Knuckle-walking anteater: a convergence test of adaptation for purported knuckle-walking features of African Hominidae

Appeals to synapomorphic features of the wrist and hand in African apes, early hominins, and modern humans as evidence of knuckle-walking ancestry for the hominin lineage rely on accurate interpretations of those features as adaptations to knuckle-walking locomotion. Because Gorilla, Pan, and Homo share a relatively close common ancestor, the interpretation of such features is confounded somewhat by phylogeny. The study presented here examines the evolution of a similar locomotor regime in New World anteaters (order Xenarthra, family Myrmecophagidae) and uses the terrestrial giant anteater (Myrmecophaga tridactyla) as a convergence test of adaptation for purported knuckle-walking features of the Hominidae. During the stance phase of locomotion, Myrmecophaga transmits loads through flexed digits and a vertical manus, with hyperextension occurring at the metacarpophalangeal joints of the weight-bearing rays. This differs from the locomotion of smaller, arboreal anteaters of outgroup genera Tamandua and Cyclopes that employ extended wrist postures during above-branch quadrupedality. A number of features shared by Myrmecophaga and Pan and Gorilla facilitate load transmission or limit extension, thereby stabilizing the wrist and hand during knuckle-walking, and distinguish these taxa from their respective outgroups. These traits are a distally extended dorsal ridge of the distal radius, proximal expansion of the nonarticular surface of the dorsal capitate, a pronounced articular ridge on the dorsal aspects of the load-bearing metacarpal heads, and metacarpal heads that are wider dorsally than volarly. Only the proximal expansion of the nonarticular area of the dorsal capitate distinguishes knuckle-walkers from digitigrade cercopithecids, but features shared with digitigrade primates might be adaptive to the use of a vertical manus of some sort in the stance phase of terrestrial locomotion. The appearance of capitate nonarticular expansion and the dorsal ridge of the distal radius in the hominin lineage might be indicative of a knuckle-walking ancestry for bipedal hominins if interpreted within the biomechanical and phylogenetic context of hominid locomotor evolution.     

Electromyography of brachial muscles in Pan gorilla and hominoid evolution

Electromyographic studies on brachial muscles in a gorilla indicate that its elbow joint may be especially adapted for knuckle-walking and suspensory behavior. A close-packed positioning mechanism that minimizes muscular effort during full extension of the elbow joint is indicated by remarkably low levels of EMG in the brachial muscles, particularly during knuckle-walking and suspensory behavior on a trapeze. Extension of the elbow joint is facilitated by reduction of the olecranon process of the ulna, a feature that is attributable initially to aspects of an arboreal heritage in protogorilla and secondarily to selection for efficient knuckle-walking. Although notable differences exist between gorilla and man in known activity of the brachial muscles, the two species are strikingly similar in many basic features. Available evidence suggests that they share a common heritage of arboreal adaptation, including vertical climbing, hauling, hoisting, and suspensory behavior, perhaps more recently than some authors would care to admit. Knuckle-walking probably played an inconsequential role in the protohominid career. Selection for tool use, expecially involving powerful and rapid extension of the elbow joint, is the most reasonable explanation for the relatively more protuberant olecranon process in man by comparison with apes.     

EMG of chimpanzee shoulder muscles during knuckle-walking: problems of terrestrial locomotion in a suspensory adapted primate

By most accounts, the upper limb of the chimpanzee is primarily adapted to suspensory postures and locomotion. In order to determine how the derived morphology of the chimpanzee forelimb has affected the form of quadrupedal locomotion displayed by these animals, electromyographic activity patterns of 10 shoulder muscles during knuckle-walking in two chimpanzee subjects were analysed and compared to data on the opossum and cat taken from the literature. Telemetered electromyography coupled with simultaneous video recording was employed in order to study unfettered locomotion in the chimpanzee subjects.
Chimpanzees are characterized by a quadrupedal gait in which the hind limb overstrides the ipsilateral forelimb. Forelimb position in the plane of abduction/adduction is significantly affected by whether the hind limb passes inside or outside its ipsilateral forelimb. The degree of abduction adduction of the forelimb, in turn, influences many of the muscle activity patterns. That is, some muscles would be more frequently or less frequently active, depending on whether the arm was relatively abducted or adducted during a stride. Thus, there can be no single motor programme that generates the step cycle in chimpanzees.
While there are some parallels between muscle recruitment patterns for chimpanzee, opossum and cat quadrupedalism, the results of this study also indicate that many aspects of muscle use in chimpanzees have been significantly influenced by factors related to increased mobility of the upper limb. Finally, this study has revealed that moving the arm forward during swing phase of knuckle-walking is not a simple product of muscular elTort. and that other mechanisms must be involved. However, it is unclear at present exactly what these mechanisms may be.     

