Meningeal arterial patterns in great apes: implications for hominid vascular evolution

Vascular microforamina and endocranial surface: Normal variation and distribution in adult humans: Vascular biology

The term craniovascular traits refers to the imprints left by arteries and veins on the skull bones. These features can be used in biological anthropology and archaeology to investigate the morphology of the vascular network in extinct species and past populations. Generally, the term refers to macrovascular features of the endocranial cavity, like those associated with the middle meningeal artery, venous sinuses, emissary foramina, and diploic channels. However, small vascular passages (here called microforamina or microchannels) have been occasionally described on the endocranial surface. The larger ones (generally with a diameter between 0.5 and 2.0 mm) can be detected through medical scanners on osteological collections. In this study, we describe and quantify the number and distribution of these microforamina in adult humans (N = 45) and, preliminarily, in a small sample of children (N = 7). Adults display more microchannels than juvenile skulls. A higher frequency in females is also observed, although this result is not statistically significant and might be associated with allometric cranial variations. The distribution of the microforamina is particularly concentrated on the top of the vault, in particular along the sagittal, metopic, and coronal sutures, matching the course of major venous sinuses and parasagittal bridging veins. Nonetheless, the density is lower in the region posterior to bregma. Beyond oxygenation, these vessels are likely involved in endocranial thermal regulation, infection, inflammation, and immune responses, and their distribution and prevalence can hence be of interest in human biology, evolutionary anthropology, and medicine.

The brain of Homo habilis: Three decades of paleoneurology

In 1987, Phillip Tobias published a comprehensive anatomical analysis of the endocasts attributed to Homo habilis, discussing issues dealing with brain size, sulcal patterns, and vascular traces. He suggested that the neuroanatomy of this species evidenced a clear change toward many cerebral traits associated with our genus, mostly when concerning the morphology of the frontal and parietal cortex. After more than 30 years, the fossil record associated with this taxon has not grown that much, but we have much more information on cranial and brain biology, and we are using a larger array of digital methods to investigate the paleoneurological variation observed in the human genus. Brain volume, the size of the frontal lobe, or the gross hemispheric asymmetries are still relevant issues, but they are considered to be less central than before. More attention is instead being paid to the cortical organization, the relationships with the cranial architecture, and the influence of molecular or ecological factors. Although the field of paleoneurology can currently count on a larger range of tools and principles, there is still a general lack of anatomical information on many endocranial traits. This aspect is probably crucial for the agenda of paleoneurology. More importantly, the whole science is undergoing a delicate change, because of the growing influence of the social environment. In this sense, the disciplines working with fossils (and, in particular, with brain evolution) should take particular care to maintain a healthy professional situation, avoiding an excess of speculation and overstatement.

Asymmetries of Cerebellar Lobe in the Genus Homo

The endocast was paid great attention in the study of human brain evolution. However, compared to that of the cerebrum, the cerebellar lobe is poorly studied regarding its morphology, function, and evolutionary changes in the process of human evolution. In this study, we define the major axis and four measurements to inspect possible asymmetric patterns within the genus Homo. Results show that significant asymmetry is only observed for the cerebellar length in modern humans and is absent in Homo erectus and Neanderthals. The influence of occipital petalia is obscure due to the small sample size for H. erectus and Neanderthals, while it has a significant influence over the asymmetries of cerebellar height and horizontal orientation in modern humans. Although the length and height of the Neanderthal cerebellum are comparable to that of modern humans, its sagittal orientation is closer to that of H. erectus, which is wider than that of modern humans. The cerebellar morphological difference between Neanderthals and modern humans is suggested to be related to high cognitive activities, such as social factors and language ability.

Stapedial Artery: From Embryology to Different Possible Adult Configurations

The stapedial artery is an embryonic artery that represents the precursor of some orbital, dural, and maxillary branches. Although its embryologic development and transformations are very complex, it is mandatory to understand the numerous anatomic variations of the middle meningeal artery. Thus, in the first part of this review, we describe in detail the hyostapedial system development with its variants, referring also to some critical points of ICA, ophthalmic artery, trigeminal artery, and inferolateral trunk embryology. This basis will allow the understanding of the anatomic variants of the middle meningeal artery, which we address in the second part of the review.

