Estimación del sexo con metacarpos y metatarsos para población mexicana / Estimation of gender from metacarpals and metatarsals in a Mexican population

INTRODUCCIÓN: El objetivo de este estudio fue la obtención de funciones discriminantes para estimación del sexo a partir de mediciones directas en metacarpos y metatarsos para contribuir en la identificación de individuos desconocidos. MATERIAL Y MÉTODOS: Se analizaron métricamente los metacarpos y metatarsos de 112 esqueletos adultos contemporáneos (49 femeninos y 63 masculinos) de la Colección-UNAM del Laboratorio de Antropología Física, Facultad de Medicina, UNAM. Empleando un vernier digital se tomaron 5 medidas (longitud máxima y 4 anchuras) en cada uno de los huesos del metacarpo y del metatarso. RESULTADOS: Se desarrollaron 14 funciones discriminantes para los metacarpos, con porcentajes del 79,5% a 85,3% de asignación sexual correcta, siendo el segundo metacarpo el hueso más dimórfico de la muestra. Para el caso de los metatarsos se obtuvieron 5 funciones que van del 77,8% al 83,2% de certidumbre, siendo el primer metatarso el hueso más dimórfico. De manera general, las anchuras en ambas epífisis fueron las medidas más dimórficas. CONCLUSIONES: Las funciones discriminantes de metacarpos y metatarsos obtenidas presentan, de manera general, porcentajes por encima del 80%, lo cual concuerda con lo reportado para otras poblaciones; por lo tanto, pueden ser utilizadas en contextos forenses para la identificación humana, en restos completos o fragmentados, en el caso de no contar con otro elemento óseo, como la pelvis

INTRODUCTION: The aim of this study was to obtain discriminant functions for estimating gender from direct measurements of the metacarpal and metatarsal bones for identification of unknown individuals. MATERIAL AND METHODS: An analysis was performed on metacarpal and metatarsals bones of 112 adult contemporary skeletons (49 females and 63 males). The sample belongs to the Autonomous University of Mexico (UNAM) Collection from the Physical Anthropology Laboratory, UNAM Faculty of Medicine. Five measurements were taken (maximum length and four widths) of each metacarpal and metatarsal bones employing a digital calliper. RESULTS: Fourteen discriminant functions were developed for metacarpals with percentages from 79.5% to 85.3% of correct gender classification. The second metacarpal was the most dimorphic of the sample. For metatarsals, five discriminant functions were obtained, ranging from 77.8% to 83.2% of certainty. In this case the first metatarsal was the most dimorphic. In general terms, the widths of both epiphyses were the most dimorphic measurements. CONCLUSIONS: The discriminant functions of metacarpal and metatarsal bones obtained are generally above 80%, which is similar to reports from other populations. Therefore, it can be used in forensic contexts for human identification with complete or fragmented remains, in the cases where no other bone element is available, such as the pelvis

Morphology of the thoracic limb of goat as evidenced by gross osteology and radiology.

The objective of this study was to provide the detailed normal gross osteology and radiographic anatomy of the thoracic limb in goats as a reference for clinical use and in biomedical research. Radiography of the thoracic limb was performed in five small East African goats. Radiographic findings were correlated with bone specimens from four adult small East African goats. The scapula was narrow. The major tubercle was large and extended proximally above the head of the humerus. The lateral supracondylar crest was less prominent. The lateral and medial epicondyles of the humerus were almost of the same size. The lateral surface of the lateral condyle of the humerus presented a prominent depression for the origin of extensors of the carpus and digits. The cranially located radial notch was deep seated and the radial tuberosity was represented by a rough area located nearer to the head of the radius. The fifth metacarpal bone was seen in all animals. The morphology of the thoracic limb of small East African goats indicated the presence of powerful extensor muscles and is restricted to forward and backward movements as an adaptation to terrestrial lifestyle.

Human evolution. Comment on "Human-like hand use in Australopithecus africanus".

