Further observations on the ear in fossorial mammals with special considerations of Chlamyphorus truncatus (Harlan).

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.