Carotid foramen size in the human skull tracks developmental changes in cerebral blood flow and brain metabolism

OBJECTIVES

In humans, neuronal processes related to brain development elevate the metabolic rate of brain tissue relative to the body during early childhood. This phenomenon has been hypothesized to contribute to slow somatic growth in preadolescent Homo sapiens. The uncoupling of the brain's metabolic rate from brain size during development complicates the study of the evolutionary emergence of these traits in the fossil record. Here, we extend a method previously developed to predict interspecific differences in cerebral blood flow (a correlate of cerebral glucose use) to predict ontogenetic changes in human brain metabolism.

MATERIALS AND METHODS

Radii of the carotid foramen from an ontogenetic series of modern human crania were used to predict blood flow rates through the internal carotid arteries (ICA), which were compared to empirically measured ICA flow and brain metabolism values.

RESULTS

Predictions of both absolute ICA blood flow rates and perfusion (ICA blood flow rates relative to brain size) generally match measured values in infancy and childhood. Maximum predicted ICA blood flow rates and perfusion were found to occur between ages 5 and 8, which roughly correspond to the age of maximum measured ICA blood flow rate and absolute and brain mass-specific rate of whole brain glucose uptake.

DISCUSSION

These findings suggest that, during human growth and development, the size of the carotid foramen corresponds well to blood flow requirements through the ICA, and the method tested here may provide new opportunities for studying developmental changes in brain metabolism using osteological samples, including fossil hominins.

Functional craniology and brain evolution: from paleontology to biomedicine

Anatomical systems are organized through a network of structural and functional relationships among their elements. This network of relationships is the result of evolution, it represents the actual target of selection, and it generates the set of rules orienting and constraining the morphogenetic processes. Understanding the relationship among cranial and cerebral components is necessary to investigate the factors that have influenced and characterized our neuroanatomy, and possible drawbacks associated with the evolution of large brains. The study of the spatial relationships between skull and brain in the human genus has direct relevance in cranial surgery. Geometrical modeling can provide functional perspectives in evolution and brain physiology, like in simulations to investigate metabolic heat production and dissipation in the endocranial form. Analysis of the evolutionary constraints between facial and neural blocks can provide new information on visual impairment. The study of brain form variation in fossil humans can supply a different perspective for interpreting the processes behind neurodegeneration and Alzheimer’s disease. Following these examples, it is apparent that paleontology and biomedicine can exchange relevant information and contribute at the same time to the development of robust evolutionary hypotheses on brain evolution, while offering more comprehensive biological perspectives with regard to the interpretation of pathological processes.

Variations and asymmetries in regional brain surface in the genus Homo

Paleoneurology is an important field of research within human evolution studies. Variations in size and shape of an endocast help to differentiate among fossil hominin species whereas endocranial asymmetries are related to behavior and cognitive function. Here we analyse variations of the surface of the frontal, parieto-temporal and occipital lobes among different species of Homo, including 39 fossil hominins, ten fossil anatomically modern Homo sapiens and 100 endocasts of extant modern humans. We also test for the possible asymmetries of these features in a large sample of modern humans and observe individual particularities in the fossil specimens. This study contributes important new information about the brain evolution in the genus Homo. Our results show that the general pattern of surface asymmetry for the different regional brain surfaces in fossil species of Homo does not seem to be different from the pattern described in a large sample of anatomically modern H. sapiens, i.e., the right hemisphere has a larger surface than the left, as do the right frontal, the right parieto-temporal and the left occipital lobes compared with the contra-lateral side. It also appears that Asian Homo erectus specimens are discriminated from all other samples of Homo, including African and Georgian specimens that are also sometimes included in that taxon. The Asian fossils show a significantly smaller relative size of the parietal and temporal lobes. Neandertals and anatomically modern H. sapiens, who share the largest endocranial volume of all hominins, show differences when considering the relative contribution of the frontal, parieto-temporal and occipital lobes. These results illustrate an original variation in the pattern of brain organization in hominins independent of variations in total size. The globularization of the brain and the enlargement of the parietal lobes could be considered derived features observed uniquely in anatomically modern H. sapiens.