Posterior interosseous free flap with extended pedicle for hand reconstruction

The anatomy of the posterior interosseous vessels makes them suitable as a donor area of free flap. The skin island can be designed on the perforating vessels of the distal third of the forearm, up to the dorsal wrist crease, to increase the pedicle length (7 to 9 cm). A series of nine flaps transferred to reconstruct hand defects is presented. All flaps were designed over the dorsal distal forearm, and dimensions permitted direct closure of the donor site (up to 4 to 5 cm wide). Apart from a linear scar, donor morbidity was negligible. All transfers were successful. Although its dissection is somewhat tedious, the anatomy of the vascular pedicle is suitable for microanastomosis and the skin island is thin, although hairy. The posterior interosseous free flap with extended pedicle may be a good choice when limited amounts of thin skin and a long vascular pedicle are needed.     

Telemetered electromyography of flexor digitorum profundus and flexor digitorum superficialis in Pan troglodytes and implications for interpretation of the O. H. 7 hand.

The importance of knuckle-walking in the locomotor repertoire of African apes raises the possibility that the long digital flexors may be specially adapted more to meet the demands of ground quadrupedalism than those of suspension. To investigate this possibiltiy, the activities of the flexor digitorum superficialis and flexor digitorum profundus were studied by means of telemetered electromyography in three chimpanzees. Results clearly indicate that the fasciculi of the muscles to digits bearing weight in knuckle-walking are not called upon to contract in quadrupedal postures or in slow and moderately fast quadrupedal locomotion except to help clear the fingers from the ground as the forelimb begins its recovery stroke. At the most rapid speeds, a slight to moderate level of activity sometimes occurs in the latter half of stance phase. The long digital flexors display maximum and sustained activity during suspension. It is concluded that any role for these muscles in maintenance of stability at the metacarpophalangeal joints during knuckle-walking must be predominantly passive. Prominent markings for insertions of these muscles in a fossil hand (such as O.H. 7) suggest use of the forelimb in suspensory climbing behaviors.     

The functional anatomy of the hindlimb of some African Viverridae (Carnivora).

The functional anatomy of the hindlimb of 12 species of viverrids was studied with relation to locomotion. The animals were allocated to primary locomotor categories on the basis of their anatomy and locomotion. The climbing, arboreal walking category (Nandinia binotata) is characterized by a small sacroiliac articulation, the iliopsoas inserts onto a medially located lesser trochanter and the femoral condyles are not posteriorly placed. The hindfoot is plantigrade and its structure permits considerable movement. The pads are soft and the claws retractile. Representatives of the arboreal and terrestrial walking and jumping category (Genetta genetta, G. servalina, G. tigrina) have a plantigrade forefoot and digitigrade hindfoot. The lesser trochanter is more posteriorly placed than in the climbing category. A previously undescribed muscle, the caudofemoralis profundus extends from several anterior caudal vertebrae to the femur. The tibio-astragular joint restricts supination of the foot. There is little mediolateral movement in the digitidgrade foot. The claws are retractile. In the general terrestrial walking and scrambling group (Helogale parvula, Mungos mungo, Atilax paludinosus, Bdeogale crassicauda, Herpestes ichneumon, H. sanguineus) the animals have essentially similar hindlimbs except for size differences and modifications to the feet. Helogale and Mungos have large medial epicondyles on the humerus and large terminal phalanges. Bdeogale has a vestigial first metatarsal, while Atilax can splay its digits. In all species the distal phalanges are non-retractile. The trotting category (Civettictis civetta, Ichneumia albicauda) is characterized by longer epipodials and metapodials and a more proximal position of muscle bellies. Most of the adaptations minimize rotation, adduction and abduction of the leg and supination of the foot. The metatarsals are closely adjoined and the distal phalanx is stout and non-retractile. There appear to be two levels of locomotory adaptation. Major adaptations affect the whole appendicular skeleton and are used to assign animals to primary locomotor categories. Minor adaptations occur mainly in the foot and indicate the more specific habits of the animal.     

