Supraorbital ridge and masticatory apparatus II: Humans (Eskimos)

Thirteen adult male skulls of St. Lawrence Island Eskimos were studied to determine the factor or factors responsible for the development of the supraorbital ridges. Results showed that the determining factor is the ratio of the power arm to the load arm of the mandible. The smaller this ratio, the greater the traction force exerted by the anterior temporalis muscle and the greater the supraorbital ridge. Pearson’s correlation coefficient shows two positive correlations, i.e. between the anterior temporalis muscle and the ridge and between the ridge/sinus and the anterior/whole temporalis muscle. Conversely, there is a negative correlation between the power/load arm and the muscle ratio as well as between the power/load arm ratio and the ridge/sinus ratio.     

The mammalian postorbital bar as a torsion-resisting helical strut

The mammalian skull is asymmetrically loaded during mastication because most of these animals chew on only one side at a time. This loading regime tends to twist the braincase relative to the rostral, tooth bearing part of the skull at the zone of potential weakness between the orbits. This torsional effect is exaggerated, and a postorbital bar is present, in those animals with very large masseter and pterygoid muscles. The lines of action of these muscles are oriented at large angles to the long axis of the skull in lateral view, providing large components of force that twist the skull segments relative to one another. When the temporalis is the dominant muscle, the torsional effect is usually less important, and the bar is absent, because this muscle acts at a smaller angle to the skull axis. The postorbital bar exhibits the predicted three dimensional spatial orientation required to resist torsional forces: it is a segment of an imaginary 45° helix that is wound around the skull, if the skull is idealized as a cylinder. This orientation is significant because, in general, maximum compressive and tensile shear stresses lie along 45° helices on a cylinder loaded in torsion; to resist torsion, material should be placed far from the axis of torsion and along a helix oriented at 45° to the deforming forces. Each half of a supraorbital ridge is also a segment of a 45° helix that is perpendicular to the helix passing through the postorbital bar. This model suggests that the postorbital bar is loaded in compression on the chewing side and in tension on the non-chewing side; the supraorbital ridge is loaded in tension on the chewing side and in compression on the non-chewing side.     

Predicted pattern of human muscle activity during clenching derived from a computer assisted model: symmetric vertical bite forces

A computer assisted three-dimensional model of the jaw, based on linear programming, is presented. The upper and lower attachments of the muscles of mastication have been measured on a single human skull and divided into thirteen independent units on each side--a total of 26 muscle elements. The direction (in three dimensions) and maximum forces that could be developed by each muscle element, the bite reaction and two joint reactions are included in the model. It is shown for symmetrical biting that a model which minimizes the sum of the muscle forces used to produce a given bite force activates muscles in a way which corresponds well with previous observations on human subjects. A model which minimizes the joint reactions behaves differently and is rejected. An analysis of the way the chosen model operates suggests that there are two types of jaw muscles, power muscles and control muscles. Power muscles (superficial masseter, medial pterygoid and some of temporalis) produce the bite force but tend to displace the condyle up or down the articular eminence. This displacement is prevented by control muscles (oblique temporalis and lateral pterygoid) which have very poor moment arms for generating usual bite forces, but are efficient for preventing condylar slide. The model incorporates the concept that muscles consist of elements which can contract independently. It predicts that those muscle elements with longer moment arms relative to the joint are the first to be activated and, as the bite force increases, a ripple of activity spreads into elements with shorter moment arms. In general, the model can be used to study the three-dimensional activity in any system of joints and muscles.     

