Jumping mechanisms and performance in beetles. II. Weevils (Coleoptera: Curculionidae: Rhamphini)

We describe the kinematics and performance of the natural jump in the weevil Orchestes fagi (Fabricius, 1801) (Coleoptera: Curculionidae) and its jumping apparatus with underlying anatomy and functional morphology. In weevils, jumping is performed by the hind legs and involves the extension of the hind tibia. The principal structural elements of the jumping apparatus are (1) the femoro-tibial joint, (2) the metafemoral extensor tendon, (3) the extensor ligament, (4) the flexor ligament, (5) the tibial flexor sclerite and (6) the extensor and flexor muscles. The kinematic parameters of the jump (from minimum to maximum) are 530–1965 m s^?2 (acceleration), 0.7–2.0 m s^?1 (velocity), 1.5–3.0 ms (time to take-off), 0.3–4.4 μJ (kinetic energy) and 54–200 (g-force). The specific joint power as calculated for the femoro-tibial joint during the jumping movement is 0.97 W g^?1. The full extension of the hind tibia during the jump was reached within up to 1.8–2.5 ms. The kinematic parameters, the specific joint power and the time for the full extension of the hind tibia suggest that the jump is performed via a catapult mechanism with an input of elastic strain energy. A resilin-bearing elastic extensor ligament that connects the extensor tendon and the tibial base is considered to be the structure that accumulates the elastic strain energy for the jump. According to our functional model, the extensor ligament is loaded by the contraction of the extensor muscle, while the co-contraction of the antagonistic extensor and flexor muscles prevents the early extension of the tibia. This is attributable to the leverage factors of the femoro-tibial joint providing a mechanical advantage for the flexor muscles over the extensor muscles in the fully flexed position. The release of the accumulated energy is performed by the rapid relaxation of the flexor muscles resulting in the fast extension of the hind tibia propelling the body into air.     

The metatibial extensor and flexor tendons in Coleoptera

The metatibiae of genera in several families of Coleoptera with enlarged metafemora are examined, including Chrysomelidae (Alticinae, Galerucinae, Sagrinae), Bruchidae (Pachymerinae, Rhae-binae, Eubaptinae, Bruchinae), Scirtidae and Oedemeridae. There is an evident pattern concerning the relative size of the tibial extensor and flexor tendons that is dependent on the type of hind leg movement of a specific beetle group. Beetle groups that jump (e.g. Alticinae, Scirtidae) always have a greatly enlarged metatibial extensor tendon and associated musculature. However, other groups with swollen metafemora that do not jump have enlarged metatibial flexor tendons with the associated musculature for holding/grasping onto the vegetation (Sagrinae, Bruchidae) or onto the female during copulation (male Oedemera). This indicates a strong functional relationship between Sagrinae and Bruchidae, both with large flexor tendons, and between the Alticinae and Galerucinae, with relatively large extensor tendons; these two cases may also have phylogenetic meaning. This pattern of the metatibial extensor and flexor tendon size related to function is presumably true for at least all other Coleoptera.     

Octopaminergic modulation of locust motor neurones

The effect of octopamine on the fast extensor and the flexor tibiae motor neurones in the locust (Schistocerca gregaria) metathoracic ganglion, and also on synaptic transmission from the fast extensor to the flexor motor neurones, was examined. Bath application or ionophoresis of octopamine depolarized and increased the excitability of the flexor tibiae motor neurones. 1 mM octopamine reduced the amplitude of the fast extensor-evoked EPSP in the slow but not the fast flexor motor neurones, whereas 10 mM octopamine could reduce the EPSP amplitude in both. Octopamine broadened the fast extensor action potential and reduced the amplitude of the afterhyperpolarization, the modulation requiring feedback resulting from movement of the tibia. Octopamine also increased the frequency of synaptic inputs onto the tibial motor neurones, and could cause rhythmic activity in the flexor motor neurones, and reciprocal activity in flexor and extensor motor neurones. Octopamine also increased the frequency of spontaneous spiking in the octopaminergic dorsal unpaired median neurones. Repetitive stimulation of unidentified dorsal unpaired median neurones could mimic some of the effects of octopamine. However, no synaptic connections were found between dorsal unpaired median neurones and the tibial motor neurones. The diverse effects of octopamine support its role in mediating arousal.     