Skinner and colleagues (Research Article, 23 January 2015, p. 395), based on metacarpal trabecular bone structure, argue that Australopithecus africanus employed human-like dexterity for stone tool making and use 3 million years ago. However, their evolutionary and biological assumptions are misinformed, failing to refute the previously existing hypothesis that human-like manipulation preceded systematized stone tool manufacture, as indicated by the fossil record.

Human evolution. Response to Comment on "Human-like hand use in Australopithecus africanus".

Almécija and colleagues claim that we apply a simplified understanding of bone functional adaptation and that our results of human-like hand use in Australopithecus africanus are not novel. We argue that our results speak to actual behavior, rather than potential behaviors, and our functional interpretation is well supported by our methodological approach, comparative sample, and previous experimental data.

Comparación de dos métodos radiológicos para evaluación de densidad ósea en mujeres posmenopáusica / Comparison of two radiological methods for evaluation of bone density in postmenopausal women

Debido a la importancia del diagnóstico precoz de osteoporosis, fue objeto de este estudio realizar la comparación de dos métodos radiológicos convencionales para la evaluación de la densidad ósea en mujeres posmenopáusicas. Fueron seleccionadas imágenes de radiografía panorámica y de radiografía carpal, correspondiente a 68 pacientes de sexo femenino, con edades comprendidas entre los 49 y 80 años de edad, realizadas en la Clínica de Radiología Odontológica, para evaluación previa a la colocación de implantes. Para la interpretación de la densidad ósea en la mandíbula a través de las radiografías panorámicas fue utilizado el método del espesor cortical mandibular (PMI). Para la evaluación de las imágenes radiológicas obtenidas por la radiografía carpal, fue aplicado el método de la radiogrametría. Se concluye que existe correlación entre la presencia de una baja densidad ósea a nivel mandibular observada en la radiografía panorámica en las pacientes de la muestra, con la baja densidad ósea presentada en la radiografía carpal.

Due the importance of diagnosis precocious of osteoporosis, this study carried out the comparison of two conventional radiological methods for the evaluation of bone density in postmenopausal women. X-ray images of panoramic and carpal were selected, corresponding to 68 women between 49 and 80 years old, obtained at the Clinic of Dental Radiology, for holding dental implant. The interpretation of bone density in jaw on panoramic radiography was the method to determine mandibular cortical thickness. The carpal radiography was evaluated for the radiogrammetry method. It was concluded that there was a correlation between low bone density observed in the mandibular panoramic radiography with low bone density on carpal radiography.

Human evolution. Human-like hand use in Australopithecus africanus.

The distinctly human ability for forceful precision and power "squeeze" gripping is linked to two key evolutionary transitions in hand use: a reduction in arboreal climbing and the manufacture and use of tools. However, it is unclear when these locomotory and manipulative transitions occurred. Here we show that Australopithecus africanus (~3 to 2 million years ago) and several Pleistocene hominins, traditionally considered not to have engaged in habitual tool manufacture, have a human-like trabecular bone pattern in the metacarpals consistent with forceful opposition of the thumb and fingers typically adopted during tool use. These results support archaeological evidence for stone tool use in australopiths and provide morphological evidence that Pliocene hominins achieved human-like hand postures much earlier and more frequently than previously considered.

Proximo-distal gain of asymmetry in lamb metacarpals.

The ability of an organism to produce an ideal phenotype, despite the disturbances encountered during its development, is the causal mechanism of developmental stability. This ability is used to evaluate a variety of stress types and the genotypic ability to correct them. Geometric morphometric techniques were used to study the matched symmetry in form (size and shape) of right and left metacarpal bones in a sample of 48 lambs collected from abattoir facilities, on which 10 landmarks were located. Left and right metacarpal form showed statistically significant directional asymmetry, i.e. left and right body sides differed consistently from each other. The main shape differences were on the condylar reliefs of the distal part of the bone. These findings provide a reliable reference data set for future investigation on whether the morphology of the metacarpals is influenced by age and other factors such as the productive use of the animal (e.g. for meat, milk or wool).

