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Human evolution: taxonomy and paleobiology
- BERNARD WOOD, BRIAN G. RICHMOND
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- 01 July 2000, pp. 19-60
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This review begins by setting out the context and the scope of human evolution. Several classes of evidence, morphological, molecular, and genetic, support a particularly close relationship between modern humans and the species within the genus Pan, the chimpanzee. Thus human evolution is the study of the lineage, or clade, comprising species more closely related to modern humans than to chimpanzees. Its stem species is the so-called ‘common hominin ancestor’, and its only extant member is Homo sapiens. This clade contains all the species more closely-related to modern humans than to any other living primate. Until recently, these species were all subsumed into a family, Hominidae, but this group is now more usually recognised as a tribe, the Hominini. The rest of the review sets out the formal nomenclature, history of discovery, and information about the characteristic morphology, and its behavioural implications, of the species presently included in the human clade. The taxa are considered within their assigned genera, beginning with the most primitive and finishing with Homo. Within genera, species are presented in order of geological age. The entries conclude with a list of the more important items of fossil evidence, and a summary of relevant taxonomic issues.
Anatomy of the pig heart: comparisons with normal human cardiac structure
- SIMON J. CRICK, MARY N. SHEPPARD, SIEW YEN HO, LIOR GEBSTEIN, ROBERT H. ANDERSON
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- 01 July 1998, pp. 105-119
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Transgenic technology has potentially solved many of the immunological difficulties of using pig organs to support life in the human recipient. Nevertheless, other problems still remain. Knowledge of cardiac anatomy of the pig (Sus scrofa) is limited despite the general acceptance in the literature that it is similar to that of man. A qualitative analysis of porcine and human cardiac anatomy was achieved by gross examination and dissection of hearts with macrophotography. The porcine organ had a classic ‘Valentine heart’ shape, reflecting its location within the thorax and to the orientation of the pig's body (unguligrade stance). The human heart, in contrast, was trapezoidal in silhouette, reflecting man's orthograde posture. The morphologically right atrium of the pig was characterised by the tubular shape of its appendage (a feature observed on the left in the human heart). The porcine superior and inferior caval veins opened into the atrium at right angles to one another, whereas in man the orifices were directly in line. A prominent left azygous vein (comparable to the much reduced left superior caval or oblique vein in man) entered on the left side of the pig heart and drained via the coronary sinus. The porcine left atrium received only 2 pulmonary veins, whereas 4 orifices were generally observed in man. The sweep between the inlet and outlet components of the porcine right ventricle was less marked than in man, and a prominent muscular moderator band was situated in a much higher position within the porcine right ventricle compared with that of man. The apical components of both porcine ventricles possessed very coarse trabeculations, much broader than those observed in the human ventricles. In general, aortic-mitral fibrous continuity was reduced in the outlet component of the porcine left ventricle, with approximately two-thirds of the aortic valve being supported by left ventricular musculature. Several potentially significant differences exist between porcine and human hearts. It is important that these differences are considered as the arguments continue concerning the use of transgenic pig hearts for xenotransplantation.
The anatomy of language: contributions from functional neuroimaging
- CATHY J. PRICE
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- 23 November 2000, pp. 335-359
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This article illustrates how functional neuroimaging can be used to test the validity of neurological and cognitive models of language. Three models of language are described: the 19th Century neurological model which describes both the anatomy and cognitive components of auditory and visual word processing, and 2 20th Century cognitive models that are not constrained by anatomy but emphasise 2 different routes to reading that are not present in the neurological model. A series of functional imaging studies are then presented which show that, as predicted by the 19th Century neurologists, auditory and visual word repetition engage the left posterior superior temporal and posterior inferior frontal cortices. More specifically, the roles Wernicke and Broca assigned to these regions lie respectively in the posterior superior temporal sulcus and the anterior insula. In addition, a region in the left posterior inferior temporal cortex is activated for word retrieval, thereby providing a second route to reading, as predicted by the 20th Century cognitive models. This region and its function may have been missed by the 19th Century neurologists because selective damage is rare. The angular gyrus, previously linked to the visual word form system, is shown to be part of a distributed semantic system that can be accessed by objects and faces as well as speech. Other components of the semantic system include several regions in the inferior and middle temporal lobes. From these functional imaging results, a new anatomically constrained model of word processing is proposed which reconciles the anatomical ambitions of the 19th Century neurologists and the cognitive finesse of the 20th Century cognitive models. The review focuses on single word processing and does not attempt to discuss how words are combined to generate sentences or how several languages are learned and interchanged. Progress in unravelling these and other related issues will depend on the integration of behavioural, computational and neurophysiological approaches, including neuroimaging.
