Anatomical comparison across heads, fore- and hindlimbs in mammals using network models.

Animal body parts evolve with variable degrees of integration that nonetheless yield functional adult phenotypes: but, how? The analysis of modularity with Anatomical Network Analysis (AnNA) is used to quantitatively determine phenotypic modules based on the physical connection among anatomical elements, an approach that is valuable to understand developmental and evolutionary constraints. We created anatomical network models of the head, forelimb, and hindlimb of two taxa considered to represent a 'generalized' eutherian (placental: mouse) and metatherian (marsupial: opossum) anatomical configuration and compared them with our species, which has a derived eutherian configuration. In these models, nodes represent anatomical units and links represent their physical connection. Here, we aimed to identify: (1) the commonalities and differences in modularity between species, (2) whether modules present a potential phylogenetic character, and (3) whether modules preferentially reflect either developmental or functional aspects of anatomy, or a mix of both. We predicted differences between networks of metatherian and eutherian mammals that would best be explained by functional constraints, versus by constraints of development and/or phylogeny. The topology of contacts between bones, muscles, and bones + muscles showed that, among all three species, skeletal networks were more similar than musculoskeletal networks. There was no clear indication that humans and mice are more alike when compared to the opossum overall, even though their musculoskeletal and skeletal networks of fore- and hindlimbs are slightly more similar. Differences were greatest among musculoskeletal networks of heads and next of forelimbs, which showed more variation than hindlimbs, supporting previous anatomical studies indicating that in general the configuration of the hindlimbs changes less across evolutionary history. Most observations regarding the anatomical networks seem to be best explained by function, but an exception is the adult opossum ear ossicles. These ear bones might form an independent module because the incus and malleus are involved in forming a functional primary jaw that enables the neonate to attach to the teat, where this newborn will complete its development. Additionally, the human data show a specialized digit 1 module (thumb/big toe) in both limb types, likely the result of functional and evolutionary pressures, as our ape ancestors had highly movable big toes and thumbs.

Integration of the mammalian shoulder girdle within populations and over evolutionary time.

Morphological integration has the potential to link morphological variation within populations with morphological evolution among species. This study begins to investigate this link by comparing integration among shoulder girdle elements (e.g. scapular blade, glenoid, coracoid, etc.) during the origin and evolution of therian mammals, and within modern bat, opossum and mouse populations. In this study, correlations among skeletal elements and patterns of allometry are used as proxies for integration. Results suggest that shoulder girdle elements tended to vary and evolve independently during the origin of mammals and subsequent radiation of placentals, consistent with the elements' distinct developmental and evolutionary origins. This finding suggests that skeletal element correlations, and therefore integration, can be conserved over large taxonomic and temporal scales. However, marsupials display a different pattern in which shoulder girdle elements tend to be more integrated, with the exception of the coracoid. This finding is consistent with a shift in the pattern of skeletal element integration coincident with the appearance of the marsupial mode of reproduction. This finding provides further evidence that development can play a significant role in the establishment of patterns of skeletal element correlation and that patterns of skeletal element correlation can themselves evolve when faced with sufficient selective pressures.

Morphological and morphometric study of the opossum's dorsal root ganglia neurons.

The ultrastructural characteristics and the morphometric evaluation of the different types of neurons present in the dorsal root ganglia (DRG) of the South American opossum (Didelphis albiventris) were studied. Four adult male animals were used and the neurons from cervical and lumbar DRG were removed and processed for histological and transmission electron microscopy observations. The morphometric data were obtained from serial sections stained by H/E and Masson's trichrome. The number of neurons in cervical and lumbar DRG was 22 300 and 31 000, respectively. About 68% of the cervical neurons and 62.5% of the lumbar neurons presented areas up to 1300 µm(2) and were considered as the small neurons of the DRG. The ultrastructural observations revealed two morphological types of neurons: clear large neurons and dark small neurons. The nuclei of both cell types are spherical and the chromatin is disperse and rarefected. The cytoplasm of the dark small neuron is more electron dense and shows a regular distribution of small mitochondria and many rough reticulum cisterns in the periphery. A small Golgi apparatus was close to the nucleus and many disperse neurofilaments occupy most parts of the cytoplasm. Smooth reticulum cisterns are rare and lipofucsin-like inclusions are present at some points. In the clear large neurons, the organelles are homogenously scattered through the cytoplasm. The neurofilaments are close packed forming bundles and small mitochondria and rough reticulum cisterns are disperse. Lipofucsin-like inclusions are more frequent in these cells.