Soft-tissue anatomy of the primates: phylogenetic analyses based on the muscles of the head, neck, pectoral region and upper limb, with notes on the evolution of these muscles

Apart from molecular data, nearly all the evidence used to study primate relationships comes from hard tissues. Here, we provide details of the first parsimony and Bayesian cladistic analyses of the order Primates based exclusively on muscle data. The most parsimonious tree obtained from the cladistic analysis of 166 characters taken from the head, neck, pectoral and upper limb musculature is fully congruent with the most recent evolutionary molecular tree of Primates. That is, this tree recovers not only the relationships among the major groups of primates, i.e. Strepsirrhini {Tarsiiformes [Platyrrhini (Cercopithecidae, Hominoidea)]}, but it also recovers the relationships within each of these inclusive groups. Of the 301 character state changes occurring in this tree, ca. 30% are non-homoplasic evolutionary transitions; within the 220 changes that are unambiguously optimized in the tree, ca. 15% are reversions. The trees obtained by using characters derived from the muscles of the head and neck are more similar to the most recent evolutionary molecular tree than are the trees obtained by using characters derived from the pectoral and upper limb muscles. It was recently argued that since the Pan/Homo split, chimpanzees accumulated more phenotypic adaptations than humans, but our results indicate that modern humans accumulated more muscle character state changes than chimpanzees, and that both these taxa accumulated more changes than gorillas. This overview of the evolution of the primate head, neck, pectoral and upper limb musculature suggests that the only muscle groups for which modern humans have more muscles than most other extant primates are the muscles of the face, larynx and forearm.

A new Homo erectus (Zhoukoudian V) brain endocast from China

A new Homo erectus endocast, Zhoukoudian (ZKD) V, is assessed by comparing it with ZKD II, ZKD III, ZKD X, ZKD XI, ZKD XII, Hexian, Trinil II, Sambungmacan (Sm) 3, Sangiran 2, Sangiran 17, KNM-ER 3733, KNM-WT 15 000, Kabwe, Liujiang and 31 modern Chinese. The endocast of ZKD V has an estimated endocranial volume of 1140 ml. As the geological age of ZKD V is younger than the other ZKD H. erectus, evolutionary changes in brain morphology are evaluated. The brain size of the ZKD specimens increases slightly over time. Compared with the other ZKD endocasts, ZKD V shows important differences, including broader frontal and occipital lobes, some indication of fuller parietal lobes, and relatively large brain size that reflect significant trends documented in later hominin brain evolution. Bivariate and principal component analyses indicate that geographical variation does not characterize the ZKD, African and other Asian specimens. The ZKD endocasts share some common morphological and morphometric features with other H. erectus endocasts that distinguish them from Homo sapiens.

The middle meningeal artery: from clinics to fossils

INTRODUCTION

Although research today ranges from molecular to universe scale, many issues regarding gross anatomy remain totally neglected. Within the framework of the endocranial morphogenesis and evolution, understanding the role and variation of the middle meningeal artery relies upon the very limited, scattered, and descriptive information available. The meninges are supplied by branches originating from both the internal and external carotid arteries, often converging in the same networks and hence raising questions on the homology and embryogenesis of these vessels. The middle meningeal artery is often ligated during craniotomies, with no apparent impairment of the cerebral functional processes. The exact physiological role of this extended vascular system, together with the adaptations and selective pressure associated with its evolutionary characterization, have generally been ignored.

THE MIDDLE MENINGEAL VESSELS IN NONHUMAN PRIMATES

Anthropologists have made many attempts to quantify and qualify the differences and variation between and within human and nonhuman primates, with scarce results due to the blurry morphology of the vascular networks. Living apes and humans probably have meningeal vessels originating from different embryogenetic processes, further hampering easy phylogenetic comparisons. Generally, monkeys and apes display a larger component derived from the internal carotid artery and its ophthalmic branch.

EVOLUTION AND MORPHOLOGICAL VARIATION IN FOSSIL HOMINIDS

The fossil endocasts partially show the traces of the middle meningeal vessels, allowing some hypotheses on the evolution of these structures. In contrast with modern humans, some extinct groups show a dominance of the posterior branch over the anterior one. The most interesting features are associated with the variation of the middle branch, which supplies the parietal areas. In any case, the most striking difference between the modern and non-modern humans regard the definite increase in the number and complexity of the anastomoses and reticulation in the former. This may be either the simple result of a larger percentage of traces left by the soft tissue or be associated with a more developed vascular network.