Obituary: PROFESSOR T. R. TREVOR-JONES, OBE
- BEVERLEY KRAMER
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- 01 June 1997, p. 629
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Professor T. R. Trevor-Jones, former Professor and Head of the Department of General Anatomy, Faculty of Dentistry, University of the Witwatersrand, died in Gauteng on 19th September 1996.
PROFESSOR ROBERT WALMSLEY (1906–1998)
- JOHN FRAME, DAVID SINCLAIR
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- 01 July 1999, p. 153
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Robert Walmsley, Emeritus Professor of Anatomy at the University of St Andrews, died on 24 August 1998 aged 92. He was appointed Bute Professor of Anatomy in St Andrews University in 1946, after a distinguished career in the University of Edinburgh, where he was appointed demonstrator in Anatomy with J. C. Brash as professor and E. B. Jamieson as senior lecturer. He carried out studies on the vertebral column and the knee joint with John Bruce (later Sir John Bruce), Professor of Surgery in Edinburgh, with whom he was associated in the production of 3 editions of a textbook of surgical anatomy. His work on the vascular system of the whale, conducted at the Carnegie Institute of Embryology in Baltimore, USA, was the subject of his thesis for the MD (Edinburgh University) which was awarded with honours and gold medal in 1937.
Synaptic organisation of the basal ganglia
- J. P. BOLAM, J. J. HANLEY, P. A. C. BOOTH, M. D. BEVAN
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- 01 May 2000, pp. 527-542
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The basal ganglia are a group of subcortical nuclei involved in a variety of processes including motor, cognitive and mnemonic functions. One of their major roles is to integrate sensorimotor, associative and limbic information in the production of context-dependent behaviours. These roles are exemplified by the clinical manifestations of neurological disorders of the basal ganglia. Recent advances in many fields, including pharmacology, anatomy, physiology and pathophysiology have provided converging data that have led to unifying hypotheses concerning the functional organisation of the basal ganglia in health and disease. The major input to the basal ganglia is derived from the cerebral cortex. Virtually the whole of the cortical mantle projects in a topographic manner onto the striatum, this cortical information is ‘processed’ within the striatum and passed via the so-called direct and indirect pathways to the output nuclei of the basal ganglia, the internal segment of the globus pallidus and the substantia nigra pars reticulata. The basal ganglia influence behaviour by the projections of these output nuclei to the thalamus and thence back to the cortex, or to subcortical ‘premotor’ regions. Recent studies have demonstrated that the organisation of these pathways is more complex than previously suggested. Thus the cortical input to the basal ganglia, in addition to innervating the spiny projection neurons, also innervates GABA interneurons, which in turn provide a feed-forward inhibition of the spiny output neurons. Individual neurons of the globus pallidus innervate basal ganglia output nuclei as well as the subthalamic nucleus and substantia nigra pars compacta. About one quarter of them also innervate the striatum and are in a position to control the output of the striatum powerfully as they preferentially contact GABA interneurons. Neurons of the pallidal complex also provide an anatomical substrate, within the basal ganglia, for the synaptic integration of functionally diverse information derived from the cortex. It is concluded that the essential concept of the direct and indirect pathways of information flow through the basal ganglia remains intact but that the role of the indirect pathway is more complex than previously suggested and that neurons of the globus pallidus are in a position to control the activity of virtually the whole of the basal ganglia.
Evolution of the human hand: approaches to acquiring, analysing and interpreting the anatomical evidence
- MARY W. MARZKE, R. F. MARZKE
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- 01 July 2000, pp. 121-140
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The discovery of fossil hand bones from an early human ancestor at Olduvai Gorge in 1960, at the same level as primitive stone tools, generated a debate about the role of tools in the evolution of the human hand that has raged to the present day. Could the Olduvai hand have made the tools? Did the human hand evolve as an adaptation to tool making and tool use? The debate has been fueled by anatomical studies comparing living and fossil human and nonhuman primate hands, and by experimental observations. These have assessed the relative abilities of apes and humans to manufacture the Oldowan tools, but consensus has been hampered by disagreements about how to translate experimental data from living species into quantitative models for predicting the performance of fossil hands. Such models are now beginning to take shape as new techniques are applied to the capture, management and analysis of data on kinetic and kinematic variables ranging from hand joint structure, muscle mechanics, and the distribution and density of bone to joint movements and muscle recruitment during manipulative behaviour. The systematic comparative studies are highlighting a functional complex of features in the human hand facilitating a distinctive repertoire of grips that are apparently more effective for stone tool making than grips characterising various nonhuman primate species. The new techniques are identifying skeletal variables whose form may provide clues to the potential of fossil hominid hands for one-handed firm precision grips and fine precision manoeuvering movements, both of which are essential for habitual and effective tool making and tool use.