A rare insertion site for abductor pollicis longus and extensor pollicis brevis muscles

During an investigation performed on cadaver forearms in the anatomy department, an unusual insertion of the abductor pollicis longus (APL) muscle together with the extensor pollicis brevis (EPB) muscle was encountered unilaterally in a 40-year-old male cadaver forearm. APL originated from the posterior ulnar surface distal to the anconeus, the adjoining interosseous membrane and middle third of the posterior radial surface. It lay distal to the supinator muscle and close to the EPB, while the EPB arose from the posterior radial surface and from the adjacent interosseous membrane. These muscles were inserted to the palmar side of the base of the first metacarpal bone together. To our knowledge, this variation has not been cited in recent medical literature.     

Bone density spatial patterns in the distal radius reflect habitual hand postures adopted by quadrupedal primates

Primates adopt diverse hand postures during terrestrial and above-branch quadrupedal locomotion--knuckle-walking, digitigrady, and palmigrady--that incorporate varying degrees of wrist dorsiflexion (i.e., extension). Although relationships between hand postures, wrist joint range of motion, and the external properties of wrist bones (e.g., surface morphology) have been examined, the relationship between hand postures and the internal properties of wrist bones (e.g., bone density) remains largely unexplored. Because articular joint surfaces transmit mechanical loads between conjoining limb bones, measures of density (e.g., magnitudes and patterns) in the subchondral cortical plate of bone of the distal radius can be used to evaluate load regimes experienced by the wrist joint in different hand postures. We assessed apparent (i.e. optical) density patterns in several extant catarrhine primate taxa partitioned into different hand posture groups: knuckle-walking apes, digitigrade monkeys, and palmigrade monkeys. Computed tomography osteoabsorptiometry (CT-OAM) was used to construct maximum intensity projection (MIP) maps of apparent densities. High apparent density areas were characterized relative to a dorsal-volar reference plane and compared across hand posture groups. All groups had large percentage areas of high apparent density in the dorsal region of the distal radial articular surface. Only knuckle-walking apes, however, had a large percentage area of high apparent density in the volar region of the distal radial articular surface. These patterns are consistent with radiocarpal articulations in specific hand postures as evidenced by available radiographic data and suggest that the different habitual hand postures adopted by monkeys and African apes during quadrupedal locomotion have different stereotypic loading patterns. This has implications for understanding the functional morphology and evolution of knuckle-walking and digitigrade hand postures in primates.     

The innervation of the triangular fibrocartilage complex: nitric acid maceration rediscovered

Injury to the triangular fibrocartilage complex (TFCC) is frequently implicated in the etiology of ulnar-sided wrist pain. This study examines the nervous anatomy of the TFCC using a nitric acid maceration technique and attempts to correlate this information with known tear patterns. Ten fresh frozen cadaveric specimens were studied in detail. Gross dissection of each upper-extremity specimen included removal of all flexor and extensor tendons. After identification and labeling with permanent color of the ulnar nerve, dorsal sensory branch of the ulnar nerve, posterior interosseous nerve, anterior interosseous nerve, and median nerve, an en bloc excision of the distal radioulnar region was performed. Digestion of the soft tissue was performed with nitric acid at sequential concentrations of 50% and 33% for 9 of 10 specimens. The digestion was halted by immersing the specimen in a mixture of 10% formaldehyde and 1% glycerine. After removal of bone, the specimens were fixed in paraffin, sectioned, and stained with hematoxylin and eosin. Nine of the 10 specimens were studied microscopically to determine the contribution of the grossly identified nerves to each zone of the triangular fibrocartilage complex as defined by Palmer's classification of acute TFCC tears. The anterior interosseous, median, and superficial radial nerves did not contribute to the innervation of the TFCC. The intraarticular course of the peripheral nerves could not be defined in the one specimen that was not digested with nitric acid. Nitric acid maceration is a rediscovered technique for identifying the nervous anatomy of soft tissues. The study showed that the triangular fibrocartilage complex is innervated by branches of the posterior interosseous, ulnar, and dorsal sensory ulnar nerves in a fairly consistent manner. Improved treatment of TFCC tears may result from an enhanced understanding of the supporting structures' innervation and mechanical function.     

