Neurocranial Volume Research Articles

Skull Shape Variations in the Eidolon helvum (African Fruit Bat) Based on Geographical Location.

The shape and size of a skull provides insight into the age, breed and gender of the animal. Skull shape variations have been reported in different animals, with some theories linking these variations to evolution and/or migration. This study assessed the variations observed in the skull shape, size and gross morphometrics of two groups of the Eidolon helvum obtained from two geographical regions in Nigeria (south and north). All skulls were rostro-caudally elongated, having a dolichocephalic appearance. The skulls from the north had a distinct dome shape, with a more prominent zygomatic process, absence of a 'diastema' and an extra upper molar, while the southern skulls showed a more dorsally flattened skull and a less prominent zygomatic process. The shape of the sagittal crest was different in the two groups, while there was the presence of an accessory infraorbital foramen in some of the southern skulls. The southern skulls lacked the palatine foramen. The lacrimal foramen was observed to be more caudally placed in the southern skulls. Values for most linear measurements were higher in the northern skulls, although statistically significant difference was not present in all. The value for the neurocranial volume was considerably higher in the northern skulls (4.41 ± 0.28 mls) relative to the southern skulls (2.0 ± 0.27 mls). Statistically significant differences were not observed between males and females (within regions). Data obtained from this study may find application in evolution and migration studies, wildlife medicine and surgery and comparative and forensic anatomy.

Morphometric investigation of neurocranium in domestic cat (Felis catus)

This study was intended to investigate some aspects of the morphometric characteristics of the neurocranium in domestic cat (Felis catus) of Bangladesh. Twenty adult domestic cat including 10 males and 10 female were euthanized using diazepam (@ 20 mg/kg) and their skulls were macerated to give morphometric parameters. Student t-test with level of significance set at 5% (p < 0.05) was used to analyze the obtained values. The mean (mean ± SE) neurocranial volume was 28 ± 0.97 ml, neurocranial length was 6.63 ± 0.77 cm, and the neurocranial height and index were 3.32 ± 0.38 cm and 49.83%, respectively. The mean height and width of the foramen magnum were 1.32 ± 0.09 cm and 1.35 ± 0.08 cm, respectively, while the foramen index was below 100 at 90.72 ± 4.93. Parameters for the foramen magnum index showed significant difference between both sexes at p < 0.05. The foramen magnum showed shape variations and there were multiple hypoglossal foramina in over 80% of the cats. Foramen magnum index was positively correlated with neurocranial volume. The results were discussed in terms of the usage of morphologic and morphometric characteristics of cranium and skulls in several basic and clinical applications in cat such as estimation of the brain density and the use of the cat for cranial pressure experiments. DOI: http://dx.doi.org/10.3329/bjvm.v11i1.17302 Bangl. J. Vet. Med. (2013). 11 (1): 69-73

Clustering of the cephalofacial measurements

The purpose of this study was to study the latent structure of the cephalofacial variables and to explain the clustering of these measurements. Eleven cephalofacial measurements were done on 561 male entities aged 18-35 years. The collected data are analysed through descriptive parameters, correlation analysis, and factorial analyses. Correlation analysis confirms three sets of variables that realise the higher correlations with each other. According to the principal component analysis of the factor analysis three latent factors have been extracted that explain 53.3% of the total variance: the neurocranial volume factor; the transversal factor of the face; and the longitudinal factor of the face. The reduction of multiple measured manifest variables in a small number of latent factors may facilitate the work of anthropologists in studying and explaining of the genetic basis of development of bones, cartilages and soft tissues of the head and their morphological construction.

Neurometry and Neurocraniometry of the Nigerian Local Dog (Canis lupus familiaris)

This study investigates the linear morphometry of the brain and the neurocranium which houses it, in the Nigerian local dog. A total of twenty-five dogs (11 males, 14 females) were used for this study. The males recorded a heavier body weight, weight of head and brain. The females recorded higher values for the length of brain, height and length of cerebellum, and the whole skull height and length relative to the males, although no statistically significant differences were observed (P>0.05). Values obtained for the neurocranial volume was similar between the sexes, while the neurocranial height and length was higher in the males, even though no statistically significant differenceswere observed (P>0.05). Pearson‟scorrelation analysis showed a negative correlation between the weight of the animal and length of brain and the height and length of cerebellum, showing that values for these parameters were likely to relatively higher in younger animals. This study shows correlation relationship between neurometric and neurocraniometric parameters, data obtained may find application in veterinary clinical neuroanatomy of dolichocephalic-type dogs.