Temporalis function in anthropoids and strepsirrhines: an EMG study

The major purpose of this study is to analyze anterior and posterior temporalis muscle force recruitment and firing patterns in various anthropoid and strepsirrhine primates. There are two specific goals for this project. First, we test the hypothesis that in addition to transversely directed muscle force, the evolution of symphyseal fusion in primates may also be linked to vertically directed balancing-side muscle force during chewing (Hylander et al. [2000] Am. J. Phys. Anthropol. 112:469-492). Second, we test the hypothesis of whether strepsirrhines retain the hypothesized primitive mammalian condition for the firing of the anterior temporalis, whereas anthropoids have the derived condition (Weijs [1994] Biomechanics of Feeding in Vertebrates; Berlin: Springer-Verlag, p. 282-320). Electromyographic (EMG) activities of the left and right anterior and posterior temporalis muscles were recorded and analyzed in baboons, macaques, owl monkeys, thick-tailed galagos, and ring-tailed lemurs. In addition, as we used the working-side superficial masseter as a reference muscle, we also recorded and analyzed EMG activity of the left and right superficial masseter in these primates. The data for the anterior temporalis provided no support for the hypothesis that symphyseal fusion in primates is linked to vertically directed jaw muscle forces during mastication. Thus, symphyseal fusion in primates is most likely mainly linked to the timing and recruitment of transversely directed forces from the balancing-side deep masseter (Hylander et al. [2000] Am. J. Phys. Anthropol. 112:469-492). In addition, our data demonstrate that the firing patterns for the working- and balancing-side anterior temporalis muscles are near identical in both strepsirrhines and anthropoids. Their working- and balancing-side anterior temporalis muscles fire asynchronously and reach peak activity during the power stroke. Similarly, their working- and balancing-side posterior temporalis muscles also fire asynchronously and reach peak activity during the power stroke. Compared to these strepsirrhines, however, the balancing-side posterior temporalis of anthropoids appears to have a relatively delayed firing pattern. Moreover, based on their smaller W/B ratios, anthropoids demonstrate a relative increase in muscle-force recruitment of the balancing-side posterior temporalis. This in turn suggests that anthropoids may emphasize the duration and magnitude of the power stroke during mastication. This hypothesis, however, requires additional testing. Furthermore, during the latter portion of the power stroke, the late activity of the balancing-side posterior temporalis of anthropoids apparently assists the balancing-side deep masseter in driving the working-side molars through the terminal portion of occlusion.     

Structure and direction of jaw adductor muscles as herbivorous adaptations in <Emphasis Type="Italic">Neotoma mexicana</Emphasis> (Muridae,Rodentia)

The herbivorous adaptations of the jaw adductor muscles in Neotoma mexicana were clarified by a comparative study with an unspecialized relative, Peromyscus maniculatus. In P. maniculatus, the anterior part of the deep masseter arises entirely from the lateral side of an aponeurosis, i.e., superior zygomatic plate aponeurosis, whereas N. mexicana has an additional aponeurosis for this part of the muscle, and the fibers attach on both sides of the superior zygomatic plate aponeurosis. Although the structure of the temporalis muscle is nearly identical in the two genera, a clear aponeurosis of origin occurs only in N. mexicana. These characteristics allow fibrous tissues to be processed with a large occlusal force. The deep masseter, internal pterygoid, and external pterygoid muscles of N. mexicana incline more anterodorsally than those of P. maniculatus. The transverse force component of these muscles relative to whole muscle force is smaller in N. mexicana than in P. maniculatus, with the exception of the internal pterygoid. The anterior part of the temporalis muscle of N. mexicana is specialized to produce occlusal pressure. These findings suggest that in N. mexicana a large anterior force is required to move the heavy mandible, due to the hypsodont molars, against frictional force from food, and that the posterior pull of the temporalis, which adjusts the forward force by the other jaw adductor muscles to a suitable level, need not be large for the mandibular movement.     

