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Objectives: An anatomical study was performed to describe the endoscopic anatomy and variations of the protympanum, including classification of the protiniculum and subtensor recess., Methods: A retrospective review was conducted of video recordings of cadaveric dissections and surgical procedures, which included visualisation of the protympanum, across 4 tertiary university referral centres over a 16-month period. A total of 97 ears were used in the analysis., Results: A quadrangular conformation of the protympanum was seen in 60 per cent of ears and a triangular conformation in 40 per cent. The protiniculum was type A (ridge) in 58 per cent, type B (bridge) in 23 per cent and type C (absent) in 19 per cent. The subtensor recess was type A (absent) in 30 per cent, type B (shallow) in 48 per cent and type C (deep) in 22 per cent., Conclusion: The protympanum is an area that has been ignored for many years because of difficulties in visualising it with an operating microscope. However, modern endoscopic equipment has changed this, providing detailed anatomical knowledge fundamental to ensuring the safety of endoscopic surgical procedures in the region.

The existence of hard tissue pulleys that act to change the direction of a muscle insertion tendon is well known in the human body. These include (1) the trochlea for the extraocular obliquus superior muscle, (2) the pterygoid hamulus for the tensor veli palatini muscle, (3) the deep sulcus on the plantar aspect of the cuboid bone for the peroneus longus tendon, (4) the lesser sciatic notch for the obturator internus muscle, and (5) the bony trochleariformis process for the tensor tympani muscle tendon. In addition, (6) the stapedius muscle tendon shows a lesser or greater angulation at the pyramidal eminence of the temporal bone. Our recent studies have shown that the development of pulleys Nos. 1 and 2 can be explained by a change in the topographical relationship between the pulley and the tendon, that of pulley No. 3 by the rapidly growing calcaneus pushing the tendon, and that of pulley No. 4 by migration of the insertion along the sciatic nerve and gluteus medius tendon. Therefore, in Nos. 1-4, an initially direct tendon curves secondarily and obtains an attachment to the pulley. In case No. 6, the terminal part of the stapedius tendon originates secondarily from the interzone mesenchymal tissue of the incudostapedial joint. In the case of pulley No. 5, we newly demonstrated that its initial phase of development was similar to No. 6, but the tensor tympani tendon achieved a right-angled turn under guidance by a specific fibrous tissue and it migrated along the growing malleus manubrium., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Some researchers contend that in adults the tensor tympani muscle (TT) connects with the tensor veli palatini muscle (TVP) by an intermediate tendon, in disagreement with the other researchers. To resolve this controversy, we examined serial sections of 50 human embryos and fetuses at 6-17 weeks of development. At 6 weeks, in the first pharyngeal arch, a mesenchymal connection was found first to divide a single anlage into the TT and TVP. At and after 7 weeks, the TT was connected continuously with the TVP by a definite tendinous tissue mediolaterally crossing the pharyngotympanic tube. At 11 weeks another fascia was visible covering the cranial and lateral sides of the tube. This "gonial fascia" had two thickened borders: the superior one corresponded to a part of the connecting tendon between the TT and TVP; the inferior one was a fibrous band ending at the os goniale near the lateral end of the TVP. In association with the gonial fascia, the fetal TT and TVP seemed to provide a functional complex. The TT-TVP complex might first help elevate the palatal shelves in association with the developing tongue. Next, the tubal passage, maintained by contraction of the muscle complex, seems to facilitate the removal of loose mesenchymal tissues from the tympanic cavity. Third, the muscle complex most likely determined the final morphology of the pterygoid process. Consequently, despite the controversial morphologies in adults, the TT and TVP seemed to make a single digastric muscle acting for the morphogenesis of the cranial base., (© 2016 Wiley Periodicals, Inc.)

Substance P-immunoreactive nerve fiber (SP-IR NF) and calcitonin gene-related peptide-immunoreactive nerve fiber (CGRP-IR NF) are important mediators of neurogenic inflammation and blood supply. SP-IR and CGRP-IR NFs in the tensor tympani muscle (TTM) of the human middle ear have yet to be described. In this study, the TTM, tympanic membrane, malleus in the middle ear and tensor veli palatini muscle (TVPM) were examined by whole-mount immunohistochemistry in tissue from Japanese subjects. Thirteen human cadavers (ranging in age from 46 to 90 years) were used in this study. SP-IR and CGRP-IR NFs were primarily found on vessels at the origin, insertion and belly of the surface of the TTM and on the internal surface of the tympanic membrane. These neural factors were also detected on the surface of the malleus and the insertion of the TVPM. Therefore, our results indicate that existence of the SP-IR and CGRP-IR NFs of the TTM and the TVPM may reflect muscle properties involved in pain or inflammation of the middle ear.