Ia presynaptic inhibition in human wrist extensor muscles: effects of motor task and cutaneous afferent activity.

The task-dependence of the presynaptic inhibition of the muscle spindle primary afferents in human forearm muscles was studied, focusing in particular on the modulation associated with the co-contraction of antagonist muscles and the activation of cutaneous afferents. The changes known to affect the motoneuron proprioceptive assistance during antagonist muscle co-activation in human leg and arm muscles were compared. The evidence available so far that these changes might reflect changes in the presynaptic inhibition of the muscle spindle afferent is briefly reviewed. The possible reasons for changes in presynaptic inhibition during the antagonist muscle co-contraction are discussed. Some new experiments on the wrist extensor muscles are briefly described. The results showed that the changes in the Ia presynaptic inhibition occurring during the co-contraction of the wrist flexor and extensor muscles while the hand cutaneous receptors were being activated (the subject's hand was clenched around a manipulandum) could be mimicked by contracting the wrist extensor muscles alone while applying extraneous stimulation to the hand cutaneous receptors. It is concluded that besides the possible contribution of inputs generated by the co-contraction of antagonist muscles and by supraspinal pathways, cutaneous inputs may play a major role in modulating the proprioceptive assistance during manipulatory movements.     

Inverse remodelling algorithm identifies habitual manual activities of primates based on metacarpal bone architecture

Previously, a micro-finite element (micro-FE)-based inverse remodelling method was presented in the literature that reconstructs the loading history of a bone based on its architecture alone. Despite promising preliminary results, it remains unclear whether this method is sensitive enough to detect differences of bone loading related to pathologies or habitual activities. The goal of this study was to test the sensitivity of the inverse remodelling method by predicting joint loading histories of metacarpal bones of species with similar anatomy but clearly distinct habitual hand use. Three groups of habitual hand use were defined using the most representative primate species: manipulation (human), suspensory locomotion (orangutan), and knuckle-walking locomotion (bonobo, chimpanzee, gorilla). Nine to ten micro-computed tomography scans of each species (\(n=48\) in total) were used to create micro-FE models of the metacarpal head region. The most probable joint loading history was predicted by optimally scaling six load cases representing joint postures ranging from \(-\,75^{\circ }\) (extension) to \(+\,75^{\circ }\) (flexion). Predicted mean joint load directions were significantly different between knuckle-walking and non-knuckle-walking groups (\(p<0.05\)) and in line with expected primary hand postures. Mean joint load magnitudes tended to be larger in species using their hands for locomotion compared to species using them for manipulation. In conclusion, this study shows that the micro-FE-based inverse remodelling method is sensitive enough to detect differences of joint loading related to habitual manual activities of primates and might, therefore, be useful for palaeoanthropologists to reconstruct the behaviour of extinct species and for biomedical applications such as detecting pathological joint loading.

     

Bone marrow aspiration the posterior iliac crest,an additional safe site

The posterior iliac crest is a readily accessible site for bone marrow aspiration which is safe, psychologically less traumatic, and affords representative samples of bone marrow similar to those obtained from the sternum, the vertebral spine and the anterior iliac crest.     

BONE MARROW ASPIRATION—The Posterior Iliac Crest,an Additional Safe Site

The posterior iliac crest is a readily accessible site for bone marrow aspiration which is safe, psychologically less traumatic, and affords representative samples of bone marrow similar to those obtained from the sternum, the vertebral spine and the anterior iliac crest.     