The blood supply of the reverse temporalis muscle flap: anatomic study and clinical implications

Although the reverse temporalis muscle flap has been used clinically, the exact vascular connection between the superficial and deep temporal vessels has not been clearly defined. The purpose of this study was to investigate the vascular territory of the reverse temporalis muscle supplied by the superficial temporal vessels. Six cadaver heads were studied using a colored lead oxide injection through the superficial temporal artery. The specimens were examined macroscopically and radiographically. The reverse temporalis muscle flap was then applied to a clinical case presenting with traumatic anterior skull base defect communicating with the nasal cavity. The cadaver specimens demonstrated that the superficial temporal artery formed an average 1.3 +/- 0.2 cm in width of dense vascular zone, which was located within 1.8 cm below the superior temporal line. The dense vascular network further perfused the anterior and posterior deep temporal arteries and the muscular branch of the middle temporal artery to supply the temporalis muscle. The mean perfused area of the temporalis muscle was 83 percent, ranging from 79 to 89 percent, in five cadaver heads. One cadaver revealed only 55 percent of perfused area in the absence of the muscular branch of the middle temporal artery. The consistent area without perfusion was located in the distal third of the posterior portion of the reverse temporalis muscle. In clinical cases, the reverse temporalis muscle flap was used successfully to obliterate the anterior skull base defect without evidence of muscle flap necrosis. The exact blood supply to the distal third of the posterior portion of the reverse temporalis muscle flap needs to be investigated further in vivo. Particular attention was paid to the inclusion of the muscular branch of the middle temporal artery in this flap to augment the blood supply to the temporalis muscle.     

Strain in the braincase and its sutures during function

The skull is distinguished from other parts of the skeleton by its composite construction. The sutures between bony elements provide for interstitial growth of the cranium, but at the same time they alter the transmission of stress and strain through the skull. Strain gages were bonded to the frontal and parietal bones of miniature pigs and across the interfrontal, interparietal and coronal sutures. Strains were recorded 1) during natural mastication in conjunction with electromyographic activity from the jaw muscles and 2) during stimulation of various cranial muscles in anesthetized animals. Vault sutures exhibited vastly higher strains than did the adjoining bones. Further, bone strain primarily reflected torsion of the braincase set up by asymmetrical muscle contraction; the tensile axis alternated between +45 degrees and -45 degrees depending on which diagonal masseter/temporalis pair was most active. However, suture strains were not related to overall torsion but instead were responses to local muscle actions. Only the coronal suture showed significant strain (tension) during jaw opening; this was caused by the contraction of neck muscles. All sutures showed strain during jaw closing, but polarity depended on the pattern of muscle usage. For example, masseter contraction tensed the coronal suture and the anterior part of the interfrontal suture, whereas the temporalis caused compression in these locations. Peak tensile strains were larger than peak compressive strains. Histology suggested that the skull is bent at the sutures, with the ectocranial surface tensed and the endocranial surface predominantly compressed. Collectively, these results indicate that skulls with patent sutures should be analyzed as complexes of independent parts rather than solid structures.     

Three-dimensional temporomandibular joint muscle attachment morphometry and its impacts on musculoskeletal modeling

In musculoskeletal models of the human temporomandibular joint (TMJ), muscles are typically represented by force vectors that connect approximate muscle origin and insertion centroids (centroid-to-centroid force vectors). This simplification assumes equivalent moment arms and muscle lengths for all fibers within a muscle even with complex geometry and may result in inaccurate estimations of muscle force and joint loading. The objectives of this study were to quantify the three-dimensional (3D) human TMJ muscle attachment morphometry and examine its impact on TMJ mechanics. 3D muscle attachment surfaces of temporalis, masseter, lateral pterygoid, and medial pterygoid muscles of human cadaveric heads were generated by co-registering measured attachment boundaries with underlying skull models created from cone-beam computerized tomography (CBCT) images. A bounding box technique was used to quantify 3D muscle attachment size, shape, location, and orientation. Musculoskeletal models of the mandible were then developed and validated to assess the impact of 3D muscle attachment morphometry on joint loading during jaw maximal open-close. The 3D morphometry revealed that muscle lengths and moment arms of temporalis and masseter muscles varied substantially among muscle fibers. The values calculated from the centroid-to-centroid model were significantly different from those calculated using the ‘Distributed model’, which considered crucial 3D muscle attachment morphometry. Consequently, joint loading was underestimated by more than 50% in the centroid-to-centroid model. Therefore, it is necessary to consider 3D muscle attachment morphometry, especially for muscles with broad attachments, in TMJ musculoskeletal models to precisely quantify the joint mechanical environment critical for understanding TMJ function and mechanobiology.     