In order to improve realism in middle ear (ME) finite-element modeling (FEM), comprehensive and precise morphological data are needed. To date, micro-scale X-ray computed tomography (μCT) recordings have been used as geometric input data for FEM models of the ME ossicles. Previously, attempts were made to obtain these data on ME soft tissue structures as well. However, due to low X-ray absorption of soft tissue, quality of these images is limited. Another popular approach is using histological sections as data for 3D models, delivering high in-plane resolution for the sections, but the technique is destructive in nature and registration of the sections is difficult. We combine data from high-resolution μCT recordings with data from high-resolution orthogonal-plane fluorescence optical-sectioning microscopy (OPFOS), both obtained on the same gerbil specimen. State-of-the-art μCT delivers high-resolution data on the 3D shape of ossicles and other ME bony structures, while the OPFOS setup generates data of unprecedented quality both on bone and soft tissue ME structures. Each of these techniques is tomographic and non-destructive and delivers sets of automatically aligned virtual sections. The datasets coming from different techniques need to be registered with respect to each other. By combining both datasets, we obtain a complete high-resolution morphological model of all functional components in the gerbil ME. The resulting 3D model can be readily imported in FEM software and is made freely available to the research community. In this paper, we discuss the methods used, present the resulting merged model, and discuss the morphological properties of the soft tissue structures, such as muscles and ligaments.

The topographical relationship of the chorda tympani nerve (chorda tympani) to the tensor tympani muscle in the middle ear of carnivores provides new phylogenetic information. The examination of histological serial sections of 16 carnivore species representing most families revealed two distinct character states concerning the course of the chorda tympani: a hypotensoric state with the nerve running below the insertion tendon of the tensor tympani muscle, and an epitensoric state with the nerve running above the tendon. The shift from the plesiomorphic hypotensoric chorda tympani to the apomorphic epitensoric condition occurred once in carnivore phylogeny: Only in the herpestid species under study does the chorda tympani cross above the tensor tympani muscle. Therefore, we introduce the epitensoric pattern as a new synapomorphy for herpestids. Within the herpestids we find the following structural distinctions: Herpestes javanicus and Galerella sanguinea have a chorda tympani running in a sulcus directly above the insertion of the tensor tympani muscle, whereas in the eusocial herpestid species Suricata suricatta and Mungos mungo the chorda tympani lies far above the insertion of the muscle., ((c) 2009 Wiley-Liss, Inc.)

Study Design: This work reviews the literature concerning the life and scientific contributions of Hieronymous Fabricius (1533-1619). We also analyze the translated Latin text that focuses on the middle ear muscles from a first edition of Fabricius' book entitled 'De Visione, Voce et Auditu' (The Vision, Voice and Hearing, 1600)., Results: Hieronymous Fabricius was one of the first scientists to introduce structure-function relationships in anatomic research. Better known for his descriptions of venous valves and human fetal development, his major contribution to otology was his theory on tensor tympani (TT) function. The TT is 1 of 2 middle ear muscles whose function has undergone a long period of speculation since its discovery by Vesalius (1514-1564) and description by Eustachius (1510-1574). Fabricius' theory of TT physiology was described in his treatise 'De Visione, Voce et Auditu' (1600). He wrote that the TT "protected" the tympanic membrane and helped in middle ear ventilation. In the 20th century, the development of the acoustic impedance measuring bridge by Otto Metz (1905-1993) allowed for the first objective measurements of middle ear function. Experiments on human subjects with various ear pathologies confirmed that the stapedius was the dominant sound evoked middle ear muscle. However, Fabricius' original theory on the TT's role in middle ear ventilation persists to this day based on recent physiologic, embryologic, and histologic studies., Conclusion: Hieronymous Fabricius was a pioneer in approaching anatomy from a structure-function relationship, and was an active proponent for maximizing the learning environment for students. Fabricius' writings provided the foundation for contemporary theories on the role of the TT, and he proposed those ideas during an era when great strides were being made to increase our understanding of ear anatomy and physiology.