Comparison of the anatomical dimensions and mechanical properties of the dorsoradial and anterior oblique ligaments of the trapeziometacarpal joint.

PURPOSE: The respective roles of the dorsoradial (DRL) and anterior oblique (AOL) ligaments in stability of the highly mobile trapeziometacarpal (TMC) joint remain disputed. Earlier publications have pointed to the AOL as the key stabilizing structure; yet, more recent publications have challenged the stabilizing role of the AOL, favoring the DRL as the main TMC joint stabilizer. We executed an anatomical study of the ligaments, including detailed dissection to quantify the length, width, and thickness of the AOL and DRL and tested the material properties of these ligaments. METHODS: Thirteen fresh frozen cadaveric thumbs from 9 specimens were used. Length, width, and thickness of the AOL and DRL were measured on magnetic resonance imaging and/or after dissection. Next, the first metacarpal and trapezium were isolated together with both ligaments, and both bones were cut sagittally to isolate a first metacarpal-AOL-trapezium and first metacarpal-DRL-trapezium complex from each thumb. These samples were subjected to cyclic loading in displacement-controlled tests. The obtained force-displacement curves were used to calculate stiffness and hysteresis of each sample. RESULTS: Our results showed that the DRL is significantly shorter and thicker than the AOL, which is thin and ill-defined. Our results also indicate that the DRL has a higher stiffness than the AOL, making it a more likely candidate to provide joint stability. CONCLUSIONS: Although the AOL has been asserted to be the primary restraint to dorsoradial subluxation, this view has been challenged over the past 10 years by several studies. These studies have shown the AOL to be relatively weak and compliant compared with the intermetacarpal and dorsoradial ligaments and have demonstrated that the DRL is the strongest and stiffest ligament of the TMC joint. Our studies confirm these findings. CLINICAL RELEVANCE: This study indicates that the DRL is relatively stiff and thick, suggesting it should be repaired or reconstructed when disrupted to restore stability of the TMC joint.

No sexual dimorphism in human prenatal metacarpal ratios.

BACKGROUND: Ratios of digit lengths are studied intensively as markers of prenatal sex hormone levels. AIM: Study sexual dimorphism in ratios of metacarpals, which received less attention. METHODS: We studied six metacarpal ratios in deceased human fetuses of ages 10 to 42weeks. RESULTS AND CONCLUSION: We found no indication of a sexual dimorphism at this early stage of development.

[The anatomical basis of the formation of the pedicled bone grafts on the upper extremity].

The study of the vascular bed of the upper extremities was performed by the method of anatomical preparation of 24 formalin-fixed cadaver specimens from 5 men and 7 women and by the injection of black latex into the arterial bed of 4 male and 4 female cadavers (16 specimens). The arteries, directly feeding the bones, and the arteries that provide blood supply to the muscles, attached to the bones, were studied. M. pectoralis major, m. pronator teres, m. pronator quadratus, mm. lumbricalis and interosseus were examined. These studies were followed by the experimental surgeries during which bone grafts on vascular pedicle were formed and moved. It was found that the feeding arteries of the bone grafts on musculo-vascular pedicle were: on the clavicula--the branches of a. thoracoacromialis, on the brachium--muscular branches of a. brachialis, on the proximal parts of forearm bones--muscular branches of a. radialis and ulnaris, on the distal parts of forearm bones--the branches of a. interosseous anterior, on the metacarpal bones--the branches of aa. metacarpalis palmaris and dorsalis. The size of the bone transplants is determined by the size of the defect of recipient field and varies from 3 to 8 cm. The displacement of vascularised bone graft can be made over the distance from 4 to 8 cm.

Elastographic characteristics of the metacarpal tendons in horses without clinical evidence of tendon injury.