Skull modularity in neotropical marsupials and monkeys: size variation and evolutionary constraint and flexibility.

An organism is built through a series of contingent factors, yet it is determined by historical, physical, and developmental constraints. A constraint should not be understood as an absolute obstacle to evolution, as it may also generate new possibilities for evolutionary change. Modularity is, in this context, an important way of organizing biological information and has been recognized as a central concept in evolutionary biology bridging on developmental, genetics, morphological, biochemical, and physiological studies. In this article, we explore how modularity affects the evolution of a complex system in two mammalian lineages by analyzing correlation, variance/covariance, and residual matrices (without size variation). We use the multivariate response to selection equation to simulate the behavior of Eutheria and Metharia skulls in terms of their evolutionary flexibility and constraints. We relate these results to classical approaches based on morphological integration tests based on functional/developmental hypotheses. Eutherians (Neotropical primates) showed smaller magnitudes of integration compared with Metatheria (didelphids) and also skull modules more clearly delimited. Didelphids showed higher magnitudes of integration and their modularity is strongly influenced by within-groups size variation to a degree that evolutionary responses are basically aligned with size variation. Primates still have a good portion of the total variation based on size; however, their enhanced modularization allows a broader spectrum of responses, more similar to the selection gradients applied (enhanced flexibility). Without size variation, both groups become much more similar in terms of modularity patterns and magnitudes and, consequently, in their evolutionary flexibility.

Brief communication: Forelimb compliance in arboreal and terrestrial opossums.

Primates display high forelimb compliance (increased elbow joint yield) compared to most other mammals. Forelimb compliance, which is especially marked among arboreal primates, moderates vertical oscillations of the body and peak vertical forces and may represent a basal adaptation of primates for locomotion on thin, flexible branches. However, Larney and Larson (Am J Phys Anthropol 125 [2004] 42-50) reported that marsupials have forelimb compliance comparable to or greater than that of most primates, but did not distinguish between arboreal and terrestrial marsupials. If forelimb compliance is functionally linked to locomotion on thin branches, then elbow yield should be highest in marsupials relying on arboreal substrates more often. To test this hypothesis, we compared forelimb compliance between two didelphid marsupials, Caluromys philander (an arboreal opossum relying heavily on thin branches) and Monodelphis domestica (an opossum that spends most of its time on the ground). Animals were videorecorded while walking on a runway or a horizontal 7-mm pole. Caluromys showed higher elbow yield (greater changes in degrees of elbow flexion) on both substrates, similar to that reported for arboreal primates. Monodelphis was characterized by lower elbow yield that was intermediate between the values reported by Larney and Larson (Am J Phys Anthropol 125 [2004] 42-50) for more terrestrial primates and rodents. This finding adds evidence to a model suggesting a functional link between arboreality--particularly locomotion on thin, flexible branches--and forelimb compliance. These data add another convergent trait between arboreal primates, Caluromys, and other arboreal marsupials and support the argument that all primates evolved from a common ancestor that was a fine-branch arborealist.

An endoderm-specific transcriptional enhancer from the mouse Gata4 gene requires GATA and homeodomain protein-binding sites for function in vivo.

Several transcription factors function in the specification and differentiation of the endoderm, including the zinc finger transcription factor GATA4. Despite its essential role in endoderm development, the transcriptional control of the Gata4 gene in the developing endoderm and its derivatives remains incompletely understood. Here, we identify a distal enhancer from the Gata4 gene, which directs expression exclusively to the visceral and definitive endoderm of transgenic mouse embryos. The activity of this enhancer is initially broad within the definitive endoderm but later restricts to developing endoderm-derived tissues, including pancreas, glandular stomach, and duodenum. The activity of this enhancer in vivo is dependent on evolutionarily-conserved HOX- and GATA-binding sites, which are bound by PDX-1 and GATA4, respectively. These studies establish Gata4 as a direct transcriptional target of homeodomain and GATA transcription factors in the endoderm and support a model in which GATA4 functions in the transcriptional network for pancreas formation.