Mutual influences of upper and lower extrimities during cyclic movements

The possibility of muscle activation of passive arm during its cyclic movements, imposed by active movements of contralateral arm or by experimenter was studied, as well as the influence of lower extremities cyclic movements onto arm muscles activity. In addition to that the activity of legs muscles was estimated in dependence on motor task condition for arms. Ten healthy supine subjects carried out opposite movements of arms with and without stepping-like movements of both legs. The experiment included three conditions for arm movements: 1) the active movements of both arms; 2) the active movements of one arm, when other entirely passive arm participated in the movement by force; 3) passive arm movement caused by experimenter. In the condition 2) additional load on active arm was applied (30 N and 60 N). In all three conditions the experiment was carried out with arms movements only or together with legs movements. The capability of passive moving arm muscles activation depended on increasing afferent inflow from muscles of contralateral arm was demonstrated. Emerging electrical activity was modulated in the arms movements cycle and depended on the degree of active arm loading. During combined active movements of arms and legs the reduction of activity in the flexor muscles of shoulder and forearm was observed. Concomitant arms movements increased the magnitude ofelectromiographic bursts during passive stepping-like movements in the most of recorded muscles, and the same increasing was only observed in biceps femoris and tibialis anterior muscles during active legs movement. The increasing of loading of one arm caused essential augmentation of EMG-activity in the majority of recording legs muscles. The data obtained are the additional proof of existence of functionally significant neuronal interaction both between arms and between upper and lower extremities, which is evidently depend on the intraspinal neuronal connections.     

Three-dimensional model to predict muscle forces and their relation to motor variances in reaching arm movements

A three-dimensional (3-D) arm movement model is presented to simulate kinematic properties and muscle forces in reaching arm movements. Healthy subjects performed reaching movements repetitively either with or without a load in the hand. Joint coordinates were measured. Muscle moment arms, 3-D angular acceleration, and moment of inertias of arm segments were calculated to determine 3-D joint torques. Variances of hand position, arm configuration, and muscle activities were calculated. Ratios of movement variances observed in the two conditions (load versus without load) showed no differences for hand position and arm configuration variances. Virtual muscle force variances for all muscles except deltoid posterior and EMG variances for four muscles increased significantly by moving with the load. The greatly increased variances in muscle activity did not imply equally high increments in kinematic variances. We conclude that enhanced muscle cooperation through synergies helps to stabilize movement at the kinematic level when a load is added.     

The functional relationship between feeding type and jaw and cranial morphology in ungulates

The relationship between jaw and skull morphology and feeding type (grazer, mixed feeder, browser, frugivorous, omnivorous) was analysed in 94 species of extant ungulates. A total of 21 morphological traits of the jaw and skull (17 and 4, respectively) were analysed using analysis of covariance, with body mass as covariate. To take into account the phylogenetic effect, simulations were generated under the Brownian motion model of character evolution. Analysis of covariance was applied to these simulations and the simulated F-ratios were used to assess the signification of the F-ratios for the real values of the traits. The feeding types had a weak effect on ungulate cranial and jaw morphology in comparison with the phylogenetic effect, since, before phylogeny correction, the analysis of covariance showed statistically significant differences associated with feeding type in 15 out of the 21 traits analysed. After controlling for phylogeny, only 2 significant traits remained, the length of the coronoid process and the occipital height. Omnivorous species had shorter coronoid processes than grazers or mixed feeders, and the occipital height was greater in the omnivorous species than in the grazers, mixed feeders or browsers. The coronoid process is involved in the generation of bite force, being the effective moment arm of the temporalis muscle, and occipital height is positively related to the force exerted by the temporalis muscle. This result matches the hypothesis that species with a toughness diet should show higher bite force (“toughness” describes the resistance of a material to being mechanically broken down). When the omnivorous species were excluded from the analysis, no differences in jaw and skull morphology were detected between the rest of the feeding types. Received: 1 September 1998 / Accepted: 2 November 1998     