Tendon and ligament injuries are common causes of impaired performance in equine athletes. Gray-scale ultrasonography is the current standard method for diagnosing and monitoring these injuries, however this modality only provides morphologic information. Elastography is an ultrasound technique that allows detection and measurement of tissue strain, and may provide valuable mechanical information about equine tendon and ligament injuries. The purpose of this study was to determine the feasibility, reproducibility, and repeatability of elastography; and to describe elastographic characteristics of metacarpal tendons in sound horses. Nineteen legs for 17 clinically sound horses without evidence of musculoskeletal pathology were included. Elastographic images of the superficial and deep digital flexor tendons and the branches of the suspensory ligament (tendon of the interosseous muscle) were described quantitatively and qualitatively. There was no statistically significant difference between operators (P = 0.86) nor within operators (P = 0.93). For qualitative assessments, reproducibility (0.46) was moderate and repeatability (0.78) was good. Similar to human Achilles tendons, equine tendons were classified as predominantly hard using elastography. There was no statistically significant difference in stiffness of the flexor tendons (P = 0.96). No significant difference in stiffness was found with altered leg position during standing (P = 0.84) and while nonweight bearing (P = 0.61). The flexor tendons were softer when imaged in longitudinal versus transverse planes (P < 0.01) however, the suspensory branches were not (P = 0.67). Findings supported future clinical application of elastography as a noninvasive "stall-side" imaging modality for evaluation of the tendons and ligaments of the distal forelimb in horses.

ADAM33 polymorphisms are associated with asthma and a distinctive palm dermatoglyphic pattern.

A close correlation between asthma and palm dermatoglyphic patterns has been observed in previous studies, but the underlying genetic mechanisms have not been investigated. A disintegrin and metalloprotein­33 (ADAM33) polymorphisms are important in the development of asthma and other atopic diseases. To investigate the underlying mechanisms of the association between asthma and distinctive palm dermatoglyphic patterns, thirteen ADAM33 single­nucleotide polymorphisms (SNPs) were analyzed for the association between asthma and palm dermatoglyphic patterns in a population of 400 asthmatic patients and 200 healthy controls. Based on the results, five SNPs, rs44707 (codominant model, P=0.031; log­additive model, P=0.0084), rs2787094 (overdominant model, P=0.049), rs678881 (codominant model, P=0.028; overdominant model, P=0.0083), rs677044 (codominant model, P=0.013; log­additive model, P=0.0033) and rs512625 (dominant model, P=0.033), were associated with asthma in this population. Two SNPs, rs44707 (dominant model, P=0.042) and rs2787094 (codominant model, P=0.014; recessive model, P=0.0038), were observed in the asthma patients with the distinctive palm pattern. As rs44707 and rs2787094 are associated with asthma and a distinctive palm pattern, the data suggest that ADAM33 polymorphisms are correlated with asthma and may be the underlying genetic basis of the association between asthma and palm dermatoglyphic patterns.

Design and validation of a simulator for equine joint injections.

Joint injections are commonly used in equine practice for diagnosis and treatment of joint disorders. Performing joint injections is hence an essential skill for equine practitioners. However, opportunities for veterinary students to practice this skill are often scarce in veterinary curricula. The aim of this study was to design and validate an equine joint injection simulator. We hypothesized that the simulator will enhance student ability and confidence in performing joint injections. The simulator was constructed around an equine forelimb skeleton with soft tissues rebuilt using building foam and rubber bands. An electrical circuit including a buzzer, a battery, wire wool in the joints, and a hypodermic needle at the end of the cable was incorporated. If the students placed the needle into the joint correctly, instant auditory feedback was provided by the buzzer. To validate the simulator, 45 veterinary students were allocated to three groups: cadaver limb, textbook, or simulator. Students' ability to perform joint injections was tested and students' opinions were evaluated with a questionnaire. The proportion of students performing a metacarpophalangeal (MCP) joint injection correctly was significantly higher in the cadaver (93%) and simulator (76%) groups compared to the textbook group (50%). There was no significant difference between groups for performing a distal interphalangeal (DIP) joint injection correctly. Students rated the learning experience with the cadaver and simulator group high and with the textbook group low. The joint injection simulator represents an affordable teaching aid that allows students to repeatedly practice this skill in their own time with immediate feedback.