Introduction and Objectives: Temporomandibular disorders are associated with symptoms such as tinnitus, vertigo, sensation of hearing loss, ear fullness and otalgia. The connection and dysfunction of the tensor tympani and tensor veli palatini muscles seems to be associated with the aforementioned symptoms. We seek to demonstrate and explain this connection through the morphometry of these structures., Methods: We studied 22 paired blocks and 1 left side of human temporal bone. Digital measurements were made of the tensor tympani muscles and stapes., Results: The average length of the stapedial muscle was 5.8 mm SD 0.61, and that of the tensor tympani was 19.69 mm SD 1.07. Anatomical connections were found in all the samples between the tensor veli palatini muscles through a common tendon., Conclusions: There is a need for an interdisciplinary management between physician and specialized dentist in cases of craniofacial pain., (2009 Elsevier España, S.L. All rights reserved.)

In students' dissection practice, it is very difficult to teach students the structures and functions of the middle ear ossicles. The middle ear ossicles are too small to explain their structures and functions. Models are useful in explaining these points, but there have been no models that accurately explain the movements of the middle ear ossicles and the functions of the muscles in the middle ear. This time, we have made a model of middle ear ossicles. Our ear ossicles are made of paper-mache with metal in it. The incudomalleolar and incudostapedial articulations are made of rubber. The tensor tympani and the stapedius muscles are made of wire and the two wires can be fixed by cord stoppers. Our model explains clearly the following mechanisms of the middle ear ossicles. 1. The mechanism of sound conduction system. When the sound vibrates the tympanic membrane, malleus and incus rotate together. The long process of the incus pushes the head of the stapes. The sound is amplified by leverage. 2. Attenuation of sound by contractions of tensor tympani and stapedius muscles. When a loud sound is transmitted through the ossicular system, the tensor tympani muscle pulls the malleus inward while the stapedius muscle pulls the stapes outward. These two forces oppose each other and increase rigidity of the ossicular system, thus reducing the ossicular conduction. 3. The mechanism of how paralysis of stapedius muscle, caused by an injury to the facial nerve, results in hyperacusis. 4. This model also suggests a possible reason why the pars lucida of the tympanic membrane exists.

Systematic anatomical description of the various structures of the temporal bone have been performed based on dissection of 16 guinea pigs (32 temporal bones). It has been found that besides two main air spaces in the middle ear, the tympanic bulla and dorsal bulla described in literature, there are also additional air cells in the mastoid process and facial nerve region in the temporal bone of a guinea pig. Moreover recesses were found in the walls of the tympanic bulla that formed almost completely separated partitions of tympanic cavity. The malleus head, the body of the incus and the superior and lateral semicircular canals as well as the facial nerve are easily accessible from the dorsal bulla. From the ventral tympanic bulla, one can access both windows and the cochlea. The semicircular canals are relatively large, the lateral canal is largest and the posterior the smallest. The cochlea has thin bony wall, and is composed of 3.5-3.75 turns.

The discussion among anatomists and otolaryngologists about the muscles originating from the Eustachian tube and the connections between the tensor tympani and tensor veli palatini muscles started in the 1860s. From then on, a considerable number of contradictory hypotheses and data have been presented. However, before discussing whether or not these two muscles form a functional unit, interest should focus on the question of whether it is even possible. The cartilaginous portion of the Eustachian tube with all muscles originating from it, including the whole tensor tympani muscle, was dissected from five perfusion-fixed cadavers and removed in toto. Complete longitudinal serial sections of 10 microm were made in the axis of the tensor tympani muscle. Sections were alternatingly stained according to Cason's and Maskar's techniques. The macroscopic aspect (under the operating microscope) of a tendinous connection between the two muscles under consideration could be proven by the histochemical methods used in all cases. Based on our findings and the literature reviewed we are convinced that the tensor tympani and tensor veli palatini muscles of man constitute a functional unit. This represents an important step forward towards the understanding of the possible functions the tensor tympani muscle serve in man.