Knuckle-walking and the evolution of hominoid hands

Knuckle-walking is a pattern of digitigrade locomotion unique to African apes among Primates. Only chimpanzees and gorillas are specially adapted for supporting weight on the dorsal aspects of middle phalanges of flexed hand digits II–V. When forced to the ground, most orangutans assume one of a variety of flexed hand postures, but they cannot knuckle-walk. Some orangutans place their hands in palmigrade postures which are impossible to African apes. The knuckle-walking hands and plantigrade feet of African apes are both morphologically and adaptively distinct from those of Pongo, their nearest relative among extant apes. These features are associated with a common adaptive shift to terrestrial locomotion and support placing chimpanzees and gorillas in the same genus Pan. It is further suggested than Pan comprises the subgenera (a) Pan, including P. troglodytes and pygmy chimpanzees, and (b) Gorilla, including mountain and lowland populations of P. gorilla. African apes probably diverged from ancestral pongids that were specially adapted for distributing their weight in terminal branches of the forest canopy. Early adjustments to terrestrial locomotion may have involved fist-walking which later evolved into knuckle-walking. Orangutans continued to adapt to feeding and locomotion in the forest canopy and their hands and feet became highly specialized for four-digit prehension. Although chimpanzees retained arboreal feeding and nesting habits, they moved from tree to tree by terrestrial routes and became less restricted in habitat. While adapting to a diet of ground plants gorillas increased in size to the point that arboreal nesting is less frequent among them than among chimpanzees and orangutans. Early hominids probably diverged from pongids that had not developed prospective adaptations to knuckle-walking, and therefore did not evolve through a knuckle-walking stage. Initial adjustments to terrestrial quadrupedal locomotion and resting stance probably included palmigrade hand posturing. Their thumbs may have been already well developed as an adaptation for grasping during arboreal climbing. A combination of selection pressures for efficient terrestrial locomotor support and for object manipulation further advanced early hominid hands toward modern human configuration.     

EMG of scapulohumeral muscles in the chimpanzee during reaching and "arboreal" locomotion

Current views on the function of the deltoid and rotator cuff muscles emphasize their roles in arm-raising as participants in a scapulohumeral force "couple." The acceptance of such a mechanism is based primarily on a 1944 EMG study of human shoulder muscle action. More recently, it has been suggested that shoulder joint stabilization constitutes a second and equally important function of the cuff musculature, especially in nonhuman primates which habitually use their forelimbs in overhead postural and locomotor activities. Few comparative data exist, however, on the actual recruitment patterns of these muscles in different species. In order to assess the general applicability of a scapulohumeral force couple model, and the functional significance of the differential development of the scapulohumeral musculature among primate species, we have undertaken a detailed study of shoulder muscle activity patterns in nonhuman primates employing telemetered electromyography, which permits examination of unfettered natural behaviors and locomotion. The results of our research on the chimpanzee, Pan troglodytes, on voluntary reaching and two forms of "arboreal" locomotion reveal four ways in which previous perceptions of the function of the scapulohumeral muscles must be revised: 1) the posterior deltoid is completely different in function from the middle and anterior regions of this muscle; 2) the integrity of the glenohumeral joint during suspensory postures is not maintained solely by osseoligamentous structures; 3) the function of teres minor is entirely different from that of the other rotator cuff muscles and is more similar to the posterior deltoid and teres major; and 4) each remaining member of the rotator cuff plays a distinct, and often unique, role during natural behaviors. These results clearly refute the view that the muscles of the rotator cuff act as a single functional unit in any way, and an alternative to the force couple model is proposed.     

