Search

In a series of 52 auditory ossicles, their structure and functional significance were studied, with special reference to the patterns of force transmission. The significance of the different degrees of cavitation in the ossicles as well as their eventual pathological significance are also discussed.

Adult and fetal human stapes were removed by means of the stereoscopic microscope in order to compare the size of the lamina or crista that joins the crura of the stapes and rests in the lateral aspect of the basis. 65 out of 110 specimens showed cristae of different sizes, whereas the remaining 35% did not possess this structure. The cristae were classified into large, medium-sized and rudimentary. Several incomplete or irregular structures were also found. The cristae or laminae divide the lateral aspect of the base into two fossae: a small upper one and a large lower one, although several variations were found. An edge of the pillar groove was usually continuous with the cristae; however, compact pillars were found at the point where they reach the base, where the cristae orginates. Asymmetrical cristae and changes in the general shape of the stapes were found in several specimens. Two ossicles showed crista with orifices due to resorption or to the passage of vessels.

The morphology of the external and the middle ear (auditory ossicles) in Chlamyphorus truncatus is influenced by its fossorial life. The external auditory canal consists of three parts. The most distal part is a short (cartilaginous) auricle which reaches anteriorly close behing the eye. Posteriorly to the auricle is a long, thin bony duct which consists of two segments, movable against each other. This tube leads through a narrow porus into the third part of the canal, the recessus meatus, which is enclosed in the bulla. The recessus with the narrow porus is characteristic for many fossorials and has a morphology with physical chracteristics of a resonator (HELMOHOLTZ). The malleus and the stapes in Ch. truncatus are also influenced by fossorial life. Based on the dorsal view of the malleus head, the Xenarthra can be divided into two groups. To the first division belong the Dasypodidae with Chlamyphorinae and Dasypodinae, to the second the Myrmecophagidae and Bradypodidae. The malleus of Cyclopes, a myrmecophagid, differs from that in the other Mymecophaginae and is similar to the malleus in the Dasypodinae. Two kinds of experiments should be undertaken: (a) physiologic-acoustic experiments in a fossorial to determine the effect of the recesses and (b) acoustic experiments varying the dimensions and positions of a tube and a porus leading into a resonator.

In a series of 100 cases, morphological variations of human ossicula tympani were studied. These have seldom been considered either in classic or recent descriptions. Among them, the malleus and stapes are the most variable ones. A geometric model is proposed to systematically study any variation from the typical ossicles. These morphological variations of ossicles could be related to age, sex, race, and could bring out peculiarities in acoustic transmission.