PERSPECTIVES

Tools are needed to quantify and qualify the morphogenesis and variations of the middle meningeal artery. Supposing these vessels are not strictly necessary in the adult age, the evolutionary pressure shaping their structure may have been associated with early life stages. Apart from oxygenation, another function which deserves attention is thermoregulation, considering the metabolic loadings of the cerebral mass.

Hominid evolution of the arteriovenous system through the cranial base and its relevance for craniosynostosis

OBJECTIVE

This paper discusses how the evolving hominid architecture of the arteriovenous system through the cranial base diverted foreseeable pathology in the human brain.

MATERIALS AND METHODS

Bipedal upright posture was an early adaptation in mosaic morphological pattern changes in hominid evolution; a key feature, the ability of blood to flow either to vertebral or internal jugular venous systems. Encephalization punctuated hominid evolution, its vulnerable feature, a lower threshold for thermal damage. Comparative analysis of ape and human skulls show "fingerprint" structures, revealing big changes in pattern complexity of the cranial vascular tree. Clues to structural/functional changes span data for apes, humans, and hominid fossils. Here, the increasing vascular network, Australopithecus to Homo sapiens, necessitated changes in the blood flow patterns. The transverse-sigmoid (T/S) and occipital-marginal (O/M) venous networks accommodated hydrostatic changes of blood flow, regulating temperature uniquely: the O/M system enlarged, allowing blood to flow straight down into the vertebral plexus without cooling, and added a vast network of emissary/diploic veins, acting as a brain cooling "radiator." This O/M system was fixed in the Australopithecus robustus lineage, p = 0.000001; high frequencies of emissary foramen were selected for over time. Ontologically, the human neonatal O/M system is fully developed; emissary/diploic veins are established by age 5, setting conditions for selective brain cooling.

CONCLUSION

The Radiator Theory is the evolution of the functionally efficient brain cooling system, fixed in the A. robustus lineage, tying hydrostatic consequences of bipedalism with release of a "thermal constraint" on the encephalizing brain, and reflected in our own ontogeny.

Endocranial cast of HexianHomo erectus from South China

In this paper, we present data on the morphological features and linear measurements for the Hexian Homo erectus and other comparative endocasts, in order to highlight variation during human brain evolution. The endocast of Hexian was reconstructed in 1982, and an endocranial volume of 1,025 ml was estimated. The geological age is about 412 ka, or roughly contemporaneous with the Zhoukoudian (ZKD) specimens. There are some differences between Hexian and the modern Chinese male endocasts in our sample, including low position of the greatest breadth, low maximum height, a well-marked and prominent frontal keel, the flat surface of the frontal lobes, prominent sagittal keel along the center frontal and parietal lobes, depressed Sylvian areas and parietal lobes superiorly, strong posterior projection of the occipital lobes, anterior position of the cerebellar lobes relative to the occipital lobes, and the relative simplicity of the meningeal vessels. Compared with the ZKD, Indonesian, and African Homo erectus specimens, Hexian has more morphological features in common with ZKD. Principal component analyses indicate that Hexian is closest to the ZKD Homo erectus compared with the modern Chinese and other Homo erectus, but its great breadth distinguishes it. Metric analyses show that the brain height, frontal breadth, cerebral height, frontal height, and parietal chord from Homo erectus to modern humans increased, while the length, breadth, frontal chord, and occipital breadth did not change substantially.

CT-based description and phyletic evaluation of the archaic human calvarium from Ceprano, Italy

The discovery in 1994, of a fossilized human calvarium near Ceprano, Italy, dated about 800-900 thousand years before present, opened a new page for the study of human evolution in Europe. It extended the continental fossil record over the boundary between Early and Middle Pleistocene for the first time and revealed the cranial morphology of humans that where probably ancestral to both Neanderthals and modern Homo sapiens. A tomographic analysis of the Italian specimen is reported here in order to describe size and shape, vascular traces, and other features of the endocranium, as well as some relevant ectocranial traits (particularly of the frontal region). Our results show that the Ceprano calvarium displays plesiomorphies shared by early Homo taxa, involving a general archaic phenotype. At the same time, the presence of some derived features suggests a phylogenetic relationship with the populations referred to the subsequent polymorphic species H. heidelbergensis. The morphology of the supraorbital structures is different from the double-arched browridge of the African H. ergaster, while its superior shape shows similarities with African Middle Pleistocene specimens (Bodo, Kabwe). In contrast, the relationship between supraorbital torus and frontal squama points to an archaic pattern of the relationship between face and vault, associated to moderately narrow frontal lobes and limited development of the upper parietal areas. Despite a nonderived endocranial shape, the increase of cranial capacity (related to a general endocranial widening) and the probable absence of a clear occipital projection also suggest an evolutionary independence from the Asian H. erectus lineage. This analysis therefore supports the conclusion that the Ceprano calvarium represents the best available candidate for the ancestral phenotype of the cranial variation observed among Middle Pleistocene fossil samples in Africa and Europe. Nevertheless, a proper taxonomic interpretation of this crucial specimen remains puzzling.