Diffusion of contrast medium after four different techniques for analgesia of the proximal metacarpal region: an in vivo and in vitro study.

REASONS FOR PERFORMING STUDY: There is limited information on potential diffusion of local anaesthetic solution after various diagnostic analgesic techniques of the proximal metacarpal region. OBJECTIVE: To document potential distribution of local anaesthetic solution following 4 techniques used for diagnostic analgesia of the proximal metacarpal region. METHODS: Radiodense contrast medium was injected around the lateral palmar or medial and lateral palmar metacarpal nerves in 8 mature horses, using 4 different techniques. Radiographs were obtained 0, 10 and 20 min after injection and were analysed subjectively. A mixture of radiodense contrast medium and methylene blue was injected into 4 cadaver limbs; the location of the contrast medium and dye was determined by radiography and dissection. RESULTS: Following perineural injection of the palmar metacarpal nerves, most of the contrast medium was distributed in an elongated pattern axial to the second and fourth metacarpal bones. The carpometacarpal joint was inadvertently penetrated in 4/8 limbs after injections of the palmar metacarpal nerves from medial and lateral approaches, and in 1/8 limbs when both injections were performed from the lateral approach. Following perineural injection of the lateral palmar nerve using a lateral approach, the contrast medium was diffusely distributed in all but one limb, in which the carpal sheath was inadvertently penetrated. In 5/8 limbs, following perineural injection of the lateral palmar nerve using a medial approach, the contrast medium diffused proximally to the distal third of the antebrachium. CONCLUSIONS AND POTENTIAL RELEVANCE: Inadvertent penetration of the carpometacarpal joint is common after perineural injection of the palmar metacarpal nerves, but less so if both palmar metacarpal nerves are injected using a lateral approach. Following injection of the lateral palmar nerve using a medial approach, the entire palmar aspect of the carpus may be desensitised.

Avaliação da composição macroelementar do osso terceiro metacarpiano de equinos / Evaluation of the macro elemental composition of the equine third metacarpal bone

O terceiro osso metacarpiano equino é uma região de particular interesse devido ao grande número de lesões a que está sujeito. Assim, justifica-se o estudo detalhado da sua estrutura anatômica, dimensões e composição elementar para o aprimoramento de técnicas de diagnóstico, tratamento e prevenção de lesões. Neste trabalho,foi estudada a composição macroelementar óssea de 30 pares de osso terceiro metacarpiano equino e sua relação com a idade, sexo, peso, raça, alimentação e atividade dos animais. As concentrações médias de cálcio e fósforo das amostras foram 205 ± 62 mg/g e 97 ± 32 mg/g, respectivamente. A relação [Ca]/[P] encontrada foi de 2,12 ± 0,13, indicando que a proporção entre o cálcio e fósforo no tecido ósseo é constante e aproximadamente igual à razão 2:1. A análise estatística dos dados mostrou normalidade para todo o conjunto de medidas. A avaliação entre os animais com atividade física intensa e os animais com atividade física leve, em que a quantidade de material mineralizado para o primeiro e segundo conjuntos são, respectivamente, [Ca] = 222 ± 57 mg/g e [Ca] = 179 ± 47 mg/g, evidenciou a existência de correlação estatística entre o depósito de material mineral e a função exercida pelos animais. Para as demais características, não foram verificadas evidências estatísticas de inter-relações. Tais achados serão subsídios para estudos posteriores acerca de possíveis correlações com enfermidades de origem fisiológica ou nutricional frente à casuística de fraturas e outras afecções comuns ao aparelho locomotor equino.