Sensorimotor pathways processing vibratory signals from the femoral chordotonal organ of the stick insect

The femoral chordotonal organ of stick insects senses position and velocity of movements in the femur-tibia joint, as well as tibial vibration. While sensory information about large-scale tibial movements is processed by a well-known neuronal network and elicits resistance reflexes in extensor and flexor tibiae motoneurons, it is not yet known how sensory information about vibration of the tibia is processed. We investigated the transmission of vibration stimuli to tibial extensor motoneurons and their premotor interneurons. Vibration stimuli applied to the femoral chordotonal organ evoked responses in tibial extensor and flexor muscles. During ongoing vibration this response adapted rapidly. This adaptation had no effect on the motoneuronal response to large-scale tibial movements. Recording from premotor interneurons revealed that vibratory signals were processed in part by the same interneuronal pathways as (large-scale) velocity and position information. While only certain parts of the interneuronal reflex pathways showed little or no response during vibration stimuli, most neurons responded to both position or velocity stimuli and vibration at the femoral chordotonal organ. We conclude that sensory information about vibration of the tibia shares part of the interneuronal pathways that transmit sensory information about large-scale tibial movements to the motoneurons. Accepted: 25 April 1999     

Motor patterns during kicking movements in the locust

Locusts (Schistocerca gregaria) use a distinctive motor pattern to extend the tibia of a hind leg rapidly in a kick. The necessary force is generated by an almost isometric contraction of the extensor tibiae muscle restrained by the co-contraction of the flexor tibiae (co-contraction phase) and aided by the mechanics of the femoro-tibial joint. The stored energy is delivered suddenly when the flexor muscle is inhibited. This paper analyses the activity of motor neurons to the major hind leg muscles during kicking, and relates it to tibial movements and the resultant forces.During the co-contraction phase flexor tibiae motor neurons are driven by apparently common sources of synaptic inputs to depolarized plateaus at which they spike. The two excitatory extensor motor neurons are also depolarized by similar patterns of synaptic inputs, but with the slow producing more spikes at higher frequencies than the fast. Trochanteral depressors spike at high frequency, the single levator tarsi at low frequency, and common inhibitors 2 and 3 spike sporadically. Trochanteral levators, depressor tarsi, and a retractor unguis motor neuron are hyperpolarized.Before the tibia extends all flexor motor neurons are hyperpolarized simultaneously, two common inhibitors, and the levator trochanter and depressor tarsi motor neurons are depolarized. Later, but still before the tibial movement starts, the extensor tibiae and levator tarsi motor neurons are hyperpolarized. After the movement has started, the extensor motor neurons are hyperpolarized further and the depressor trochanteris motor neurons are also hyperpolarized, indicating a contribution of both central and sensory feedback pathways.Variations in the duration of the co-contraction of almost twenty-fold, and in the number of spikes in the fast extensor tibiae motor neuron from 2–50 produce a spectrum of tibial extensions ranging from slow and weak, to rapid and powerful. Flexibility in the networks producing the motor pattern therefore results in a range of movements suited to the fluctuating requirements of the animal.     

Local innervation patterns of the metathoracic flexor and extensor tibiae motor neurons in the cricket Gryllus bimaculatus

To elucidate neural mechanisms underlying walking and jumping in insects, motor neurons supplying femoral muscles have been identified mainly in locusts and katydids, but not in crickets. In this study, the motor innervation patterns of the metathoracic flexor and extensor tibiae muscles in the cricket, Gryllus bimaculatus were investigated by differential back-fills and nerve recordings. Whereas the extensor tibiae muscle has an innervation pattern similar to that of other orthopterans, the flexor has an innervation unique to this species. The main body of the flexor muscle is divided into the proximal, middle and distal regions, which receive morphologically unique terminations from almost non-overlapping sets of motor neurons. The proximal region is innervated by about 12 moderate-sized excitatory motor neurons and two inhibitory neurons while the middle and distal regions are innervated by three and four large excitatory motor neurons, respectively. The most-distally located accessory flexor muscle, inserting on a common flexor apodeme with the main muscle, is innervated by at least four small excitatory (slow-type) and two common inhibitory motor neurons. The two excitatory and two inhibitory motor neurons that innervate the accessory flexor muscle also innervate the proximal bundles of the main flexor muscle. This suggests that the most proximal and distal parts of the flexor muscle participate synergistically in fine motor control while the rest participates in powerful drive of tibial flexion movement.     