The Brain of LB1, Homo floresiensis

The brain of Homo floresiensis was assessed by comparing a virtual endocast from the type specimen (LB1) with endocasts from great apes, Homo erectus, Homo sapiens, a human pygmy, a human microcephalic, specimen number Sts 5 (Australopithecus africanus), and specimen number WT 17000 (Paranthropus aethiopicus). Morphometric, allometric, and shape data indicate that LB1 is not a microcephalic or pygmy. LB1's brain/body size ratio scales like that of an australopithecine, but its endocast shape resembles that of Homo erectus. LB1 has derived frontal and temporal lobes and a lunate sulcus in a derived position, which are consistent with capabilities for higher cognitive processing.

Geometric morphometrics and paleoneurology: brain shape evolution in the genus Homo

Paleoneurology concerns the study and analysis of fossil endocasts. Together with cranial capacity and discrete anatomical features, shape can be analysed to consider the spatial relationships between structures and to investigate the endocranial structural system. A sample of endocasts from fossil specimens of the genus Homo has been analysed using traditional metrics and 2D geometric morphometrics based on lateral projections of endocranial shape. The maximum and frontal widths show a size-related pattern of variation shared by all the taxa considered. Furthermore, as cranial capacity increases in the non-modern morphotypes there is a general endocranial vertical stretching (mainly centred at the anterior ascending circumvolution) with flattening and relative shortening of the parietal areas. This pattern could have involved some structural stress between brain development and vault bones at the parietal midsagittal profile in the heavy encephalised Neandertals. In contrast, modern humans show a species-specific neomorphic hypertrophy of the parietal volumes, leading to a dorsal growth and ventral flexion (convolution) and consequent globularity of the whole structure. Brain tensors such as the falx cerebri have been hypothesised to represent one of the main physical constraints on morphogenetic trajectories, with additional influences from cranial base structures. The neurofunctional inferences discussed here stress the role of the parietal areas in the visuo-spatial coordination and integration, which can be involved in higher cerebral functions and related to conceptual thinking.

The taxonomic status of the Chemeron temporal (KNM-BC 1)

Temporal bone morphology, as part of the basicranium, is commonly used in systematic evaluation of early hominid fossils. When an isolated right temporal bone, KNM-BC 1 (the Chemeron temporal) was discovered in the Baringo Basin, Kenya, Tobias (1967 a, Nature215, 476-480), citing ambiguity of characters, hesitated to place the specimen generically, attributing the fossil only to Hominidae gen. et sp. indet. Since that discovery, the early hominid sample has grown considerably and comparisons with this expanded dataset led Hill et al. (1992 a, Nature355, 719-722) to revise the placement of KNM-BC 1 including it within the genus Homo. This revision was possible due to the increased number of hominid fossil specimens from the late Pliocene/early Pleistocene, most notably members of the genus Homo. A thorough investigation into the utility of the temporal bone in hominid systematics shows that many features, as currently used in the literature, demonstrate high levels of variation thus questioning their phyletic valence. It is shown, however, that the temporal bone still contains useful systematic information. A detailed anatomical description of KNM-BC 1 is provided and, when discussed in the context of temporal bone features provided, affirms the conclusion of Hill et al. (1992 a) and places the fossil within the genus Homo.