Isolation and characterization of a proteinaceous subnuclear fraction composed of nuclear matrix, peripheral lamina, and nuclear pore complexes from embryos of Drosophila melanogaster.

Morphologically intact nuclei have been prepared from embryos of Drosophila melanogaster by a simple and rapid procedure. These nuclei have been further treated with high concentrations of DNase I and RNase A followed by sequential extraction with 2% Triton X-100 and 1 M NaCl to produce a structurally and biochemically distinct preparation designated Drosophila subnuclear fraction I (DSNF-I). As seen by phase-contrast microscopy, DSNF-I is composed of material which closely resembles unfractionated nuclei; residual internal nuclear structures including nucleolar remnants are clearly visible. By transmission electron microscopy, nuclear lamina, pore complexes, and a nuclear matrix are similarly identified. Biochemically, DSNF-I is composed almost entirely of protein (greater than 93%). SDS PAGE analysis reveals several major polypeptides; species at 174,000, 74,000, and 42,000 predominate. A polypeptide coincident with the Coomassie Blue-stainable 174-kdalton band has been shown by a novel technique of lectin affinity labeling to be a glycoprotein; a glycoprotein of similar or identical molecular weight has been found to be a component of nuclear envelope fractions isolated from the livers of rats, guinea pigs, opossums, and chickens. Antisera against several of the polypeptides in DSNF-I have been obtained from rabbits, and all of them show only little or no cross-reactivity with Drosophila cytoplasmic fractions. Initial results of immunocytochemical studies, while failing to positively localize either the 174- or 16-kdalton polypeptides, demonstrate a nuclear localization of the 74-kdalton antigen in all of several interphase cell types obtained from both Drosophila embryos and third-instar larvae.

Convergent projection of three separate thalamic nuclei on to a single cortical area.

Three distinct sensory-motor nuclei in the thalamus project to parietal cortex in the Virginia opossum; the ventral posterior nucleus receives inputs from somatic sensory structures and projects to layers IV and III, the ventral anterolateral nucleus receives inputs from motor structures and projects to layers IV and III and inner I, and the central intralaminar nucleus receives inputs from sensory, motor, and other structures and projects to layers VI through outer I. The physiologically defined amalgamation of somatic sensory and motor cortex is correlated, therefore, with the extent of cortex that receives convergent somatic sensory and motor input from the thalamus.

Unique skull network complexity of Tyrannosaurus rex among land vertebrates.

Like other diapsids, Tyrannosaurus rex has two openings in the temporal skull region. In addition, like in other dinosaurs, its snout and lower jaw show large cranial fenestrae. In T. rex, they are thought to decrease skull weight, because, unlike most other amniotes, the skull proportion is immense compared to the body. Understanding morphofunctional complexity of this impressive skull architecture requires a broad scale phylogenetic comparison with skull types different to that of dinosaurs with fundamentally diverging cranial regionalization. Extant fully terrestrial vertebrates (amniotes) provide the best opportunities in that regard, as their skull performance is known from life. We apply for the first time anatomical network analysis to study skull bone integration and modular constructions in tyrannosaur and compare it with five representatives of the major amniote groups in order to get an understanding of the general patterns of amniote skull modularity. Our results reveal that the tyrannosaur has the most modular skull organization among the amniotes included in our study, with an unexpected separation of the snout in upper and lower sub-modules and the presence of a lower adductor chamber module. Independent pathways of bone reduction in opossum and chicken resulted in different degrees of cranial complexity with chicken having a typical sauropsidian pattern. The akinetic skull of opossum, alligator, and leatherback turtle evolved in independent ways mirrored in different patterns of skull modularity. Kinetic forms also show great diversity in modularity. The complex tyrannosaur skull modularity likely represents a refined mosaic of phylogenetic and ecological factors with food processing being probably most important for shaping its skull architecture. Mode of food processing primarily shaped skull integration among amniotes, however, phylogenetic patterns of skull integration are low in our sampling. Our general conclusions on amniote skull integrity are obviously preliminary and should be tested in subsequent studies. As such, this study provides a framework for future research focusing on the evolution of modularity on lower taxonomic levels.