Adaptive reconfiguration of a reflex circuit during different motor programmes in the locust

The cuticle strain which develops in the hindleg tibiae when a locust prepares to kick, or when the tibia thrusts against an obstacle, is detected by two campaniform sensilla, which reflexly excite the fast extensor tibiae motoneuron, some of the flexor tibiae motoneurons and nonspiking interneurons. The reflex excitation is adaptive for the extensor motoneuron during both co-activation and thrusting, but is only adaptive for the flexor motoneurons during co-activation, and is maladaptive during thrusting. We show that the femoral chordotonal organ, which monitors tibial position, controls the efficacy of the strain feedback. The campaniform sensilla-induced depolarization in the extensor motoneuron is about twice as large when the tendon is in mid position (reflecting a tibial-femoral angle of 90°) than when fully stretched (reflecting tibial flexion), while in the flexors the reverse is true. The amplitudes of excitatory postsynaptic potentials evoked by single campaniform sensilla spikes, are, however, not affected. Our data suggests that the chordotonal organ modulates the gain of the strain feedback onto the motoneurons by exciting interneuronal circuits whose output sums with the former. Thrusting typically occurs with the tibia partially extended, therefore the actions of the chordotonal organ support the production of a maximal thrusting force. Accepted: 27 December 1996     

Effects of load inversion in cockroach walking

To examine how walking patterns are adapted to changes in load, we recorded leg movements and muscle activities when cockroaches (Periplaneta americana) walked upright and on an inverted surface. Animals were videotaped to measure the hindleg femoro-tibial joint angle while myograms were taken from the tibial extensor and flexor muscles. The joint is rapidly flexed during swing and extended in stance in upright and inverted walking. When inverted, however, swing is shorter in duration and the joint traverses a range of angles further in extension. In slow upright walking, slow flexor motoneurons fire during swing and the slow extensor in stance, although a period of co-contraction occurs early in stance. In inverted walking, patterns of muscle activities are altered. Fast flexor motoneurons fire both in the swing phase and early in stance to support the body by pulling the animal toward the substrate. Extensor firing occurs late in stance to propel the animal forward. These findings are discussed within the context of a model in which stance is divided into an early support and subsequent propulsion phase. We also discuss how these changes in use of the hindleg may represent adaptations to the reversal of the effects of gravity.     

Effects of movement speed and joint position on knee flexor torque in healthy and post-surgical subjects

Coactivation of knee flexors during knee extension assists in joint stability by exerting an opposing torque to the anterior tibial displacement induced by the quadriceps. This opposing torque is believed to be generated by eccentric muscle actions that stiffen the knee, thereby attenuating strain to joint ligaments, particularly the anterior cruciate ligament (ACL). However, as the lengths of knee muscles vary with changes in joint position, the magnitude of flexor/extensor muscle force coupling may likewise vary, possibly affecting the capacity for active knee stabilization. The purpose of this study was to assess the effect of changes in movement speed and joint position on eccentric/concentric muscle action relationships in the knees of uninjured (UNI) and post-ACL-surgery (INJ) subjects (n = 14). All subjects were tested for maximum eccentric and concentric torque of the contralateral knee flexors and extensor muscles at four isokinetic speeds (15 degrees-60 degrees x s(-1)) and four joint position intervals (20 degrees-60 degrees of knee flexion). Eccentric flexor torque was normalized to the percentage of concentric flexor torque generated at each joint position interval for each speed tested (flexor E-C ratio). In order to estimate the capacity of the knee flexors to resist active knee extension, the eccentric-flexor/concentric-extensor ratios were also computed for each joint position interval and speed (flexor/extensor E-C ratio). The results revealed that eccentric torque surpassed concentric torque by 3%-144% across movement speeds and joint position intervals. The magnitude of the flexor E-C ratio and flexor/extensor E-C increased significantly with speed in both groups of subjects (P < 0.05) and tended to rise with muscle length as the knee was extended; peak values were generated at the most extended joint position (20 degrees-30 degrees). Although torque development patterns were symmetrical between the contralateral limbs in both groups, between-group comparisons revealed significantly higher flexor/extensor E-C ratios for the INJ group compared to the UNI group (P < 0.05), particularly at the fastest speed tested (60 degrees x s(-1)). The results indicate that joint position and movement speed influence the eccentric/concentric relationships of knee flexors and extensors. The INJ subjects appeared to accommodate to surgery by developing the eccentric function of their ACL and normal knee flexors, particularly at higher speeds and at more extended knee joint positions. This may assist in the dynamic stabilization of the knee at positions where ACL grafts have been reported to be most vulnerable to strain.     