Objective: The fetal development of the supratubal recess and of the tensor fold was described by Hammar in 1902. Recent studies claim that neither structure is regularly present in neonates and controversial views have been presented of the separation of the anterior attic and supratubal recess. The objective of this study is to clarify these issues., Methods: Twenty temporal bones, 13 neonate and seven infant, were studied either by microdissection of fresh (five bones) or formalin stored (two) specimens, or by serial sectioning after formalin fixation and decalcification (13 bones). The serial sections were cut to 20 microm, every tenth section saved and stained by hematoxylin eosin., Results: In all specimens the separating structure between the anterior attic and supratubal recess was the tensor fold. It was intact in 15 bones while five showed a membrane defect. In vertically oriented folds the recess was deep and in horizontally oriented folds shallow. In 19 bones the tensor fold inserted superiorly to a soft tissue insertion ring of varying thickness and only once directly to a shallow transverse crest. The breadth of the tensor fold near the tensor tendon showed only little variation, whereas its height, and the distance from the tensor tendon to the supratubal tegmen varied in larger limits., Conclusions: The tensor fold and the supratubal recess are present already in the neonate and thus develop during the fetal period. The shape of the recess is determined by the fold direction and its size grows in conjunction with the other middle ear spaces. The transverse crest has no apparent influence on the position of the tensor fold. The easiest method to study the integrated whole of the anterior attic and supratubal recess is to view them alternatively from the anterior and superior microdissection approaches. Clinically, removal of the tensor fold creates an efficient additional aeration route from the supratubal recess to the anterior attic.

Although the middle ear muscles have been described for the first time more than four hundred years ago their role in modulation and transmission of sound is not yet fully understood. Surprisingly very little is known about proprioceptors in these muscles, especially in man, although this seems to be the key to the understanding of their various functions. Therefore, the question for proprioceptive sensory organs in these muscles is still relevant. The tensor tympani and stapedius muscles of four women who had donated their bodies to our institute were taken. Complete serial sections of these muscles were made which were either impregnated with silver, stained with ferric oxide for acidic polysaccharides or incubated with antibodies against S-100 protein. Thereby four to eight (mean five) muscle spindles distributed along the whole muscle could be detected in the tensor tympani muscles. These spindles contain one to three intrafusal muscle fibres and their length ranges from 140 to 4270 microm (mean 1492.8 microm). Furthermore, in three stapedius muscles one to two (mean 1.7) muscle spindles were found. They were from 350 to 500 microm (mean 482 microm) long and contained only one intrafusal muscle fiber. Regarding the diameter of intrafusal muscle fibers in both, the tensor tympani as well as the stapedius muscle, no difference to extrafusal muscle fibers of these muscles could be detected. The structure of these spindles differs considerably from those found in skeletal muscles. The morphological findings presented strongly suggest that muscle spindles occur regularly in both middle ear muscles. The results presented herein are consistent with clinical findings obtained from electromyographic studies and may help to elucidate all functions the middle ear muscles might serve in man.

In a gross anatomic study of 20 sides in 16 human head specimens, the tensor veli palatini, the dilatator tubae, and the tensor tympani muscles were studied. The tensor veli palatini was observed to insert onto the anterior one-third of the pterygoid hamulus, whereas the dilatator tubae rounded the middle one-third of the pterygoid hamulus without an insertion. Thus, the dilatator tubae, not the tensor veli palatini, could serve to tense the anterior velum. An insertion from the superior pharyngeal constrictor muscle onto the posterior one-third of the hamulus could provide a curbing function for the dilatator tubae muscle. Adipose tissue, located at the hamulus, could provide lubrication for the tendinous fibers of the dilatator tubae as they round the hamulus. The dilatator tubae was observed to attach to the hook of the eustachian tube and is accepted as the tubal dilator. Observed on 13 of 20 sides in 11 specimens, the bulk of the dilatator tubae remained distinct from the tensor veli palatini despite a connective tissue alliance and intermingling of some muscle fibers. On 5 of 20 sides in 5 specimens, fibers of the dilatator tubae intermingled extensively with the tensor veli palatini. Of the 20 dilatator tubae muscles dissected, 2 were observed to be deficient. The tensor veli palatini was observed to be continuous with the tensor tympani. Full color versions of the figures are available at the following website: http://www.shc.uiowa.edu/papers/tensor/.

This study was designed to aid experimental otologic studies of the rat middle ear. The topographic anatomy of the albino rat middle ear is described. A set of microphotographs with matching illustrations presents the structural details at several surgical exposures. Anatomic differences between the rat, guinea pig, and cat are noted.