Growth of functional cranial components in rats with intrauterine growth retardation after treatment with growth hormone

The goal of this study was to analyse the effect of growth hormone (GH) on catch-up growth of functional facial (splanchnocranial) and neurocranial components in rats with intrauterine growth retardation (IUGR). Wistar rats were divided into the following groups: control (C), sham-operated (SH), IUGR, and IUGR + GH. IUGR was surgically induced and GH was administered between 21 and 60 days of age. Radiographs were obtained at 1, 21, 42, 63, and 84 days of age in order to measure length, width, and height of neurocranium (NL, NW, and NH) and face length, width, and height (FL, FW, and FH). Analysis of variance was performed at 1 day of age and a principal components analysis (PCA) at 84 days of age. Neurocranial and facial volumetric indexes were calculated as NVI = (3)√NL × NW × NH and FVI = (3)√FL × FW × FH, respectively, and adjusted by non-linear regression analysis. On postnatal day 1, there were significant differences between SH and IUGR (P < 0.01). Also, in both genders, final neurocranial volume was similar between SH and IUGR + GH groups, while the IUGR group had the lower value (P < 0.01). Final facial volume was similar among the three groups. In both genders, facial growth rates were SH = IUGR > IUGR + GH (P < 0.01). The first axis of the PCA exhibited size effect and the second axis showed shape effect. Reductions of placental blood flow modify cranial growth. The functional neurocranial and facial components in rats with IUGR presented different recovery strategies through modular behaviour, mainly related to modifications of growth rate as response to GH administration.

Primate cranial diversity

Many studies in primate and human evolution focus on aspects of cranial morphology to address issues of systematics, phylogeny, and functional anatomy. However, broad analyses of cranial diversity within Primates as an Order are notably absent. In this study, we present a 3D geometric morphometric analysis of primate cranial morphology, providing a multivariate comparison of the major patterns of cranial shape change during primate evolution and quantitative assessments of cranial diversity among different clades. We digitized a set of 18 landmarks designed to capture overall cranial shape on male and female crania representing 66 genera of living primates. The landmark data were aligned using a Generalized Procrustes Analysis and then subjected to a principal components analysis to identify the major axes of cranial variation. Cranial diversity among clades was compared using multivariate measurements of variance. The first principal component axis reflects differences in cranial flexion, orbit size and orientation, and relative neurocranial volume. In general, it separates strepsirrhines from anthropoids. The second axis reflects differences in relative cranial height and snout length and primarily describes differences among anthropoids. Eulemur, Mandrillus, Pongo, and Homo are among the extremes in cranial shape. Anthropoids, catarrhines, and haplorhines show a higher variance than prosimians or strepsirrhines. Hominoids show the highest variance in cranial shape among extant primate clades, and much of this diversity is driven by the unique cranium of Homo sapiens.

Estimation of cranial capacity and brain weight in 18–22-year-old Iranian adults

Objective Cranial capacity, brain weight and cerebral index are important measurements in the study of racial differences. Clinically, an analysis of cranial capacity and weight exposes another aspect of growth and development and permits critical evaluation of unusually large, small, or misshapen crania. Subjects and methods Brain weight and cerebral index were estimated in 772 normal 18–22-year-old (320 males, 452 females) Iranian people of different socioeconomic groups, using linear dimensions of the head (using Lee–Pearson's formula) measured with spreading caliper and auricular head spanner. Results Cranial capacity, brain weight and cerebral index in males were 1343.45 ± 102.37 cm 3 (mean ± S.D.), 1390.47 ± 105.95 g, and 2.17 ± 0.27% respectively. Cranial capacity, brain weight and cerebral index in females were 1163.02 ± 115.76 cm 3, 1203.73 ± 119.81 g, and 2.25 ± 0.31% respectively. Conclusion It was shown that neurocranial volume and weight of male is higher than female. Also, the results are different from previous studies in Western countries which may be a result of racial, topodemic, and socioeconomic variations. Finally, we propose the new “cerebral quotient” for anthropometric measurements.

Ontogenetic allometry, heterochrony, and interspecific differences in the skull of African apes, using tridimensional Procrustes analysis.