Morphological differences between minicolumns in human and nonhuman primate cortex

Our study performed a quantitative investigation of minicolumns in the planum temporale (PT) of human, chimpanzee, and rhesus monkey brains. This analysis distinguished minicolumns in the human cortex from those of the other nonhuman primates. Human cell columns are larger, contain more neuropil space, and pack more cells into the core area of the column than those of the other primates tested. Because the minicolumn is a basic anatomical and functional unit of the cortex, this strong evidence showed reorganization in this area of the human brain. The relationship between the minicolumn and cortical volume is also discussed.

A quantitative and qualitative reanalysis of the endocast from the juvenile Paranthropus specimen l338y-6 from Omo, Ethiopia

Based on an analysis of its endocast, Holloway (1981 Am J Phys Anthropol 53:109-118) attributed the juvenile Omo L338y-6 specimen to Australopithecus africanus (i.e., gracile australopithecines) rather than to Paranthropus (Australopithecus) boisei (robust australopithecines) favored by other workers (Rak and Howell [1978] Am J Phys Anthropol 48:345-366). Holloway's attribution was based on the specimen's (1) low cranial capacity, (2) gracile-like meningeal vessels, (3) gracile-like cerebellar hemispheres, and (4) absence of an enlarged occipital/marginal (O/M) sinus system. Recent work, however, has shown that criteria 1 and 2 are not useful for sorting gracile from robust australopithecines (Culotta [1999] Science 284:1109-1111; Falk [1993] Am J Phys Anthropol 92:81-98). In this paper, we test criterion 3 by quantifying the endocranial cerebellar and occipital morphology reproduced on the Omo L338y-6 endocast, and comparing it to seven endocasts from South and East African early hominids. Our preliminary results show that metric analysis of this specimen cannot be used to sort it preferentially with either robust or gracile australopithecines. Finally, we demonstrate that, contrary to previous reports, the Omo L338y-6 endocast reproduces an enlarged left occipital sinus (criterion 4). This observation is consistent with the original attribution of the Omo specimen to robust australopithecines (Rak and Howell [1978] Am J Phys Anthropol 48:345-366). Furthermore, if Omo L338y-6 was a robust australopithecine, this discovery extends the occurrence of an enlarged O/M sinus system to one of the earliest known paranthropines. Am J Phys Anthropol 110:399-406, 1999.

The posterior border of the sphenoid greater wing and its phylogenetic usefulness in human evolution

The elucidation of patterns of cranial skeletal maturation and growth in fossil hominids is possible not only through dental studies but also by mapping different aspects of ossification in both extant African apes and humans. However, knowledge of normal skeletal development in large samples of extant great apes is flimsy. To remedy this situation, this paper offers an extensive survey and thorough discussion of the ossification of the posterior border of the sphenoid greater wing. Indeed, this area provides much information about basicranial skeletal maturation. We investigate three variants: the absence of the foramen spinosum and the position of both the foramen spinosum and the foramen ovale in relation to the sphenosquamosal suture. Providing original data about humans and 1,425 extant great ape skulls and using a sample of 64 fossil hominids, this study aimed to test whether different ossification patterns occurred during the course of human evolution. The incidence of three derived morphologies located on the posterior border of the sphenoid greater wing increases during human evolution at different geological periods. The evolutionary polarity of these three derived morphologies is assessed by outgroup comparison and ontogenetic methods. During human evolution, there is a clear trend for the foramen spinosum to be present and wholly located on the posterior area of the sphenoid greater wing. Moreover, in all the great ape species and in Australopithecus afarensis, the sphenosquamosal suture may split the foramen ovale. Inversely, the foramen ovale always lies wholly within the sphenoid greater wing in Australopithecus africanus, robust australopithecines, early Homo, H. erectus (and/or H. ergaster), and Homo sapiens. From ontogenetic studies in humans, we conclude that, during human evolution, the ossification of the posterior area of the sphenoid greater wing progressively surrounded the middle meningeal artery (passing through the foramen spinosum) and the small meningeal artery (passing through the foramen ovale).

Lateralized changes in tympanic membrane temperature in relation to different cognitive tasks in chimpanzees (Pan troglodytes)

Lateralized changes in tympanic membrane (TM) temperature were assessed in chimpanzees. Subjects were engaged in 1 of 3 different cognitive tasks, including matching-to-sample, visual-spatial discrimination, and a motor task. During execution of each task, TM temperatures were taken from each ear over a 20-min time period. The TM temperatures at each time interval were subtracted from a baseline measure to assess relative change in blood flow. For the matching-to-sample and visual-spatial discrimination tasks, significant lateralized changes in TM temperature were found, with left-ear temperature increasing and right-ear temperature decreasing. No laterality effects were found for the motor or control tasks. These data provide the first evidence of laterality in physiological functioning in chimpanzees and suggest that transient asymmetries in cognitive functions are associated with changes in cerebral blood flow as assessed by TM temperature change.