Hypothesis: The aim of this study was to investigate the anatomy and pathology of the anterior epitympanum and of the tensor fold., Background: Early studies reported data that are primarily still relevant, but contemporary reports present conflicting data, including several erroneous concepts., Methods: Fifty-one temporal bones were dissected, and the anatomic details were photographed in 42 normal and nine infected bones. Histology was documented from seven serially sectioned bones, five normal and two infected., Results: The tensor fold formed the frontal wall of the anterior epitympanum between tensor tendon and attic bony wall, the anterior insertion consisting of composite connective and fatty tissue with some bone trabeculae. The transverse crest was posterior to it and extended from the anterior tympanic spine to the facial canal. The tensor fold angle in 78% of the specimens was between 45 degrees and 80 degrees, seldom horizontal, and the size of the supratubal recess (or space) increased as the fold angle increased. In 14 ears (27%) the fold had a membrane defect connecting the two spaces. Blockade of the tympanic isthmus caused inflammatory obliteration of the anterior epitympanum when the tensor fold was intact., Conclusions: The anterior epitympanum, a closed space around the anterior half of the head of the malleus, is normally closed by an intact tensor fold, but about one fourth of ears may show membrane defects. Aeration occurs via the tympanic isthmus through a constriction formed by the head of the malleus with the medial attic wall. In surgery for ears with epitympanal pathology, incus transposition should be combined with resection of the thin portion of the tensor fold for safeguarding permanent attic aeration.

The epitympanic compartments and the anatomy of the atticotympanic diaphragm were examined in a pair of serially sectioned temporal bones with secretory otitis media and chronic otitis media, respectively. Findings confirmed reports of 19th century scientists in that Prussak's space has a wide connection to the mesotympanum through the posterior pouch of Tröltsch and may have an additional narrow passage in its roof to the lateral malleal space. The lateral incudomalleal fold regularly separates the upper lateral attic from the lower lateral attic and the mesotympanum. The medial incudal fold as a rule is atrophic already at birth. The anterior tympanic isthmus thus extends from the tensor tympani tendon to the posterior incudal ligament and is the main passage for epitympanic and mastoid aeration. Opening(s) in the tensor fold, when present, are also important. In some ears, the posterior tympanic isthmus may form an auxiliary narrow route for aeration via the incudal fossa. The isthmi may be blocked by middle ear infection, which can lead to chronic mastoid and attic disease. Pathways for cholesteatoma spread in the epitympanum are discussed.

The brain stem position, organization and number of motoneurons innervating the rabbit tensor tympani muscle (TTM) were determined by retrograde axonal transport of cholera toxin B/horseradish peroxidase conjugate (CTB-HRP) and wheat germ agglutinin HRP conjugate (WGA-HRP) tracers. The synaptic input to the TTM motoneurons was examined with WGA-HRP. The results show the motoneurons of the TTM to be localized in a cluster ventro-lateral to the outer margin of the ipsilateral trigeminal motor nucleus (VMN) and dorso-lateral to the superior olive. The number of labeled cells was greater in the combined CTB-HRP/WGA-HRP injected cases. The TTM motoneurons were triangular and elongated in shape and smaller than those of the VMN. An extensive network of dendritic branches was present ventro-laterally in the vicinity of the superior olive. Similar, but less extensive collections of dendritic processes were observed to course dorso-medially, rostrally and caudally. Axons were observed to project first dorsally or laterally, towards the trigeminal motor root, then after a sharp turn coursed ventrally within the trigeminal motor root (VMR). Transneuronal transport of the WGA-HRP was not accomplished in any preparation, suggesting among other things, system or species differences in the effectiveness of the WGA-HRP conjugate as a transynaptic tracer. It is concluded that the TTM acoustic reflex in rabbits and other mammals, its threshold, prolonged contraction capacity, and its influence on middle ear sound transmission may be related to its demonstrated extensive synaptic field in the reflex chain, particularly in the area of the superior olive, while its many other physiological functions may be made possible by the number, location, and multi-dimensional orientation of its motoneurons and dendrites.

In previous studies of middle ear muscles, the classification of fibre types by histochemical methods was particularly difficult in the bovine and porcine tensor tympani muscle, suggesting the presence of immature fibres. We therefore reexamined the tensor tympani from pigs and cattle of various ages immunohistochemically, using a panel of antimyosin antibodies, including one (anti-NE) specific for neonatal and embryonic myosins. Fibres positive to anti-NE were found in tensor tympani in both species in all ages examined; only a few of these fibres reacted exclusively with this antibody; some also contained slow myosin and the majority also contained adult fast (type IIA) myosin. Furthermore, although the remaining fibres included some of the classical types I and IIA, the majority of them showed a mismatch between their histochemical and immunohistochemical profiles. The morphological appearance of the muscle, the widespread presence of neonatal myosin (often together with another myosin in the same fibre) and the persistence of this composition from birth to adulthood, could be explained by an incomplete development of the muscle fibres, resulting in a 'muscle' much better suited to the role of a ligament.