Ontogenetic studies of African ape skulls lead to an analysis of morphological differences in terms of allometry, heterochrony, and sexual dimorphism. The use of geometric morphometrics allows us 1) to define size and shape variations as independent factors (an essential but seldom respected condition for heterochrony), and 2) to calculate in percentage of shape changes and to graphically represent the parts of shape variation which are related to various biological phenomena: common allometry, intraspecific allometry, and allometric and nonallometric shape discrimination. Three tridimensional Procrustes analyses and the calculation of multivariate allometries, discriminant functions, and statistical tests are used to compare the skulls of 50 Pan troglodytes, and 50 Gorilla gorilla of different dental stages. The results both complement and modify classical results obtained from similar material but with different methods. Size and Scaling in Primate Morphology, New York: Plenum, p. 175-205). As previously described by Shea, the common growth allometric pattern is very important (64% of total shape variation). It corresponds to a larger increase of facial volume than of neurocranial volume, a more obliquely oriented foramen magnum, and a noticeable reshaping of the nuchal region (higher inion). However, the heterochronic interpretation based on common allometry is rather different from Shea. Gorillas differ from chimpanzees not only with a larger magnitude of allometric change (rate peramorphosis), as is classically said, but also grow more in size than in shape (size acceleration). In other words, for a similar stage of growth, gorillas have the size and shape corresponding to older chimpanzees, and for a similar shape, gorillas have a larger size than chimpanzees. In contrast, sexual dimorphism actually corresponds to allometric changes only, as classically demonstrated (time hypermorphosis). Sexual dimorphism is here significant in adult gorillas alone, and solely in terms of allometry (size-related shape and size, given that sagittal and nuchal crests are not taken into account). The study also permits us to differentiate two different shape variations that are classically confused in ontogenetic studies: a very small part of allometric shape change which is specific to each species (1% of the total shape variation), and nonallometric species-specific traits independent of growth (8% of total shape change). When calculated in terms of intraspecific allometries (including common allometry and noncommon allometry), shape changes are more extensive in gorillas (36% of total shape change) than in chimpanzees (29% of total shape change). The allometric differences mainly concern the inion, which becomes higher; the position of the foramen magnum, more dorsally oriented; and the palate, more tilted in adult gorillas than in adult chimpanzees. In contrast, nonallometric species-specific traits in gorillas are the long and flat vault characterized by a prominent occipital region, the higher and displaced backward glabella, and the protrusive nose. Biomechanical schemes built from shape partition suggest that the increased out-of-plumb position of the head during growth is partially compensated in gorillas by a powerful nuchal musculature due to the peculiar shape of the occipital region.

Craniofacial growth of immature rats following administration of vincristine and doxorubicin.

The aim of the present study was to investigate the possible short-term effect of two anti-neoplastic drugs, vincristine and doxorubicin, on the craniofacial skeleton in young rats. On the basis of findings from pilot experiments, one dose of 0.0375 mg/kg vincristine or 1.0 mg/kg doxorubicin was given parenterally to inbred Long-Evans/Turku rats at 10 or 30 days of age, and followed up until 30 or 50 days, respectively. Some 30-day-old rats received two additional doses of the drugs, 3 and 6 days after the first injection. Controls were given physiological saline. A total of 310 rats were used: 40 for the pilot study, 180 medicated, and 90 control animals for the experiment itself. The weights of the rats were recorded, a number of craniofacial dimensions were measured, and the neurocranial volume determined in the case of the most severely affected rats. The weight gain of the younger rats was retarded, as was that of the older rats that received repeated drug injections. Most dimensions of the craniofacial skeleton were significantly smaller in the vincristine-treated young animals, and following multiple injections of vincristine or doxorubicin also in the older ones when compared with the controls. Contrary to the general pattern, the measurements of the foramen magnum increased in the older rats, a feature associated with the decrease in brain cavity volume observed in those that received vincristine. These findings indicate that anti-neoplastic agents can have a short-term adverse effect on the craniofacial growth and that the morphological changes are differential, rather than uniform.

Basicranial flexion, relative brain size, and facial kyphosis in Homo sapiens and some fossil hominids

Comparative work among nonhominid primates has demonstrated that the basicranium becomes more flexed with increasing brain size relative to basicranial length and as the upper and lower face become more ventrally deflected (Ross and Ravosa [1993] Am. J. Phys. Anthropol. 91:305-324). In order to determine whether modern humans and fossil hominids follow these trends, the cranial base angle (measure of basicranial flexion), angle of facial kyphosis, and angle of orbital axis orientation were measured from computed tomography (CT) scans of fossil hominids (Sts 5, MLD 37/38, OH9, Kabwe) and lateral radiographs of 99 extant humans. Brain size relative to basicranial length was calculated from measures of neurocranial volume and basicranial length taken from original skulls, radiographs, CT scans, and the literature. Results of bivariate correlation analyses revealed that among modern humans basicranial flexion and brain size/basicranial length are not significantly correlated, nor are the angles of orbital axis orientation and facial kyphosis. However, basicranial flexion and orbit orientation are significantly positively correlated among the humans sampled, as are basicranial flexion and the angle of facial kyphosis. Relative to the comparative sample from Ross and Ravosa (1993), all hominids have more flexed basicrania than other primates: Archaic Homo sapiens, Homo erectus, and Australopithecus africanus do not differ significantly from Modern Homo sapiens in their degree of basicranial flexion, although they differ widely in their relative brain size. Comparison of the hominid values with those predicted by the nonhominid reduced major-axis equations reveal that, for their brain size/basicranial length, Archaic and Modern Homo sapiens have less flexed basicrania than predicted. H. erectus and A. africanus have the degree of basicranial flexion predicted by the nonhominid reduced major-axis equation. Modern humans have more ventrally deflected orbits than all other primates and, for their degree of basicranial flexion, have more ventrally deflected orbits than predicted by the regression equations for hominoids. All hominoids have more ventrally deflected orbital axes relative to their palate orientation than other primates. It is argued that hominids do not strictly obey the trend for basicranial flexion to increase with increasing relative brain size because of constraints on the amount of flexion that do not allow it to decrease much below 90 degrees. Therefore, if basicranial flexion is a mechanism for accommodating an expanding brain among non-hominid primates, other mechanisms must be at work among hominids.

