema showed tendency of the coil winding to right in the cochlea of the right ear. From direction of split lines, dynamic study was made on substantia compacta of the temporal bone.: 1) The outer surface of the temporal bone. The postero-superior wall of the external auditory canal had strong structure against the force- from the parietal and occipital region. 2) The external auditory canal. The ring of the ear drum had strong structure. 3) The margin of the oval window and the round window had a framework. 4) The semicircular canal had strong structure against the force which was given from the ampulla to the crus and the crus to the ampulla. 5) Any part in each winding of the cochlea had strong structure against the force given from various directions.