Further data about venous channels in South African Plio-Pleistocene hominids

Original data about venous channels in South African Plio-Pleistocene hominids are discussed. To assess possible changes in blood volume flow of fossil hominids, we test whether dimensions of three extracranial venous foramina were different between Australopithecus africanus and Australopithecus (Paranthropus) robustus. Moreover, providing further data about the small sample of South African Plio-Pleistocene hominids, we also attempt to re-analyse the incidence of divided hypoglossal canals and four emissary foramina in a very large sample of extant African apes representing all ages, species and subspecies, in A. africanus and in "robust australopithecines". Up to now, only very poor data on extracranial dimensions of venous foramina were available for fossil hominids. However, this topic provides interesting information about the modifications of volume flow during human evolution. Assuming that in fossil hominids, as in humans, dimensions of condylar and mastoid foramina, as well as those of jugular foramina, depended on volume flow through them, we conclude, first, that volume flow through internal jugular veins was comparable in South African australopithecines, extant chimpanzees and humans, and second, that, in comparison with the extant less-encephalized chimpanzees (presumably reflecting the ancestral condition), volume flow was higher through condylar veins in A. (P.) robustus. This increase was responsible for a significantly greater amount of blood drainage from the brain (and consequently an increased arterial blood supply). We support the view that encephalization was the prevailing functional explanation for volume flow increase through condylar veins in A. (P.) robustus, in comparison with its ancestor with its presumably more ape-like degree of encephalization. Considering the incidence of emissary canals and foramina, significant differences between A. africanus, "robust australopithecines" and all the extant African ape species, were tested statistically. Concerning the condylar canal, we did not find differences between "robust australopithecines" and extant African apes. Concerning the incidence of divided hypoglossal canals, mastoid canals, parietal and occipital foramina, no difference was found between extant African apes, A. africanus and "robust australopithecines". High frequencies of either condylar or mastoid canals cannot be regarded as a "pongid condition". Moreover, we did not find convincing data to support the hypothesis that mastoid emissary veins (partly representing a putative "radiator" for cooling the brain) were selected in A. africanus, in comparison with "robust australopithecines".

Comparative endocranial vascular changes due to craniosynostosis and artificial cranial deformation

The processes of craniosynostosis (premature fusion of one or more of the calvarial sutures) and artificial cranial deformation are similar since both can alter the shape of the craniofacial complex. Most research exploring these processes has focused on the ectocranium, although it is obvious that these processes also modify the endocranium. Endocranial changes due to either craniosynostosis or artificial cranial deformation have not been as thoroughly examined. Silicone rubber endocasts were made from 11 craniosynostotic archaeologically derived specimens from North and South America. For comparative purposes, endocasts were made from 22 normal and 17 occipitally deformed crania that were archaeologically derived from North and South America. With all samples, middle meningeal vessel patterns and venous sinus impressions were qualitatively and quantitatively analyzed. Depth, width, and convolution of the middle meningeal vessels were recorded, and the direction of vessel branches was noted. Both artificial cranial deformation and craniosynostosis altered the endocranial vasculature. Middle meningeal vessel and venous sinus impressions of the craniosynostotic group differed when compared to both the undeformed and artificially cranially deformed samples. Sinuses traversing under synostosed sutures became wider and deeper. In contrast, sinuses directly underneath the greatest artificial deformational stress were shallower, while there was compensatory enlargement of sinuses further away from the greatest deformational effects. Such compensatory enlargement also was shown by the high incidence of enlarged occipital/marginal sinuses in artificially deformed skulls. Increased intracranial pressure is hypothesized to be the cause of the venous sinus changes found in craniosynostotic individuals. Middle meningeal vessel patterns from craniosynostotic and artificially deformed specimens were similar in that their direction paralleled the direction of altered cranial growth. These findings demonstrate that the endocranial vasculature is developmentally plastic and responds to deformation in a predictable pattern.