An accurate description of the functioning Eustachian tube (ET) requires a thorough knowledge of the anatomic relationships of its components. To this end, 15 "normal" adult ETs were obtained, sectioned, and stained with hemotoxylin-eosin. Descriptive and quantitative data of ET structures and their relationships were obtained. Eustachian tube length was normalized and comparisons between specimens made. This analysis suggests (1) in its midsection the cartilage is loosely attached to the cranial base; (2) the deep portion of the tensor veli palatini (TVP) originates from the lateral lamina and the fibrous portion of the lateral membraneous wall; and (3) the levator veli palatini (LVP) can interact with the ET primarily via the elongated medial lamina in the anterior portion of the ET. These observations suggest the ET is opened by a medial rotation of cartilage effected primarily by the TVP, but aided anteriorly by the LVP.

On the basis of functional questions, graphic three-dimensional reconstructions of the tympanic bulla of the rat were made to gain insight into the spatial organisation of the contents of the bulla and especially of the tympanic membrane--ossicular chain--middle ear muscle complex. For this purpose drawings of microscopical sections of complete bullae were fed into the computer to make three-dimensional graphic reconstructions with hidden line removal. From these reconstructions plastic representations were made by the medical artist. The topographical anatomy of the tympanic bulla is discussed in detail and compared to the anatomy of the middle ear in man. It is postulated that, despite differences in spatial organisation of the middle ear of the rat compared to that of man, the middle ear muscles influence the ossicular chain in a comparable way. On the basis of the topographical anatomy it is feasible that the muscles in the rat act synergistically in increasing the stiffness of the ossicular chain.

Serial 10-micron cryostat cross-sections of the tensor tympani muscle and of the medial gastrocnemius muscle from adult domestic cats were incubated for myofibrillar ATPase, NADH tetrazolium reductase (NADH-TR), succinic dehydrogenase (SDH), malate dehydrogenase (MDH) and menadione-linked alpha-glycerophosphate dehydrogenase (alpha GPDH). The optical density of individual tensor tympani and gastrocnemius muscle fibres after different incubation procedures was measured photometrically. The absorbance values of the tensor tympani fibres were related to the values of the type I, type IIA and type IIB fibres of the gastrocnemius muscle. Only two different types of fibre could be demonstrated in the tensor tympani, one type resembling the type I and another resembling the type IIA of the gastrocnemius muscle. The findings are discussed in relation to other, recent immunohistochemical studies on cat tensor tympani muscle fibres.

It is the purpose of this study to attempt a correlation of function, by electromyographic means, of the tensor tympani and tensor veli palatini muscles in humans. Despite the small number of patients tested, it is believed that the similarities and characteristics of the two are unmistakably equivalent. A separate theory for the combined tensor function is discussed in distinction to the stapedius mediated acoustic reflex. The concept of a single tensor muscle, with two anatomic divisions, a common nerve supply, and parallel function, is therefore submitted.

The author has for 25 years manually probed the malleus handle for indications of middle ear pathology. Dissection of the bony auditory tube (BAT) and isthmus comprised 120 fresh autopsy and 26 anatomically prepared temporal bones. The semicanal lamina was not completely ossified in all infants and children and 52% of adults. The tensor tympani muscle was edematous and prolapsed into the superior portion of the BAT in eight ears with otitis media with effusion. Infants and children have the tendon of the tensor tympani muscle inserting into the neck of the malleus at an angle of 60 degrees or greater, possibly explaining the relatively large muscle bulk. It is suggested from these autopsy findings that the BAT and isthmus lumen is a functional 2-way channel for air superiorly and mucus streaming inferiorly. Manual palpation of the cartilaginous auditory tube in infants did not suggest malacia.

Why do two muscles occur in the middle ear of most mammals? In this article selected explanations as to why two muscles occur are critically evaluated. It is argued that these explanations are not compelling. Data are then reviewed that indicate that the tensor tympani has no function to fulfil in the normal operation of the middle ear.