An inhibitory innervation at the gastroduodenal junction.

Transverse muscle strips, 2-mm wide, were cut serially from the gastroduodenal junction in opossums, cats, dogs, and man. Electrical field stimulation with trains of rectangular current pulses of 0.5 ms in all opossums, all cats, some dogs, and the one human specimen induced relaxation in strips from the thickened circular muscle proximal to the mucosal junction. In some opossums weak relaxations also occurred in the first few strips below the mucosal junction. All other strips contracted or showed no response. This relaxation in opossums was abolished by tetrodotoxin but was not affected by antagonists to adrenergic and cholinergic transmission, nor by tripelennamine, methysergide, pentagastrin, secretin, cerulein, or cholecystokinin. Optimal frequency for stimulus-relaxation was 12 Hz. Chronaxie was 0.85 ms. The junctional strips also showed greater resistances to stretch than those remote from the junction. With apparent species variations, the junctional muscle possesses a nonadrenergic inhibitory innervation which is either absent or unexpressed in adjacent muscle of stomach and duodenum. This suggests the existence of a distinctive inhibitory neural control mechanism for pyloric muscle.

Nature of the vagal inhibitory innervation to the lower esophageal sphincter.

The purpose of the present study was to investigate the nature of the vagal inhibitory innervation to the lower esophageal sphincter in the anesthetized opossum. Sphincter relaxation with electrical stimulation of the vagus was not antagonized by atropine, propranolol, phentolamine, or by catechloamine depletion with reserpine. A combination of atropine and propranolol was also ineffective, suggesting that the vagal inhibitory influences may be mediated by the noncholinergic, nonadrenergic neurons. To determine whether a synaptic link with nicotinic transmission was present, we investigated the effect of hexamethonium on vagal-stimulated lower esophageal sphincter relaxation. Hexamethonium in doses that completely antagonized the sphincter relaxation in response to a ganglionic stimulant, 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), did not block the sphincter relaxation in response to vagal stimulation at 10 pulses per second, and optimal frequency of stimulation. A combination of hexamethonium and catecholamine depletion was also ineffective, but hexamethonium plus atropine markedly antagonized sphincter relaxation (P less than 0.001). Moreover, 4-(m-chlorophenyl carbamoyloxy)-2-butyltrimethylammonium chloride (McN-A-343), a muscarinic ganglionic stimulant, also caused relaxation of the lower esophageal sphincter. We suggest from these results that: (a) pthe vagal inhibitory pathway to the sphincter consists of preganglionic fibers which synapse with postganglionic neurons: (b) the synaptic transmission is predominantly cholinergic and utilizes nicotinic as well as muscarinic receptors on the postganglionic neuron, and; (c) postganglionic neurons exert their influence on the sphincter by an unidentified inhibitory transmitter that is neither adrenergic nor cholinergic.

The unique paired retinal vascular pattern in marsupials: structural, functional and evolutionary perspectives based on observations in a range of species.