Biomechanics of the masticatory apparatus of Pteropus giganteus (Megachiroptera)

Jaw mechanics in Pteropus were studied by means of a three-dimensional model. The model included several parameters of muscle architecture, combined with quantified movement and electromyographical data. Estimates of the nature of the applied forces that act upon the mandible during a chewing cycle, and subsequent estimates of reaction forces at the bite point and joints during the powerstroke, were thus obtained for different food consistencies. The resultant muscle force (relative to the palate) shifts from upward and slightly backward at large gapes to upward and markedly backward at the end of closing. The resultant simultaneously moves anteriorly. During the powerstroke it retains a constant position and orientation along the thickened anterior edge of the coronoid process. The early stages of opening are guided by the slope of the teeth and mandibular fossa; during the remaining part of opening the working line of the resultant crosses the skull behind the joint and thus acquires an opening moment. The bite force has downward and forward components, and a slight transverse component. For a given applied muscular force its magnitude is larger in more posteriorly positioned bite points. Both joints are loaded, the contralateral one more than the ipsilateral. Food consistency affects magnitude and orientation of the applied force, and hence, magnitude and orientation of the bite force and magnitude of the joint reaction forces. The magnitude of masseter activity relative to temporalis activity appears to be the key factor for the orientation of the bite force, and hence for the mechanical optimal position of the food. The adaptive value of the general topography of the masticatory muscles in Pteropus is discussed.     

Electromyography of the anterior temporalis and masseter muscles of owl monkeys (Aotus trivirgatus) and the function of the postorbital septum

Anthropoids and tarsiers are distinguished from all other vertebrates by the possession of a postorbital septum, which is formed by the frontal, alisphenoid, and zygomatic bones. Cartmill [(1980) In: Evolutionary Biology of the New World Monkeys and Continental Drift. New York: Plenum, p 243-274] suggested that the postorbital septum evolved in the stem lineage of tarsiers and anthropoids to insulate the eye from movements arising in the temporal fossa. Ross [(1996) Am J Phys Anthropol 91:305-324] suggested that the septum insulates the orbital contents from incursions by the line of action of the anterior temporal muscles caused by the unique combination of high degrees of orbital frontation and convergence. Both of these hypotheses must explain why insulation of the orbital contents could not be achieved by decreasing the size of the anterior temporal musculature with a corresponding increase in size of the remaining jaw adductors, rather than evolving a postorbital septum. One possibility is that the anterior temporalis is an important contributor to vertically directed bite forces during all biting and chewing activities. Another possibility is that reduction in anterior temporal musculature would compromise the ability to produce powerful bite forces, either at the incisors or along the postcanine toothrow. To evaluate these hypotheses, electromyographic (EMG) recordings were made from the masseter muscle and the anterior and posterior portions of the temporalis muscles of two owl monkeys, Aotus trivirgatus. The EMG data indicate that anterior temporalis activity relative to that of the superficial masseter is lower during incision than mastication. In addition, activity of the anterior temporalis is not consistently higher than the posterior temporalis during incision. The data indicate relatively greater activity of anterior temporalis compared to other muscles during isometric biting on the postcanine toothrow. This may be due to decreased activity in superficial masseter and posterior temporalis, rather than elevated anterior temporalis activity. The anterior temporalis is not consistently less variable in activity than the superficial masseter and posterior temporalis. The EMG data gathered here indicate no reason for suggesting that the anterior temporal muscles in anthropoids are utilized especially for incisal preparation of hard fruits. Maintenance of relatively high EMG activity in anterior temporalis across a wide range of biting behaviors is to be expected in a vertically oriented and rostrally positioned muscle such as this because, compared to the posterior temporalis, superficial masseter and medial pterygoid, it can contribute relatively larger vertical components of force to bites along the postcanine toothrow. The in vivo data do not support this hypothesis, possibly because of effects of bite point and bite force orientation.     