The equine third metacarpal bone has been seen as a region of particular interest due to the large number of injuries to which it is subject. Thus, the detailed study of its anatomical structure, size and elemental composition is justified for the improvement of diagnostic techniques, treatment and prevention of injuries. In this work it has been studied the macro elemental composition of 30 pairs of equine third metacarpal bone and its relation with age, sex, weight, breed, nutrition and activity of animals. The average concentrations of calcium and phosphorus of the samples were 205 ± 62 mg/g and 97 ± 32 mg/g, respectively. The ratio [Ca] / [P] was found to be 2.12 ± 0.13, indicating that the ratio of calcium and phosphorus in bone tissue is constant and approximately equal to the ratio 2:1. The statistical analysis showed normal values for the entire set of measurements. In the evaluation of the animals with intense physical activity, and animals with light physical activity, it was found that the amount of mineralized material for the first and second sets respectively ([Ca] = 222 ± 57 mg/g [Ca] = 179 ± 47 mg/g), showing the existence of statistical correlation between the deposit of mineral material and the function performed by the animals. For the other characteristics were not found statistical evidence of correlations. These findings will be input for further studies of possible correlations with diseases of nutritional origin or physiological outside the series of fractures and other disease common to the equine locomotor system.

An anatomic study on the junctura tendinum in the 4th intermetacarpal space and its clinical implication.

We report results of anatomic study in the fourth intermetacarpal space, focusing on the pattern of junctura tendinum and variations of extensor tendons of the little finger with its clinical implication on snapping of the little finger. Fifty unpaired cadaveric hands were dissected from the wrist to the middle phalanx of the ring and little fingers. The type of junctura tendinum was judged based on Von Schroder's classification and the relationship with EDC were recorded. EDC to the little finger and EDM were dissected and the numbers were recorded. Forty six hands (92%) exhibited a junctura tendinum in the fourth intermetacarpal space and it was Type III in 42 hands (84%). The EDC-little finger was absent in 76% (38 of 50 hands). When present, EDC-little finger originated most commonly as single thin tendon. The absence of an EDC-little finger was associated with increased incidence of Type III junctura tendinum (37 of 38 hands). An EDM was present in all 50 hands running from the fifth dorsal compartment. Based on these clinical and anatomic studies, we considered that the snapping of the little finger is more likely subluxation of junctura tendinum rather than subluxation/dislocation of EDC of the little finger.

Changes in mineralised tissue at the site of origin of condylar fracture are present before athletic training in Thoroughbred horses.

AIM: To show that changes are present at the site of origin of metacarpal condylar fracture in young Thoroughbred horses before they enter race training. METHOD: Bone slices, 2 mm thick, in three mediolateral planes through the centre of rotation of the metacarpo-phalangeal joint (MCPJ) of both distal third metacarpal bones (Mc3) of 12 Thoroughbred horses aged 17 months, were imaged using point-projection digital X-ray imaging (muXR). RESULTS: In some horses, linear or ovoid radiolucency was found in articular calcified cartilage (ACC) and subchondral bone of the palmaro-distal aspect of the sagittal groove, exactly at the site of more advanced stages of condylar fatigue fracture. An incidental finding was ovoid radiolucency in the apex of the dorso-distal aspect of the sagittal ridge, with or without fragmentation or disturbance of the subchondral mineralised tissue line, resembling equine osteochondrosis. CONCLUSIONS AND CLINICAL RELEVANCE: The findings imply that the aetiology of condylar fatigue fracture in young Thoroughbred horses includes abnormality in development of the bone and joint that is present before athletic activity occurs.

[Does the thumb have two phalanges or three? Development of ideas since Aristotle]. / Le pouce a-t-il deux ou trois phalanges ? Evolution des idées depuis Aristote.