BACKGROUND: In the few marsupial species studied to date that possess a retinal vasculature, the arterial and venous segments, down to the smallest calibre capillaries, have been shown to occur in pairs. It is a pattern seen in the marsupial central nervous system (CNS) but not in other tissues in this group or in any tissues in eutherian mammals. The aim of the present study was to investigate the presence of retinal vessels in a range of non-eutherian mammalian species (marsupials and monotremes) and to determine if the pattern of paired vessels was a widespread phenomenon within this animal group. METHODS: Species studied included a monotreme, the short-billed echidna (Tachyglossus aculeatus) and a range of Australian marsupials, the honey possum (Tarispedidae rostratus), fat-tailed dunnart (Sminthopsis crassicaudata), grey-bellied dunnart (Sminthopsis griseoventer), numbat (Myrmecobius fasciatus), broad-footed marsupial mouse (Antechinus godmani) and the North American opossum (Didelphis virginiana). Eyes were fixed in glutaraldehyde or paraformaldehyde and retinas were embedded in resin for light and electron microscopic analysis. RESULTS: Examination revealed that in those species with retinal vessels (fat-tailed dunnart, grey-bellied dunnart, numbat, marsupial mouse, North American opossum) the pattern of vessels differs from the conventional plexus-like arrangement of mammalian retinal vasculature (that is, anastomotic networks of capillaries between arterioles and venules). In marsupials retinal vessels always occur in closely related pairs, with the arteriolar limb usually situated on the vitread aspect. Vessels penetrate the retina and branch to form layers of paired capillaries as far as the outer nuclear layer in some species. The capillaries form blind-ended hairpin loops and display classical morphological features of CNS capillaries CONCLUSION: The phylogenetic relations of this vascular pattern in the marsupial CNS and retina, and in the CNS of a few other classes of non-mammalian vertebrates, suggest that retinal vascularisation may have evolved independently in marsupial and eutherian mammals and that the former may have evolved from a common primitive mammal-like reptilian ancestor which possessed paired vasculature in the CNS. Eutherian mammals may have evolved from an ancestor with anastomotic networks in the CNS or this pattern may have evolved later in eutherian mammal evolutionary radiation. The possible functional and physiological significance of the paired vessels is discussed.

Cranial endocasts from a growth series of Monodelphis domestica (Didelphidae, Marsupialia): A study of individual and ontogenetic variation.

Intraspecific variation (e.g., ontogenetic, individual, sexual dimorphic) is rarely examined among cranial endocasts (infillings of the braincase cavity) because of the difficulty in obtaining multiple specimens of a species, particularly fossil taxa. We extracted digital cranial endocasts from CT scans of a growth series of skulls of Monodelphis domestica, the gray short-tailed opossum, as a preliminary assessment of the amount of intraspecific variation in mammalian endocranial morphology. The goals of this study were 1) to provide an anatomical description to document developmental changes in endocranial morphology of M. domestica and 2) to examine ontogenetic and individual variation with respect to phylogenetic characters of endocranial cavities that are known to be variable between different mammalian taxa. In this study, "ontogenetic variation" refers to variation between specimens of different ages whereas "individual variation" (i.e., polymorphism) is restricted to variation between specimens of comparable age. Aside from size, changes in shape account for the greatest amount of morphological variation between the endocasts of different ages. Endocast length, width, and volume increase with age for the growth series. Relative olfactory bulb cast size increases with age in the growth series, but the relative size of the parafloccular casts shows a slight negative allometric trend through ontogeny. More than one-third of the phylogenetic characters of the endocranial cavity we examined showed some sort of variation (ontogenetic, individual, or both). This suggests that although endocasts are potentially informative for systematics, both ontogenetic and individual variation affect how endocranial characters are scored for phylogenetic analysis. Further studies such as this are necessary to determine the taxonomic extent of significant intraspecific variation of these endocranial characters.

Organization of brain extracellular matrix in the Chilean fat-tailed mouse opossum Thylamys elegans (Waterhouse, 1839).

We investigated the structural and molecular organization of the extracellular matrix in Thylamys elegans, a marsupial representative of the mammalian order Didelphimorphia. Perineuronal nets (PNs) associated with distinct types of neurons were visualized by detection of chondroitin sulfate proteoglycans and hyaluronan, and by labeling with Wisteria floribunda agglutinin (WFA), a marker for PNs in the mammalian brain. In the neocortex of Thylamys, these methods revealed PNs on pyramidal cells. In contrast, parvalbumin-immunoreactive interneurons in the neocortex and hippocampal formation (displaying robust, WFA-labeled PNs in placental mammals) were ensheathed only with a delicate rim of hyaluronan and proteoglycans not detectable with WFA. The absence of WFA staining was characteristic also of some subcortical regions which contained PNs intensely labeled for chondroitin sulfate proteoglycan and hyaluronan. However, corresponding to placental mammals, numerous subcortical nuclei showed clearly WFA-stained PNs. Similar as in placental mammals, cholinergic basal forebrain neurons and tyrosine hydroxylase-immunoreactive neurons of the substantia nigra and locus coeruleus were devoid of PNs. Together with our earlier study on Monodelphis, the present results reveal that South American opossums show either a particular "marsupial" or "Didelphid" type of extracellular matrix chemoarchitecture, supporting the view that these components may vary phylogenetically as integral parts of neuronal physiology at the systems and single cell level.