Functional assessment of subfamily variation in maxillomandibular morphology among Old World monkeys

Among Old World monkeys, subfamily variation in maxillomandibular form is commonly attributed to divergent dietary and social behaviors. However, our knowledge of any musculoskeletal adaptations for gape in cercopithecines, and folivory in colobines, is incomplete. Such data are requisite to a more informed perspective on the evolutionary morphology of these taxa. Structural analyses of gape and biomechanical efficiency were applied to a representative sample of adult cercopithecids. Factors pertaining to the biomechanical scaling of cranial structures were evaluated with least-squares bivariate regression techniques. To assess subfamily differences in masticatory efficiency, analyses of covariance were made between relevant factors. Cercopithecines achieve increased gape and relative canine size mainly with strong positive allometry of the facial skull, combined with a larger gonial angle. Colobines possess a relatively long masseter lever arm and short facial skull, as well as an enlargened masseter-medial pterygoid complex. Subfamily differences in temporalis lever arm scaling are negligible. Biomechanical comparisons within and between subfamilies suggest that the mechanical advantage of the temporalis is relatively greater than that of the masseter, while the mechanical advantage of both muscles increases with face length. Evidence is presented to stress the need for adequate consideration of the dependent variable in allometric investigations of skull form.     

In vivo measurement-based estimations of the moment arm in the human tibialis anterior muscle-tendon unit

The aim of this study was to estimate the moment arm of human tibialis anterior (TA) muscle-tendon unit at rest and during isometric dorsiflexion maximum voluntary contraction (MVC) from in vivo sagittal-plane magnetic resonance (MR) and ultrasound scans. Two methods were employed, both of them based on the assumption that the ankle joint complex and TA muscle-tendon unit operate in the sagittal plane. Using method A, moment arms were obtained from MR scans of the foot by measuring the perpendicular distance between a moving centre of rotation in the talo-crural joint and the TA tendon action line. Using method B, moment arms were calculated from the ratio of TA tendon displacement, which was estimated from a planimetric muscle model using pennation angles and muscle thickness measured by ultrasonography, to the tibial rotation around the talus, which was measured from the foot MR scans. Using either of the two methods at rest, the estimated TA moment arm decreased from approximately 4.5 to approximately 2.9 cm in the transition from dorsiflexion to plantarflexion. Using method A, moment arms during MVC were larger by 0.9-1.5 cm (33-44%, P < 0.01) than the respective resting estimations. In contrast, no difference (P > 0.05) was found between the resting and MVC moment arm estimations of method B. Limitations in the oversimplified musculoskeletal model used raise questions for the validity of both method estimations.     

Masticatory Muscle Anatomy and Feeding Efficiency of the American Beaver, <Emphasis Type="Italic">Castor canadensis</Emphasis> (Rodentia,Castoridae)

Beavers are well-known for their ability to fell large trees through gnawing. Yet, despite this impressive behavior, little information exists on their masticatory musculature or the biomechanics of their jaw movements. It was hypothesized that beavers would have a highly efficient arrangement of the masticatory apparatus, and that gnawing efficiency would be maintained at large gape. The head of an American beaver, Castor canadensis, was dissected to reveal the masticatory musculature. Muscle origins and insertions were noted, the muscles were weighed and fiber lengths measured. Physiological cross-sectional areas were determined, and along with the muscle vectors, were used to calculate the length of the muscle moment arms, the maximum incisor bite force, and the proportion of the bite force projected along the long axis of the lower incisor, at occlusion and 30° gape. Compared to other sciuromorph rodents, the American beaver was found to have large superficial masseter and temporalis muscles, but a relatively smaller anterior deep masseter. The incisor bite force calculated for the beaver (550–740 N) was much higher than would be predicted from body mass or incisor dimensions. This is not a result of the mechanical advantage of the muscles, which is lower than most other sciuromorphs, but is likely related to the very high percentage (>96 %) of bite force directed along the lower incisor long axis. The morphology of the skull, mandible and jaw-closing muscles enable the beaver to produce a very effective and efficient bite, which has permitted beavers to become highly successful ecosystem engineers.     