Leg position learning by an insect: II. Motor strategies underlying learned leg extension

The patterns of myographic activity in the flexor and extensor tibiae muscles of the locust which accompany learned tibial extension were examined. Three distinct motor strategies were identified: (1) repeated flexion-extension movements, each of which resulted in a momentary excursion beyond the required, pre-set joint angle (demand angle) and in sum met the criterion for learning; (2) changes in basic muscle tonus, which resulted in maintained shifts in tibial position without discernible myographic activity; (3) tonic activity in the single slow excitatory motoneuron of the extensor tibiae ( SETi ) which produced maintained tibial extension. These strategies were selectively employed depending on the particular range of joint angle required. These strategies were compared and their effectiveness evaluated using a variety of behavioral criteria. Neuronal mechanisms which might underlie each of these strategies are discussed.     

Aquatic Coleoptera and Heteroptera inhabiting waterbodies from Berisso, Buenos Aires Province, Argentina

Coleoptera and Heteroptera associated with aquatic environments were studied at Berisso, near Rio de La Plata estuary (Buenos Aires Province, Argentina). Four waterbodies were characterized and compared: artificial pond, shallow pool, stream and artificial channel. Sampling was done twice a month, with a round sieve, for 12 months (April 1999 to April 2000). Sampling was quantified using a discrete unit of time (one hour/worker). Where floating vegetation was present, four 25 cm diameter samples were extracted and placed in a Berlese-Tullgren funnel for 48 hours. Temperature, pH and conductivity were measured. Specimens were preserved in 70 degrees ethanol. Similarities in taxonomic composition among sampling stations were quantified using Jaccard's index based on a presence/absence matrix for the insect fauna of each sampling station. A total of 68 species belonging to 8 families of Coleoptera and 11 families of Heteroptera were collected. The highest number of species (41) was recorded in the shallow pool (stream 34 species; artificial pond 29; artificial channel 25). The highest specific diversity values were observed during spring in all sampling stations. The highest frequency of Coleoptera was shown by Helochares talarum Fernández and Suphisellus nigrinus (Aubé) (?). In the Heteroptera it was shown by Lipostemmata humeralis Berg, Lipogomphus lacuniferus Berg and Rheumatobates bonariensis (Berg). The most abundant species were not necessarily the most frequent ones. Coleoptera is the most important group in species richness. Each environment had a taxocoenosis of Coleoptera and Heteroptera with inherent characteristics.     

Postnatal development of node-paranode regions in two hind limb nerves of the cat

Node-paranode regions of large myelinated axons from the nerves to the lateral gastrocnemius muscle (ankle extensor) and the anterior tibial muscle (ankle flexor) were studied in the cat during postnatal development and examined with regard to the occurrence of paranodal Schwann cell Marchi-positive bodies and mitochondria. It was found, in newborn kittens with respect to both parameters, that paranodes of flexor nerve fibers, being part of the functionally more developed ankle flexor reflex arc [cf. Mellström, A. (1971). Acta Physiol. Scand., 82, 477–489], appeared more mature than did those of extensor nerve fibers, which are part of the less developed ankle extensor reflex arc. It is concluded that the maturation of large feline hind limb muscle nerve fibers runs through a “nodalization” process similar to that described earlier for feline lumbar spinal root fibers [cf. Berthold, C.-H. (1973). Neurobiology, 3, 339–352] and that this normally occurring, rather striking remodeling of the node-paranode regions is likely to be functionally significant.     

Structure and physiology of the locust femoral chordotonal organ

The connective chordotonal organs (COs) in the femora of the prothoracic and mesothoracic legs of the locust Schistocerca gregaria are divided into two parts, the proximal and the distal scoloparia. The proximal scoloparium contains about 150 small neurons and is anchored to the femoral cuticle. The distal scoloparium contains about 50 larger neurons and is connected at its proximal end to both the cuticle and the flexor tibiae muscle.Records were made from the distal scoloparium, classifying units by spike size. The tibial position/total activity response curve is ∪-shaped but when a small number of units is selected the responses occur only when the tibia is on one side of its centre position. The tonic responses display considerable hysteresis and a degree of adaptation which varies with the tibial angle. Units with phasic and phasic-tonic responses are common and their responsiveness depends on the range of angles the tibia is moved through. The same units respond strongly to flexor tibiae contraction with the tibia either fixed or free, and so may serve as receptors for tension in that muscle.The CO mediates phasic resistance reflexes in all three extensor tibiae motoneurons and tonic reflexes in the extensor ‘slow’ neuron. It is suggested that the very detailed information furnished by the CO is used in a complex way in the control of the femoral muscles.     