Efferent connections of the main olfactory bulb in the opossum (Monodelphis domestica): a characterization of the olfactory entorhinal cortex in a marsupial.

Olfactory projections have been investigated for decades, but few reports using modern, sensitive neural tracers are available. In marsupials, only lesion-degeneration studies exist and they are restricted to the genera Didelphis and Trichosurus. Some of the territories described as olfactory-recipient such as the upper portion of the rhinal fissure and the vomeronasal amygdala are, however, controversial. Also, the characterization of the olfactory portion of the entorhinal cortex is far from clear in acallosal mammals. The present report investigates, using biotinylated dextran-amine, the olfactory connections in the short-tailed opossum (Monodelphis domestica) and characterizes the olfactory portion of the entorhinal cortex in non-placental mammals. The data indicate that olfactory projections do not reach the upper portion of the rhinal fissure, but partially end in the vomeronasal amygdala, i.e., the medial and posteromedial cortical amygdaloid nuclei; thus, although olfactory and vomeronasal system have largely segregated outputs, areas of overlap should be restudied. The olfactory portion of the entorhinal cortex is much larger than previously described, extending up to the occipital pole of the cerebral hemisphere. Collectively, these data contribute to our understanding of the organization of the hippocampal formation in marsupials.

Topografia dos órgãos abdominais em Didelphis albiventris / Topography of abdominal organs in Didelphis albiventris

O conhecimento da localização dos órgãos nas diferentes regiões do corpo do animal é essencial para a prática clínica, cirúrgica e para o diagnóstico por imagem. O objetivo do estudo foi descrever a anatomia topográfica abdominal do Didelphisalbiventris. Foram utilizados quatro cadáveres (animais jovens), dois destes destinados para o estudo macroscópico em peças a fresco e os outros fixados em solução aquosa de formaldeído a 10%. Os cadáveres foram dissecados e as estruturas anatômicas identificadas, analisadas e fotografadas. A maioria dos órgãos localizados na região abdominal dos cadáveres da espécie D. albiventris apresentou posição similar aos dos caninos, porém, alguns órgãos e a localização de determinadas estruturas apresentaram particularidades importantes, como a presença dos ossos epipúbicos, a ausência do lobo hepático quadrado, a presença de um ceco desenvolvido e o cólon dividido em três segmentos.

The knowledge about localization of organs in different regions of the animal's body is essential for clinical, surgical and diagnostic imaging practice. The purpose of this study was to describe the abdominal topographic anatomy of Didelphis albiventris. Was used four dead bodys (young animals), two of these was intended for the macroscopic study of fresh pieces and the others fixed in 10% aqueous formaldehyde solution. The corpses was dissected and the anatomic structures was identified, analyzed and photographed. Most of the organs located in the abdominal region of cadavers from species D. albiventris presented structure and position similar to canines, however some of these organs and localization of structures presented important particularities, like the presence of epipubic bones, absence of square hepatic lobe, presence of an developed cecum and colon divided into three segments.

Phylogenetic evaluation of taxonomic definition of didelphid mouse opossum of the genus Thylamys from valleys of Coquimbo region, Chile.

