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Biomedical subjects

E G Wever

Publications and source records attributed to E G Wever.

At least 19 recordsLinked to original sources
PubMed1981

The role of the amphibians in the evolution of the vertebrate ear.

Serious question is raised concerning the commonly accepted view of the evolution of the vertebrate ear, which postulates a single line of development from fishes to mammals. The amphibian ear does not fit into this progression, for it differs both in basic structure and in the mechanics of operation. The amphibian ear is unique, and must have arisen from the labyrinthine structures of primitive fishes quite independently of the principal line that runs through the reptiles, birds, and mammals.

Amphibians↗
PubMed1979

Middle ear muscles of the frog.

The anuran middle ear in its complete form includes two skeletal elements, the columella and operculum, each occupying a portion of the oval window of the otic capsule and each provided with a middle ear muscle. The two elements have an interlocking arrangement of a form that makes it possible for these muscles to exercise a high degree of control of sound transmission from tympanic membrane to inner ear receptors. From the anatomical relations it is inferred that the two muscles operate as antagonists so that contraction of the opercular muscle and relaxation of the columellar muscle leave the columella free to move in and out of the oval window in response to sound vibrations, whereas a contraction of the columellar muscle and relaxation of the opercular muscle tend to immobilize the columella and reduce the transmission inward. The frog thus achieves a degree of control of sound reception that probably is unmatched among vertebrate ears. The purpose of the middle ear mechanism is no doubt the protection of the inner ear receptors (the amphibian and basilar papillae) from overstimulation by sounds, including the animal's own cries and the intense clamor produced by a group of frogs calling in chorus.

Animals↗
PubMed1978

Sound transmission in the salamander ear.

The mode of stimulation of the ear by sounds is considered in Amphibia, in which it differs among the three Recent orders. Of special interest is the order Caudata, in which this stimulation takes a unique form: sounds applied to the oval window of one ear produce a path of vibratory motion that passes through the brain cavity to the oval window on the opposite side. In this course the vibratory movements traverse both right and left amphibian papillae, and both basilar papillae also in species that contain these endorgans. Thus, in the salamander the hearing is invariably binaural.

Animals↗
PubMed1976

The caecilian ear: further observations.

The structure of the ear is examined in two species of caecilians, Ichthyophis glutinosus and I. orthoplicatus, and the sensitivity to aerial sounds is assessed in terms of the electrical potentials of the cochlea. The results are in general agreement with previous reports on other caecilian species.

Action Potentials↗
PubMed1976

Ear and hearing in Sphenodon punctatus.

Observations on Sphenodon punctatus have revealed new features of the anatomy of the ear,and measurements in a living specimen by means of cochlear potentials show the form and level of this ear's performance in sound reception. For an animal lacking an external ear opening and a functional tympanic membrane, the sensitivity of from 100-900 Hz is surprisingly good in low tones with peak response around 200-400 Hz. The inner ear is well developed, with a tectorial membrane connected to a tectorial plate that extends throughout the cochlea. The best region of sensitivity agrees well with the main frequency components of the animal's vocalizations.

Action Potentials↗
PubMed1975

The caecilian ear.

A study of the ear and its responses to acoustic stimuli was carried out in two caecilian species, Geotrypetes seraphini and Dermophis mexicanus. There is no external ear opening or tympanic membrane. The middle ear mechanism consists of a single element, the stapes, with its footplate in the oval window and a headpiece extending anterolaterally to the quadrate. The inner ear contains a single auditory endorgan, the amphibian papilla, somewhat similar to this organ in anurans. The mode of stimulation by sounds, however, involves a reentrant fluid circuit as in certain of the reptiles. In terms of the electrical potentials this ear is rather uniformly sensitive, though in low degree, to tones over the low-frequency range.

Acoustic Stimulation↗
PubMed1975

The amphisbaenian ear: Blanus cinereus and Diplometopon zarudnyi.

Observations on the structure and function of the ear in amphisbaenians have been extended to two new species: to Blanus cinereus of the family Amphisbaenidae and Diplometopon zarudnyi of the family Trogonophidae. Blanus, considered one of the most primitive of this group of reptiles, shows a distinctive form of sound-receptive mechanism. The usual extracolumella is lacking, and the columella attaches to a cartilaginous plate beneath the skin posterior to the facial area. Diplometopon zarudnyi, a highly modified trogonophid, shows a columella and extracolumella of massive dimensions, with considerable calcification of the latter process. Cochlear potential measurements revealed the levels of auditory sensitivity in these species. A peculiar feature is the degree of stability of the ear's responses in the presence of large variations in body temperature.

Animals↗
PubMed1973

The labyrinthine sense organs of the frog.

A study of the macula and crista organs of the frog's labyrinth with the use of an improved method of histological preparation has shown these endings to be more complex than heretofore believed. The structure lying over the layer of sensory and supporting cells is not a single "gelatinous" body as commonly described, but consists of two distinct layers with separate functions. In all these endings-macula sacculi, macula utriculi, macula lagenae, and the cristae of the three semicircular canals-there is a special tectorial structure that lies over the cellular surface and makes the connections to the ciliary tufts of the hair cells. It has the general form of a reticulum, though in the saccule it is somewhat elaborated.A preliminary study of other vertebrates indicates that this tectorial reticulum is present in all the labyrinthine endings throughout the series from fishes to mammals. Consideration is given to the possible advantages of this special tectorial structure in the stimulation process.

Amphibians↗
PubMed1972

Cochlear Structure in the Dolphin, Lagenorhynchus obliquidens.

The cochleas of five specimens of the Pacific white-sided dolphin, Lagenorhynchus obliquidens, that had been fixed by intravital perfusion, embedded in celloidin, and sectioned in a continuous series, were studied with particular attention to the numbers and distribution of hair cells and ganglion cells. The number of inner hair cells is estimated as 3272 and the number of outer hair cells is estimated as 12,899, for a total of 16,171 cells. The ganglion-cell population is estimated as 50,412 after correction for cell splitting in the sectioning process.

Journal Article↗
PubMed1972

The ear and hearing in Bipes biporus.

The sound conduction system of Bipes biporus is unusual among amphisbaenians, in that the columella does not have a catilaginous or bony extra-columella passing laterally to the labial skin. Instead, the terminal disk of the columella ends in fibrous tissue beneath a deep fold of skin forming the nuchal constriction. The occurrence of an epihyal supports earlier suggestions that the amphisbaenian extracolumella may be homologous to the epihyal. Measurements of cochlear potentials, made by direction of the sound stimuli to the region of the head posteroventral to the quadrate bone, show that Bipes biporus ranks high among amphisbaenians in auditory sensitivity.

Animals↗
PubMed1971

Periodical cicada: sound production and hearing.

The two main species intermingled in a brood of the 17-year cicada (Magicicada) have distinctive sound-making patterns and correspondingly different hearing abilities. Thus, they are acoustically isolated for mating purposes. Their simultaneous emergence and community "singing" has the important advantage of repelling predators.

Aggression↗
PubMed1971

The Cochlea of the Dolphin, Tursiops truncatus: General Morphology.

The anatomy of the cochlea of the dolphin Tursiops truncatus was studied in a number of specimens after fixation by vital perfusion, cellodin embedding, and serial sectioning. The results reveal the general structural relations and cellular detail up to the limits of light microscopy. A description is given of the variations of structure along the course of the cochlea, in which there are many departures from the typical mammalian form, especially in the compact quality of the tissues and the sturdiness of its elements. Apparently these features represent an adaptation of the cetacean ear to the reception of high-frequency sounds.

Journal Article↗