Morphology of the elytral base sclerites

The elytral base sclerites (= sclerites located at the articular region between the forewing and thorax in Coleoptera) of selected taxa were examined and homologized. Although the elytral base sclerites are highly modified compared to the wing base sclerites of the other neopterans, they can be homologized by using the conservative wing flapping and folding lines as landmarks. A reduction of the first axillary sclerite was identified as a general trend of the elytral base sclerites, although the sclerite usually has a very important function to mediate flight power from the notum to the wing. This result indicates that the functional constraint against the basal sclerites is relaxed because of the lack of an ability to produce flight power by elytra. In contrast, the elytral folding system formed by the basal sclerites is well retained, which probably occurs because proper wing folding is a key for the shelter function of the elytra. The elytral base sclerites apparently contain more homoplasies than the serially homologous hindwing base sclerites of Coleoptera, which suggests that the structure is less useful for higher-level systematics. However, the faster evolutionary rate of the elytral base sclerites suggests there is potential for studying the lower-level phylogeny of Coleoptera.     

Glutamatergic transmission between antagonistic motor neurones in the locust

The pharmacology of the direct central connections between the fast extensor and flexor motor neurones of a locust (Schistocerca gregaria) hind leg was studied. A spike in the fast extensor produces an EPSP in the flexor motor neurones. Glutamate depolarized the flexor motor neurones when injected into the neuropil. Quisqualate, but not by kainate or NMDA, also depolarized the flexor motor neurones. The fast extensor was also depolarized by glutamate, and also by kainate, but not by quisqualate, AMPA or NMDA. The glutamate response in the flexor motor neurones and the EPSP evoked by a spike in FETi both had similar reversal potentials. The FETi-evoked EPSP was blocked by bath application of the glutamate antagonist glutamic acid diethyl ester. The responses of extrasynaptic somata receptors to glutamate were compared to the neuropil responses. Glutamate usually hyperpolarized the somata of FETi and the flexor motor neurones. The response of a flexor motor neurone to glutamate was abolished at potentials less negative than -90 mV. The results provide evidence for glutamate transmission at central synapses in the locust, and show that presumed synaptic receptors in the neuropil differ to the extrasynaptic soma response     

Tibial combs in the Cydnidae (Hemiptera: Heteroptera) and their functional, taxonomic and phylogenetic significance

Tibial combs in representatives of the family Cydnidae are described in detail for the first time. The structure was studied in 98 species of 58 genera representing all the subfamilies, among them 16 species were investigated using scanning electron microscopic (SEM) techniques. In addition, Parastrachia japonensis (Scott, 1880) of the family Parastrachiidae, and two species of Dismegistus Amyot and Serville, 1843 (a genus of uncertain systematic position within Pentatomoidea) have also been studied. Morphological terminology is proposed for all the structures connected with tibial combs and the term 'the tibial comb complex' is suggested; its functional, taxonomic and phylogenetic significance is also discussed. The genera of Cydnidae can be classified into two groups depending on differences in the tibial comb complex, when it is present; moreover, its absence in the tribe Scaptocorini (Cephalocteinae) is demonstrated for the first time and is regarded as an autapomorphy of this tribe. Data on the occurrence of tibial combs in other families of true bugs (Hemiptera: Heteroptera) are also briefly reviewed, and an anagenetic trend in their evolution in terrestrial Heteroptera is hypothesized. The presence of tibial combs on all legs is regarded as the most plesiomorphic state.     

Structure of aquatic assemblages of Coleoptera and Heteroptera in relation to habitat type and flood dynamic structure

The abundance and taxonomic composition of the aquatic insect fauna were investigated, with focus on adult water bugs, water beetles and water scavenger beetles (Heteroptera: Nepomorpha and Gerromorpha, and Coleoptera: Hydradephaga and Hydrophilidae) in two different freshwater habitats: (1) a periodically flooded area of the Special Zoological Reserve in Kopa?ki rit Nature Park, Croatia; and (2) melioration canals in the wider area of the Nature Park during 2005. Aquatic insects are generally abundant in various water systems, including floodplains that are exposed to water level fluctuations. Our aims were (1) to determine abundance and species richness in relation to habitat type; (2) to determine the influence of high flood peaks and oscillations during high water levels on the diversity of aquatic Coleoptera and Heteroptera in the flooded area; and (3) to identify characteristic species associated with each habitat type. We collected 71 species; 41 were captured at canals and 64 at the flooded area. Diversity of the two habitat types varied depending on the months but there were remarkable differences in species pool and their abundance. Both high and low water levels as well as oscillations during high water levels had major influence on species assemblages at the flooded area. Diversity of aquatic Coleoptera and Heteroptera was higher when the water level decreased after high water level peaks. A total of 11 species fulfilled the criteria for specificity and were sufficiently abundant to be suitable species characteristic for these two habitats. A higher proportion of significant characteristic species was present in the flooded area than in the canals. The presence of two Red List species of water beetles (Graphoderus bilineatus De Geer, 1774 and Berosus geminus Reiche et Saulcy, 1856) and nine significant characteristic species at the flooded area clearly indicates that the contribution of floodplains in maintaining freshwater biodiversity is not only important regionally but also at the international level. Also, our results suggest that the power of high water levels is an important factor that can be used in analyses on aquatic Coleoptera and Heteroptera assemblages, showing the uniqueness of large floodplain areas.     