Many controversies mark the long road of the history of anatomy. The hand is not exempt of them. Even Galen's clear thinking, founded on the strict determinism between the structure of an organ and its function, and based on animal dissection, was criticized. In view of the structural complexity of the hand, we will limit our study to one of the most symptomatic conceptual disagreements: whether the human thumb has two or three phalanges, according to whether we include the first metacarpus, or if the thumb's first phalanx is considered as the initial element. According to the latter theory, there is a missing element in the first digital row, and this missing element is the metacarpus. This theory is ancient and its evolution throughout history is discussed in our study. Finally, we explain the origin and bases of the reasoning that led us to suggest the word 'metaphalanx' to designate the first metacarpus.

[Hands and feet of prosimians primates. Attempts of morphologic characterization]. / Mains et pieds des primates prosimiens. Essai de caractérisation morphologique.

The length of the carpus and tarsus, the metacarpus and metatarsus, the fingers and toes of 142 prosimian apes was measured. The relationship expressed as a percentage was drawn up for each individual between the length of each osseous part and that of its third metacarpal in order to eliminate the differences related to the size of the rest of the body. This ratio was compared with that of man. The characteristic variations appeared at the level of the subfamilies. CONCERNING THE HAND: The carpus presented the same values as that of man except for that of the indris, which was shorter. The thumb had proportionally the same length as that of man, sometimes longer and sometimes smaller as in the Eulemurs, Hapalidea, Megalapidea, Indrises, Daubentonia and Perodictus. The different metacarpals, including the fourth, were a little shorter than the third. In these subfamilies, the second ray was also often shorter and even much shorter in the Megalapidea and the Perodictus. The other rays were a little longer, in particular the fourth which could exceed the third in rather many subfamilies. CONCERNING THE FOOT: The length of the tarsus was extremely variable. It was twice larger in the Galagoidae, definitely larger in the tarsius and discreetly in the Hapalidae, a little smaller in the other Lemurs and much smaller in the other Prosimian apes, joining in that the near totality of the simians. The hallux was proportionally as long as that of man and sometimes even longer. The metatarsals were sometimes a little longer, sometimes less long, but always appreciably of the same length between them. The other toes were short at the aye aye (daubentonia), of which the foot appeared even smaller than that of man. The toes of the other prosimious resembled much to the fingers and in the propithecus and the perodictus, the fourth took gigantic proportions. There has been establishment of an anatomical relation and functional calculus between the length of the last three rays of the hands and the feet of prosimian apes and the biomechanics of their trapezometacarpal and their first cuneometacarpal joints.

Metacarpal proportions in Australopithecus africanus.

Recent work has shown that, despite being craniodentally more derived, Australopithecus africanus had more apelike limb-size proportions than A. afarensis. Here, we test whether the A. africanus hand, as judged by metacarpal shaft and articular proportions, was similarly apelike. More specifically, did A. africanus have a short and narrow first metacarpal (MC1) relative to the other metacarpals? Proportions of both MC breadth and length were considered: the geometric mean (GM) of articular and midshaft measurements of MC1 breadth was compared to those of MC2-4, and MC1 length was compared to MC3 length individually and also to the GM of MC2 and 3 lengths. To compare the extant hominoid sample with an incomplete A. africanus fossil record (11 attributed metacarpals), a resampling procedure imposed sampling constraints on the comparative groups that produced composite intrahand ratios. Resampled ratios in the extant sample are not significantly different from actual ratios based on associated elements, demonstrating the methodological appropriateness of this technique. Australopithecus africanus metacarpals do not differ significantly from the great apes in the comparison of breadth ratios but are significantly greater than chimpanzees and orangutans in both measures of relative length. Conversely, A. africanus has a significantly smaller breadth ratio than modern humans, but does not significantly differ from this group in either measure of relative length. We conclude that the first metacarpals of A. africanus are more apelike in relative breadth while also being more humanlike in relative length, a finding consistent with previous work on A. afarensis hand proportions. This configuration would have likely promoted a high degree of manipulative dexterity, but the relatively slender, apelike first metacarpal suggests that A. africanus did not place the same mechanical demands on the thumb as more recent, stone-tool-producing hominins.