Dry versus wet and gross: Comparisons between the dry skull method and gross dissection in estimations of jaw muscle cross-sectional area and bite forces in sea otters

Bite force is a measure of feeding performance used to elucidate links between animal morphology, ecology, and fitness. Obtaining live individuals for in vivo bite-force measurements or freshly deceased specimens for bite force modeling is challenging for many species. Thomason's dry skull method for mammals relies solely on osteological specimens and, therefore, presents an advantageous approach that enables researchers to estimate and compare bite forces across extant and even extinct species. However, how accurately the dry skull method estimates physiological cross-sectional area (PCSA) of the jaw adductor muscles and theoretical bite force has rarely been tested. Here, we use an ontogenetic series of southern sea otters (Enhydra lutris nereis) to test the hypothesis that skeletomuscular traits estimated from the dry skull method accurately predicts test traits derived from dissection-based biomechanical modeling. Although variables from these two methods exhibited strong positive relationships across ontogeny, we found that the dry skull method overestimates PCSA of the masseter and underestimates PCSA of the temporalis. Jaw adductor in-levers for both jaw muscles and overall bite force are overestimated. Surprisingly, we reveal that sexual dimorphism in craniomandibular shape affects temporalis PCSA estimations; the dry skull method predicted female temporalis PCSA well but underestimates male temporalis PCSA across ontogeny. These results highlight the importance of accounting for sexual dimorphism and other intraspecific variation when using the dry skull method. Together, we found the dry skull method provides an underestimation of bite force over ontogeny and that the underlying anatomical components driving bite force may be misrepresented.     

Myofascial force transmission between antagonistic rat lower limb muscles: Effects of single muscle or muscle group lengthening

Effects of lengthening of the whole group of anterior crural muscles (tibialis anterior and extensor hallucis longus muscles (TA + EHL) and extensor digitorum longus (EDL)) on myofascial interaction between synergistic EDL and TA + EHL muscles, and on myofascial force transmission between anterior crural and antagonistic peroneal muscles, were investigated. All muscles were either passive or maximally active. Peroneal muscles were kept at a constant muscle tendon complex length. Either EDL or all anterior crural muscles were lengthened so that effects of lengthening of TA + EHL could be analyzed. For both lengthening conditions, a significant difference in proximally and distally measured EDL passive and active forces, indicative of epimuscular myofascial force transmission, was present. However, added lengthening of TA + EHL significantly affected the magnitude of the active and passive load exerted on EDL. For the active condition, the direction of the epimuscular load on EDL was affected; at all muscle lengths a proximally directed load was exerted on EDL, which decreased at higher muscle lengths. Lengthening of anterior crural muscles caused a 26% decrease in peroneal active force.

Extramuscular myofascial connections are thought to be the major contributor to the EDL proximo-distal active force difference. For antagonistic peroneal complex, the added distal lengthening of a synergistic muscle increases the effects of extramuscular myofascial force transmission.     

金丝猴颅骨及牙齿的比较形态研究

金丝猴(Rhinopithecus roxellanae M.-E.)自从1870年订名以来,对它的研究多限于分类和个体生态习性的观察描述,至于它的形态解剖方面的论述国内几无报道。国外Hooizer(1950)和Swindler(1976)对其牙齿作了简单扼要的描述,前者并在11例川金丝猴头骨中发现一例左侧上颌骨具有P⁴。这次我们对金丝猴系统的研究过程中,在解剖方面,除了进行各器官系统解剖外,同时还与猕猴、黑叶猴相比较,并对其器官的形态变化和生态生理机能的结合上给以适当注意和解释。