Extensor motor neurons of the crayfish abdomen

Summary The somata of five deep extensor motoneurons of the third abdominal ganglion of the crayfish(Procambarus clarkii) were located and identified. The positions of these somata within the ganglion and their distal distribution to muscles have been mapped and were constant. The soma of the extensor inhibitor was noted to touch the soma of the flexor inhibitor. Three of the excitatory neurons were clustered near their exit route.Sensory and cord routes of activation of the extensor motoneurons were also found and were constant from preparation to preparation. Sub-threshold recording showed that these motoneurons exhibited radically different types of post-synaptic response to stimuli at different sites in the nervous system. No interaction between extensor motoneurons or between the extensor and flexor motoneurons was observed.     

Effects of Light on the Membrane Potential of Protoplasts from Samanea saman Pulvini : Involvement of K Channels and the H -ATPase

Rhythmic light-sensitive movements of the leaflets of Samanea saman depend upon ion fluxes across the plasma membrane of extensor and flexor cells in opposing regions of the leaf-movement organ (pulvinus). We have isolated protoplasts from the extensor and flexor regions of S. saman pulvini and have examined the effects of brief 30-second exposures to white, blue, or red light on the relative membrane potential using the fluorescent dye, 3,3′-dipropylthiadicarbocyanine iodide. White and blue light induced transient membrane hyperpolarization of both extensor and flexor protoplasts; red light had no effect. Following white or blue light-induced hyperpolarization, the addition of 200 millimolar K⁺ resulted in a rapid depolarization of extensor, but not of flexor protoplasts. In contrast, addition of K⁺ following red light or in darkness resulted in a rapid depolarization of flexor, but not of extensor protoplasts. In both flexor and extensor protoplasts, depolarization was completely inhibited by tetraethylammonium, implicating channel-mediated movement of K⁺ ions. These results suggest that K⁺ channels are closed in extensor plasma membranes and open in flexor plasma membranes in darkness and that white and blue light, but not red light, close the channels in flexor plasma membranes and open them in extensor plasma membranes. Vanadate treatment inhibited hyperpolarization in response to blue or white light, but did not affect K⁺ -induced depolarization. This suggests that white or blue light-induced hyperpolarization results from activation of the H⁺ -ATPase, but this hyperpolarization is not the sole factor controlling the opening of K⁺ channels.     

The extensor assembly in two species of opossum,Philander opossum and Didelphis marsupialis

In considering primate and hominoid phylogeny, the fundamental position assigned to opossums is explained partially by the characteristic morphology of their hands and feet. One of the main functional features of the human hand is the ability to make a stabilized arch of the finger. Because the extensor assembly plays a key role in establishing an arched finger, the extensor systems of the digits of both the hands and feet were studied in two species of opossum, Philander opossum and Didelphis marsupialis. In the foot, two extensor tendons join in each toe to form one tendinous plate, which inserts onto the base of the second phalanx. Lumbricals join this plate along the tibial side, and interosseus insertions are found, although a true interosseus wing is lacking. At the proximal interphalangeal level, a terminal tendon takes its origin from this tendinous plate. This terminal tendon is oval in cross-section and contains elastic structures. Oblique bands arise from this terminal tendon and run proximally along the proximal interphalangeal joint inserting onto the base of the first phalanx. There are elastic structures in the flexor tendon on the dorsal side near its site of insertion. In the hand, the main extensor tendons are arranged differently and the interossei contribute substantially to the extensor assembly. Otherwise, the extensor assembly of the hands and feet are quite similar. The function of the so-called paratendinous intravaginal flexors is discussed as are evolutionary aspects of the extensor assembly.