Electromyographic recordings of the activity of the tensor veli palatini, tensor tympani, and stapedius muscles were obtained from several adult human subjects. Muscle responses were recorded under four stimulus conditions, ie, contralateral intense wide-band noise, air jet to the eye, swallow, and electrical stimulation of the tongue. The results indicated that the two tensor muscles responded to the same stimuli in similar patterns. The latter muscle differed from the response of the stapedius.

Estimated are: 1. The axis of the internal acoustic meatus to the horizontal plane in adults and postnatal changes. 2. Eight coronal sections of the temporal bone have been selected to localize the canal systems and structures in the petrous part of the temporal bone and their variations. 3. Described are the different parts of the facial canal, the carotic canal, the auditive tube, the tensor tympani muscle, the major petrosal nerve, and its distances to the carotic canal, the cochlea, the internal acoustic meatus, the supra- and infracochlear cells, the fenestra vestibuli, the fossa jugularis, the canaliculus cochleae, the vestibulum and the semicircular canals. This report includes the development of the supravestibular and other mastoideal cells in the neighbourhood of the canal systems of the petrous bone and the vestibular aqueduct and sac. Estimated are also the distances between the different canal systems. 4. The investigations are discussed with our earlier researches and the results of other researchers and its diagnostic in clinical importance.

Middle ears (515) from 26 species of the rodent family Heteromyidae - genera Dipodomys, Microdipodops, Perognathus, and Liomys - were studied both grossly and histologically, for qualitative and quantitative comparisons. Middle ear modifications characteristic of each genus are qualitatively described. Quantitative comparisons are made among the 26 species in the study. Some correlations between middle ear size and other measurements are discussed. The middle ear is an acoustical transformer that for best efficiency must match the impedance of the cochlea to the impedance of the air in the external auditory meatus. It accomplishes this by a pressure increase and a velocity decrease through the combined effects of the lever and areal ratios; however, because the important consideration is a matching of two impedances rather than an absolute pressure increase, the pressure transformer ratio is a less informative measure of the middle ear's efficiency than is the impedance transform ratio. The impedance transformer mechanism is explained (from a morphological point of view), and equations are presented. Dipodomys, Microdipodops, and Perognathus have a theoretical transmission (at the resonant frequency) of 94-100% of the incident acoustical energy; Liomys, 78-80%. The areal ratio of stapes footplate to 2/3 tympanic membrane is remarkably constant among the species, varying only from 0.04 to 0.07: in Dipodomys and Microdipodops this small ratio is due to the very large tympanic membrane; in Perognathus and Liomys it is due to the extremely small stapes footplate. The lever ratio of incus to malleus varies from 0.28 to 0.33 in Dipodpmys and Microdipodops, from 0.37 to 0.46 in Perognathus, and from 0.55 to 0.60 in Liomys. In addition, the middle ear volumes and the morphology of tympanic membrane, ossicles, ligaments, and muscles, all combine to minimize both mass and stiffness. All these data suggest middle ear mechanisms which are very efficient over a broad frequency range. The middle ear modifications found in heteromyids are adaptive in predator avoidance, especially in areas of little natural cover; nevertheless, contrary to expectations, there is no firm relationship between habitat and the extent of these modifications in the 26 species. However, environment did apparently plan an important role in the evolution of the family, and this is discussed.

Hypothyroidism was induced in guinea pigs by various methods. Using a new technique, electrodes were permanently implanted and action potentials aroused by different sound stimuli recorded and measured. The results obtained before and during the hypometabolic state were analysed and compared with those obtained after replacement therapy. A tentative attempt was made to extrapolate the changes in pattern and magnitude of the action potentials caused by the experimentally induced hypothyroidism, to the hearing disorders observed in patients with thyroid deficiency.

A volumetric study on the tympanic isthmus and its relationship to temporal bone pneumatization was conducted in 110 serially sectioned temporal bones with and without middle ear pathology. With a microcomputer and digitizing tablet, the area of the tympanic isthmus and the degree of pneumatization in sample sections were calculated. Nonpathologic temporal bones showed a significant correlation between the volume of the tympanic isthmus and the degree of pneumatization. The narrowest area of the tympanic isthmus and the degree of pneumatization were also highly correlated. The result indicated a definite inhibition of pneumatization due to chronic middle ear infection when compared with nonpathologic temporal bones.