The antennal motor system of the stick insect Carausius morosus: anatomy and antennal movement pattern during walking

The stick insect Carausius morosus continuously moves its antennae during locomotion. Active antennal movements may reflect employment of antennae as tactile probes. Therefore, this study treats two basic aspects of the antennal motor system: First, the anatomy of antennal joints, muscles, nerves and motoneurons is described and discussed in comparison with other species. Second, the typical movement pattern of the antennae is analysed, and its spatio-temporal coordination with leg movements described. Each antenna is moved by two single-axis hinge joints. The proximal head-scape joint is controlled by two levator muscles and a three-partite depressor muscle. The distal scape-pedicel joint is controlled by an antagonistic abductor/ adductor pair. Three nerves innervate the antennal musculature, containing axons of 14-17 motoneurons, including one common inhibitor. During walking, the pattern of antennal movement is rhythmic and spatiotemporally coupled with leg movements. The antennal abduction/adduction cycle leads the protraction/retraction cycle of the ipsilateral front leg with a stable phase shift. During one abduction/adduction cycle there are typically two levation/depression cycles, however, with less strict temporal coupling than the horizontal component. Predictions of antennal contacts with square obstacles to occur before leg contacts match behavioural performance, indicating a potential role of active antennal movements in obstacle detection.     

Electromyography of knuckle-walking: results of four experiments on the forearm of Pan gorilla

Preliminary results of electromyographic (EMG) studies on the forearm of a gorilla provisionally support the hypothesis that special closepacked positioning mechanisms may characterize the wrist and metacarpophalangeal joints II–V in extant knuckle-walkers (chimpanzees and gorillas). We recommend that once the bony features, related to these close-packed positions are clearly identified, they may be employed strategically to discern evidence of a knuckle-walking heritage in the hands of extant hominoids, including man, and to trace the history of knuckle-walking in available fossils. This report contains results of the first successful employment of indwelling fine-wire electrode techniques to elucidate problems on the functional and evolutionary biology of great apes.     

人体测量指标与掌指纹特征之间的相关研究

本文对106名中国东北汉族女性进行了活体测量,并拓取了掌指纹。样本的年龄范围为18—34岁。所分析的人体测量指标共41项,掌指纹指标共59项。将人体测量指标与掌指纹指标同时输入电子计算机,进行了100项实验指标间的相关分析,并做了相关显著性检验。在41项人体测量指标中,有35项指标与掌指纹特征有相关关系。其中与掌指纹特征同时相关的人体测量特征有18项,与指纹特征相关的人体测量指标有2项,与掌纹相关的人体测量指标有15项。与掌指纹特征同时相关的人体测量特征,与遗传因素之间的相互关系大于与指纹相关的人体测量特征。与指纹相关的人体测量特征,与遗传因素的关系,要大于与掌纹相关的人体测量特征。     

Estimating the Functional Axis of the Primate Foot Using the Distribution of Plantar Muscles

Morton (American Journal of Physical Anthropology 5, 305–336, 1922) used the longest metatarsal, which he assumed functions as a lever during locomotion, to define the functional axis of the primate foot. In humans and apes, the functional foot axis lies on the second digit, whereas that of nonhominoid anthropoids is mostly on the third digit, suggesting that a medial shift of the functional axis occurred during primate foot evolution. Myological observations support this idea; the dorsal interossei of the human foot are arranged around the second digit, whereas those of nonhominoid anthropoids are around the third digit. However, it is still unclear when, why, and how such a change in foot musculature occurred. In addition, there is inconsistency among the limited number of studies that have examined foot musculature in apes. We examined modifications in the interosseous muscles of the chimpanzee, gibbon, spider monkey, and Japanese macaque in terms of the shift in the functional foot axis. We found that the dorsal interossei are arranged around the third digit; this is true even in the chimpanzee, whose functional axis based on metatarsal length lies on the second digit. This suggests that the change in the arrangement of the interosseous muscles phylogenetically lagged behind the shift of the osteological axis. Our results also indicate that the dorsal interossei are composite muscles consisting of the deep short flexors and the intermetatarsal abductors. We postulate that changes in the contributions of these 2 components to the formation of dorsal interossei likely occurred in the hominin lineage, resulting in the medial shift of the myological axis. The medial shift of the functional foot axis may have started with the elongation of the second metatarsal in the hominoid ancestors’ lineage, and was completed on the rearrangement of the interosseous muscles.