Correspondence: Communication between the superior cervical sympathetic ganglion and the inferior laryngeal nerve
- IWAO SATO, TORU SATO, KAZUYUKI SHIMADA
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- 01 January 1997, pp. 147-148
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Complex arborisations occurs between the inferior ganglion of the vagus nerve and the superior cervical sympathetic ganglion (Braeucker, 1923; Fick, 1926; Siwe, 1931; Hoffman, 1957). The superior cervical sympathetic ganglion sends branches to the internal and the external carotid arteries, the inferior vagal ganglion, the superior laryngeal nerve and the cervical nerves, and provides superior cardiac and thyroid branches as well as the trunk that descends directly to the middle and inferior cervical sympathetic ganglia. There are communications between the vagus nerve (laryngeal branches) and the superior cervical sympathetic ganglion (SCSG). Cannizzaro et al. (1991) and Zerilli et al. (1994) reported abnormalities of sympathetic function among the effects of injury to the superior laryngeal nerve during thyroid surgery. The interconnections between these various nerves are therefore of clinical importance. We document here a rare example of complex communication between the vagus nerve and the SCSG in dissections of 113 adult (78 male, 35 female) Japanese cadavers. Both sides were examined in 88 cases, the right only in 18 and the left only in 7 (i.e. 201 sides in total).
The development and evolution of the pharyngeal arches
- ANTHONY GRAHAM
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- 23 August 2001, pp. 133-141
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A muscularised pharynx, with skeletal support, serving the dual functions of feeding and respiration, is a fundamental vertebrate characteristic. Embryologically, the pharyngeal apparatus has its origin in a series of bulges that form on the lateral surface of the embryonic head, the pharyngeal arches, whose development is complex. These structures are composed of a number of disparate embryonic cell types: ectoderm, endoderm, neural crest and mesoderm, whose development must be coordinated to generate the functional adult apparatus. In the past, most studies have emphasised the role played by the neural crest, which generates the skeletal elements of the arches, in directing pharyngeal arch development, but it has also become apparent that the endoderm plays a prominent role in directing arch development. Neural crest cells are not required for arch formation, their regionalisation nor to some extent their sense of identity. Furthermore, the endoderm is the major site of expression of a number of important signalling molecules, and this tissue has been shown to be responsible for promoting the formation of particular components of the arches. Thus vertebrate pharyngeal morphogenesis can now be seen to be a more complex process than was previously believed, and must result from an integration of both neural crest and endodermal patterning mechanisms. Interestingly, this also mirrors the fact that the evolutionary origin of pharyngeal segmentation predates that of the neural crest, which is an exclusively vertebrate characteristic. As such, the evolution of the vertebrate pharynx is also likely to have resulted from an integration between these 2 patterning systems. Alterations in the interplay between neural crest and endodermal patterning are also likely to be responsible for the evolutionary that occurred to the pharyngeal region during subsequent vertebrate evolution.
Progress in understanding hominoid dental development
- CHRISTOPHER DEAN
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- 01 July 2000, pp. 77-101
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Teeth preserve a record of the way they grow in the form of incremental markings in enamel, dentine and cementum. These make it possible to reconstruct cellular activity and the timing of dental development in living and fossil primates, including hominids. They also provide a way of exploring the mechanisms that underlie morphological change during evolution and the nature of the relationship between ontogeny and phylogeny. All living great apes are dentally mature by about 11 y, irrespective of their body mass. While the early period of root formation in living great apes is shorter than in modern humans, enamel takes approximately the same time to form, irrespective of how thick it is. In general, differences in the total time taken to form enamel seem not to be due to differences in the rate at which enamel and dentine are secreted, but rather to faster or slower rates of differentiation of ameloblasts and odontoblasts and therefore to the number of secretory cells active at any one time during tooth formation. Tooth size, especially height, may influence the sequence of appearance of tooth mineralisation stages. The space available in the jaws may also have an influence on both the timing of tooth bud/crypt appearance and the sequence of gingival emergence. When each of these potential influences on dental development are carefully considered, and incremental markings used to calibrate key events, the developing dentition can provide an estimate of the period of dental maturation in fossil hominoids. However, the influence of body mass on the period of dental development among primates remains unclear. The earliest hominoids, dated at around 18 Mya, may still have had modern monkey-like maturational profiles, and the earliest hominids, dated between 1.8 and 3.7 Mya, modern great ape-like maturational profiles. Exactly when the extended or prolonged modern human-like maturational profile first appeared remains debatable, but the most secure suggestion might be at the time of the appearance of the earliest archaic Homo sapiens, when brain size and body mass were finally both within the ranges known for modern humans. But at present we should not reject the hypothesis that an extended, modern human-like, maturational profile arose more than once during human evolution in parallel with an increase in brain size.