A brief illustrated atlas demonstrates the progressive relationships of the anatomical structures of the cat's middle ear as one dissects these from the attic approach. There was an attempt to demonstrate the nerves of the lateral semicircular canal and the utricle but without preserving the footplate of the stapes to afford an unobstructed view of the nerves. For the first time, the anatomical features of the cat's middle are are brought together in a progressively illustrated and single source.

Using quantitative histochemical techniques, it was determined that the tensor tympani muscle of the cat consists of three muscle fiber types: type 1, type 2A (staining characteristics similar to the type 1 and type 2A muscle fibers found in the control tibialis anterior muscles), and a third unclassified fiber type (type 3) similar to the 2A fiber type except that it had extremely dense alkaline actomyosin adenosine triphosphatase staining (mean transmittance, type 2A = 33.6%; type 3 = 17.3%), as well as dense staining for periodic acid-Schiff, menadione-linked alpha-glycerolphosphate dehydrogenase, nicotinamide-adenine dinucleotide tetrazolium reductase, and succinic dehydrogenase. The type 1 fiber population was smaller in diameter (mean +/- SD, 14 +/- 4 microns) than the type 2A fiber (mean +/- SD, 21 +/- 5 microns) and the type 3 fiber (mean +/- SD, 22 +/- 6 microns) populations. In all muscles, intrafascicular and extrafascicular fat accumulations were found, with the majority being extrafascicular. Calculations indicate that the tendon occupies approximately 41% of the total muscle volume, while the muscle fibers constitute 59% of the volume.

The clinically important anatomy and morphology of the facial nerve is reviewed. The nuclei, and the supranuclear and internuclear connections are described, and the facial canal, its dehiscences and its relation with the nerve are discussed in detail.

The gross anatomy, microscopical anatomy, morphometry, enzyme histochemistry, immunohistochemistry and electron microscopy of the tensor tympani muscle of the rat was studied. The aim of the study was to create an integrated insight into the morphology of the muscle and to discuss functional implications. The tensor tympani muscle of the rat is an atypical muscle. It is a small muscle composed of very small muscle fibres with a complex microscopical and submicroscopical architecture. Histochemically the muscle consists mainly of fast oxidative glycolytic fibres, but discrepancies are found when anti-heavy chain myosin antibodies are used for fibre typing. Different adult heavy chain myosin isotypes coexist in one single muscle fibre. The electron microscopical study shows that bundles of myofilaments branch and interconnect with other bundles of myofilaments. The findings suggest that the muscle is able to contract fast and is fatigue-resistant. Both features seem to suggest that the muscle has a function in protecting the inner ear against noise damage.

The relationships among the paratubal muscles were studied in human fetal and adult Eustachian tubes. That which has, in recent years, been labeled the tensor veli palatini muscle actually consists of two distinct groups of muscle fibers: a medial group, henceforth termed dilatator tubae, and a lateral group, called tensor veli palatini. The latter was found to have no Eustachian tube origin, but was continuous superiorly with the tensor tympani muscle. The dilatator tubae muscle was found to have a tubal attachment. The participation of this muscle system in the normal functioning of the Eustachian tube-middle ear system in man, and the problems inherent in the development of animal models simulating the physiology of the physiology of the human system, are discussed.

1. The muscle fibres of the tensor tympani and stapedius of the cat have been examined in the light microscope in teased preparations after cholinesterase staining and in the electron microscope.2. In both muscles, two kinds of fibre have been found: those with an individual end-plate and those with multiple nerve terminals.3. The stapedius fibres with an end-plate have fibrils regularly separated from each other by sarcoplasmic reticulum, a straight Z line, transverse tubular T system elements regularly occurring at the junction of A and I bands, an M line, an extensive sole plate area, and numerous post-junctional sarcolemmal infoldings under the nerve terminal. This type of muscle fibre in the tensor tympani has all of these features except that the fibrils are not well separated from each other, T system elements are absent in some sarcomeres, and a typical M line is absent.4. Compared to the individually innervated fibres, the fibres with multiple endings have fibrils poorly separated from each other by sarcoplasmic reticulum, a jagged Z line, very few T system elements, a less extensive sole plate area, and essentially no folds under the nerve terminal. These fibres in both muscles have M lines.5. Muscle fibres have thus been found in both the tensor tympani and stapedius of the cat which conform in their innervation, the structure of their motor nerve endings, and their internal structure to many of the morphological characteristics which are exhibited by slow muscle fibres elsewhere.