Basicranial flexion, relative brain size, and facial kyphosis in nonhuman primates.

Numerous hypotheses explaining interspecific differences in the degree of basicranial flexion have been presented. Several authors have argued that an increase in relative brain size results in a spatial packing problem that is resolved by flexing the basicranium. Others attribute differences in the degree of basicranial flexion to different postural behaviors, suggesting that more orthograde animals require a ventrally flexed pre-sella basicranium in order to maintain the eyes in a correct forward-facing orientation. Less specific claims are made for a relationship between the degree of basicranial flexion and facial orientation. In order to evaluate these hypotheses, the degree of basicranial flexion (cranial base angle), palate orientation, and orbital axis orientation were measured from lateral radiographs of 68 primate species and combined with linear and volumetric measures as well as data on the size of the neocortex and telencephalon. Bivariate correlation and partial correlation analyses at several taxonomic levels revealed that, within haplorhines, the cranial base angle decreases with increasing neurocranial volume relative to basicranial length and is positively correlated with angles of facial kyphosis and orbital axis orientation. Strepsirhines show no significant correlations between the cranial base angle and any of the variables examined. It is argued that prior orbital approximation in the ancestral haplorhine integrated the medial orbital walls and pre-sella basicranium into a single structural network such that changes in the orientation of one necessarily affect the other. Gould's ("Ontogeny and Phylogeny." Cambridge: Belknap Press, 1977) hypothesis, that the highly flexed basicranium of Homo may be due to a combination of a large brain and a relatively short basicranium, is corroborated.

The ontogeny of cranial sexual dimorphism in two old world monkeys:Macaca fascicularis (Cercopithecinae) andNasalis larvatus (Colobinae)

Allometric and heterochronic approaches to sexual dimorphism have contributed much to our understanding of the evolutionary morphology of the primate skull and dentition. To date, however, extensive studies of sexual dimorphism have been carried out only on the great apes and a few cercopithecine monkeys. To fill this gap, representative dimensions of the skull were collected among ontogenetic series of two dimorphic Old World monkeys:Macaca fascicularis (Cercopithecinae) andNasalis larvatus (Colobinae). The ontogeny of cranial sexual dimorphism was evaluated with least-squares bivariate regression, analysis of covariance (ANCOVA), and analysis of variance (ANOVA). Results indicate that within each species the sexes typically exhibit nonsignificant differences in ANCOVAs of ontogenetic trajectories, except for bivariate comparisons with bicanine breadth. AmongMacaca fascicularis, ANOVAs between males and females of common dental ages show that adult, and frequently subadult, males are significantly larger than females, i.e., sexual dimorphism develops via time and rate hypermorphosis (males primarily grow for a longer time period as well as faster). AmongNasalis larvatus, however, comparisons between males and females of common dental ages indicate that only adult males are significantly larger than females, i.e., sexual dimorphism develops primarily via time hypermorphosis (males grow for a longer time period). Within both species, females appear to exhibit an early growth spurt at dental age 2; that is, many cranial measures for females tend to be larger than those for males. Measures of the circumorbital region (e.g., browridge height), body weight, and bicanine breadth exhibit typically the highest sexual dimorphism ratios. The fact that postcanine toothrow length and neurocranial volume (less so inNasalis) demonstrate very low dimorphism ratios generally supports assertions that postnatal systemic growth (and associated selective pressures thereon) exerts a greater influence on facial, but not neural, dental, or orbital, development (Cochard, 1985, 1987; Shea, 1985a,b, 1986; Shea and Gomez, 1988; Sheaet al., 1990). Additional consideration of ontogenetic differences between species generally supports previous functional interpretations of subfamilial differences in cranial form related to agonistic displays in cercopithecine monkeys (Ravosa, 1990).