The tympanic ring is asymmetrical. Compared to the length of crura, the stapes has a large base. Severtsov Institute of Ecology and Evolution Morphology of the Auditory and Vestibular Organs in Mammals, with Emphasis on Marine Species Galina N. The diameter and shape of the auditory meatus lumen vary Fig. The wide variety of experimental approaches will help readers to understand the broad range of issues related to inner ear morphogenesis and other concepts from complementary areas of investigation.
The radial osseous septa diverge from the tympanic ring and penetrate the whole tympanum. How it functions is less well understood, and with each new discovery, more questions arise. Fairchild, Ronald Bayer, and James Colgrove. The head of the malleus is massive. The precocial development of the cetacean inner ear complements previous work demonstrating precocial development of other cetacean anatomical features such as the locomotor muscles to facilitate swimming at the moment of birth. The main trends of structural evolution of the outer, middle, and inner ear were followed in representatives of different ecological groups during postnatal development.
The tympanic bone, together with the entotympanicum, form the tympanum, whose inner walls are smooth. Mysticeti Balaenoptera acutorostrata 163 1. The external auditory meatus has the shape of a curved tube 9 cm long and is surrounded by horseshoe-shaped cartilage. Pinnipedia Phocidae, Otariidae 39 1. The other type of ganglion cell innervates outer hair cells by means of long spiral fibers; each cell typically innervates many outer hair cells through the numerous angular enlargements and short end branches of its spiral fiber. The auditory meatus is surrounded by cartilaginous plates. The study of the embryo-genesis of the receptor structures of the vestibular apparatus in mammals with different ecological specializations is an important step to understand-ing commonalities in the development of struc-tures and functions of the inner ear of mammals and contributes to our understanding of the evolutionary origin of the labyrinth among vertebrates.
In the nutria, the upper edge of the auricle forms a fold located above the upper part of the auditory foramen. Special attention is paid to the least studied orders of marine mammals pinnipeds, cetaceans , being of great interest both with regards to the echolocating abilities in dolphins and the influence of the aquatic environment on the development of morphological adaptations in the structure of the outer, middle and inner ears. The tympanum is covered with a mucous membrane, which includes numerous blood vessels. The body of the incus is enlarged. This allows us to suggest the existence of a correlation between an effective functioning of the auricular mechanisms which close the auditory meatus when submerging under water and the degree of auricular gland development. All this provides information on the site of a sound source. There are cerumenal glands, which are simple-tubular in structure.
The auricle of the Northern fur seal Callorchinus ursinus is a thick leathery fold that can extend up to 5 cm along the long axis. Its short arm is quite reduced. The tunica media is composed of separate fascicles of unstriped muscle cells arranged in a circular order. The inner plate is 2 to 3 times thicker than the outer one and has a horseshoe-shaped form. A column-shaped formation is found where the long arm is connected to the wall of the tympanum. These data in combination with new insights into the echolocation ability of some shrews suggest that the evolution of echolocation in bats may involve inheritance of a primitive sonar system that was modified to its current state, rather than the ad hoc evolution of echolocation in the earliest bats. The location of the plates is similar to that in terrestrial carnivores.
The third day was limited to only ab out 65 invited scientists who were divided into topical working groups chaired by a rapporteur. Comparative-embryological studies of the peripheral part of acoustic system made it possible to determine the stages of formation of individual structures and establish general patterns of prenatal development of the organs of hearing and equilibrium in different mammals. Thus, the differentiation of biologically important frequencies in echolocating species occurs even at the level of the outer, middle and inner ears. Apical secretion of the apical part of the cytoplasm in the secretory cells is absent. As in most mammals, the middle part of the auditory meatus has a trumpet-like form with a top directed toward the tympanic bulla. Structure of the middle ear of mammals 45 2.
The presence of these glandular complexes in the skin of the auditory meatus is a specific characteristic and is not inherent for all representatives of the order. At the point of a knee-like bending, the lumen acquires a horseshoe-shaped form and is very narrow. George and Sam emerge from her narrative as distinct, wonderful, and at times frustrating children who both are autistic through and through. Egorov Available through our partner publisher Pensoft www. Y68 2008 Basic clinical neuroscience, 2nd ed. In the common dolphin Delphinus delphis , the auditory meatus is about 6 to 6. Special attention is paid to the least studied orders of marine mammals pinnipeds, cetaceans , being of great interest both with regards to the echolocating abilities in dolphins and the influence of the aquatic environment on the development of morphological adaptations in the structure of the outer, middle and inner ears.
Small alveolar and holocrine glands of complicated structure open into a nipple composed of an epidermal outgrowth. The joint between it and the wall of the tympanum is rigid. The manubrium is not widened in its proximal part. Category: Science Author : Stephen M. The tympanic and periotic bones appear to be isolated from each other and are approximately equal in size. The inner ear of mammals, unlike the outer and middle ears, is characterized by a variety of func-tions, while the structural organization is unvaried. In the brown four-eyed opossum Metachirops , the pars transversalis of the malleus is well developed.