Only two species of Didelphidae are currently recognized in Chile, the sister species Thylamys elegans, endemic of Mediterranean ecorregion and Thylamys pallidior, the inhabitant of the Puna and desert canyons. Three subspecies have been described for T. elegans: T. e. elegans, T. e. coquimbensis and T. e. soricinus. However, a recent study based on morphological analyses, synonymized T. elegans coquimbensis from the Coquimbo valleys (30-31° S) with T. pallidior and proposed that T. elegans and T. pallidior could be in sympatry at Coquimbo valleys between Fray Jorge (30°40'S) and Paiguano (30°02' S). We assess the current definition of T. e. coquimbensis and T. e. elegans, as well as this taxonomical conflict among the mouse opossums from the Coquimbo valleys through phylogenetic analyses of cytochrome b mitochondrial gene sequences. In this study, for the first time, we used specimens from the type localities of T. e. coquimbensis and T. e. elegans. In addition, we analyzed diagnostic cranial structures for this taxonomic revision. The results supported two allopatric clades, allowing us to keep the taxonomic definition of T. e. elegans and T. e. coquimbensis as phylogenetic reciprocal monophyletic clades and polyphyletic with T. pallidior. This result corroborates previous morphological analyses, which support that mouse opossums from the Coquimbo valleys are T. e. coquimbensis, thus extending its geographic distribution to the coast of Coquimbo and Atacama regions. We don´t have evidence for sympatric distribution between T. elegans and T. pallidior in the Coquimbo region.

Topografia dos órgãos abdominais em Didelphis albiventris / Topography of abdominal organs in Didelphis albiventris

O conhecimento da localização dos órgãos nas diferentes regiões do corpo do animal é essencial para a prática clínica, cirúrgica e para o diagnóstico por imagem. O objetivo do estudo foi descrever a anatomia topográfica abdominal do Didelphisalbiventris. Foram utilizados quatro cadáveres (animais jovens), dois destes destinados para o estudo macroscópico em peças a fresco e os outros fixados em solução aquosa de formaldeído a 10%. Os cadáveres foram dissecados e as estruturas anatômicas identificadas, analisadas e fotografadas. A maioria dos órgãos localizados na região abdominal dos cadáveres da espécie D. albiventris apresentou posição similar aos dos caninos, porém, alguns órgãos e a localização de determinadas estruturas apresentaram particularidades importantes, como a presença dos ossos epipúbicos, a ausência do lobo hepático quadrado, a presença de um ceco desenvolvido e o cólon dividido em três segmentos.

The knowledge about localization of organs in different regions of the animal’s body is essential for clinical, surgical and diagnostic imaging practice. The purpose of this study was to describe the abdominal topographic anatomy of Didelphis albiventris. Was used four dead bodys (young animals), two of these was intended for the macroscopic study of fresh pieces and the others fixed in 10% aqueous formaldehyde solution. The corpses was dissected and the anatomic structures was identified, analyzed and photographed. Most of the organs located in the abdominal region of cadavers from species D. albiventris presented structure and position similar to canines, however some of these organs and localization of structures presented important particularities, like the presence of epipubic bones, absence of square hepatic lobe, presence of an developed cecum and colon divided into three segments.

Functional shape of the skull in vertebrates: which forces determine skull morphology in lower primates and ancestral synapsids?

In order to determine the extent to which the shape of the synapsid skull is adapted for resisting the mechanical loads to which it is subjected, block- or simple plate-shaped finite-element models were constructed and loaded with external muscle and bite forces in locations estimated to resemble points of application of these forces. These 2D or 3D finite-element models were iteratively loaded and modified by removing elements that experience only low stresses, and the resulting morphologies of the models were compared with fossil skulls of synapsids and the skulls of extant mammals. The results suggest that the stress flows in these unspecific models are very similar to the arrangement of bone material in real skulls. Morphological differences between taxa depend on a few a priori conditions: length and position of the tooth rows in relation to the braincase, arrangement of muscles, position of the orbits, and position of the nasal opening. Given these initial conditions, finite-element analysis consistently reveals the close similarity between stress flows and real skulls. The major difference between mammal-like reptiles and primates is the size of the braincase. This difference accounts for most of the morphological divergence. The postorbital bar seems to be a constructional element of the skull, rather than a means to protect the eyes. The skull shapes of higher primates are determined mainly by masticatory forces and less by external forces acting on the head. This study demonstrates the utility of finite-element modeling for testing hypotheses regarding relationships between form and function in vertebrate skulls.