Where does the cranial base flexion take place in humans?

The modern human has the most flexed cranial base among all living animals. The flexure allowed a larger cranial volume to accommodate a greater brain. Spheno-occipitalis synchondrosis (SOS) has been largely responsible for cranial base flexion, between the sphenoid and the Pars basilaris of the occipital bone. The objective of this work is to evaluate the real place of skull base flexure. Analysis based on 50 magnetic resonance imaging from normal adult subjects were used to evaluate normal place for cranial base angulation (CBA). The vertex of the cranial base angle in all individuals occurred intrinsically in the sphenoid bone. In humans, cranial base flexure had a specific pre-chordal origin, rather than in the transition between pre-chordal and chordal plates and occurred in the inner sphenoidal bone.

A comprehensive review of the clivus: anatomy, embryology, variants, pathology, and surgical approaches.

INTRODUCTION: The clivus is a bony structure formed by the fusion of the basioccipital and basispheniod bone at the sphenooccipital synchondrosis. This downward sloping structure from the dorsum sellae to the foramen magnum is derived from mesoderm and ectoderm properties. METHODS: This comprehensive review of the clivus will discuss its basic anatomy, embryology, pathological findings, and surgical implications. The clivus is an endochondral bone, formed under two processes; first, a cartilaginous base is developed, and it is secondly reabsorbed and replaced with bone. Knowledge of its embryological structure and growth of development will clarify the pathogenesis of anatomical variants and pathological findings of the clivus. CONCLUSIONS: Understanding the anatomy including proximity to anatomical structures, adjacent neurovasculature properties, and anatomical variants will aid neurosurgeons in their surgical management when treating pathological findings around the clivus.

Embryonic development of the skull of the Andean lizard Ptychoglossus bicolor (Squamata, Gymnophthalmidae).

The study of cranial design and development in Gymnophthalmidae is important to understand the ontogenetic processes behind the morphological diversity of the group and to examine the possible effects of microhabitat use and other ecological parameters, as well as phylogenetic constraints, on skull anatomy. Complete morphological descriptions of embryonic skull development within Gymnophthalmidae are non-existent. Likewise, very little is known about the complete chondrocranium of the family. Herein, the development of the skull of the semi-fossorial lizard Ptychoglossus bicolor is described along with an examination of the chondrocranium of other gymnophthalmid taxa and the teiid Cnemidophorus lemniscatus. Cranial chondrification begins with early condensations in the ethmoid, orbitotemporal and occipital regions of the chondrocranium as well as the viscerocranium. Ossification of the skull starts with elements of the dermatocranium (pterygoid, prefrontal, maxilla and jugal). The orbitosphenoid is the last chondral bone to appear. At birth, the skull is almost completely ossified and exhibits a large frontoparietal fontanelle. In general terms, the chondrocranium of the gymnophthalmids studied is characteristic of lacertiform terrestrial lizards, in spite of their life habits, and resembles the chondrocranium of C. lemniscatus in many aspects. However, the gymnophthalmids show great variation in the orbitosphenoid and a complex nasal capsule. The latter exhibits greater development of some nasal cartilages, which make it more complex than in C. lemniscatus. These characteristics might be related to microhabitat use and the well-developed olfactory and vomeronasal systems observed within this clade.

Frecuencia del hueso interparietal o incaico en cráneos atácamenos (Lican antai) prehispánicos del norte de Chile / Frequency of interparietal bone or inca bone in pre-hispanic Atacamenos (Lican Antai) skulls of the north of Chile

El hueso interparietal se considera un hueso intercalar originado de centros independientes de osificación y rodeado por sus propias suturas. Se encontró en fósiles homínidos y humanos tempranos. Se cree que el occipucio sufre transformaciones por mutaciones al iniciarse la evolución humana reforzando esta teoría las variaciones suturales que presenta el occipital. Sería un rasgo genéticamente dominante, propuesta ratificada por estudios experimentales. Se observa con variadas formas según la fusión de los núcleos de osificación, por lo que todos los huesos ubicados en la zona de la escama del occipital no se pueden clasificar como suturales o wormianos y deben considerarse como parte del hueso interparietal. Tratando de confirmar la alta frecuencia obtenida en investigaciones anteriores realizadas en cráneos de individuos originarios del norte de Chile, se analizaron 83 cráneos de atacamenos prehispánicos de ambos sexos, seleccionados al azar entre 293 individuos exhumados del cementerio Coyo-Oriente, datados entre 300-1200 D.C período post-Tiwanaku y que forman parte del Museo R.P. Gustavo Le Paige en San Pedro de Atacama, dependiente del Instituto de Investigaciones Arqueológicas de la Universidad Católica del Norte, que fueron fotografiados en todas sus normas anatómicas y que se midieron paras obtener el índice craneal o cefálico. El hueso interparietal está presente en 23 de 83 cráneos, con una frecuencia de 27,71 por ciento, sin diferencias estadísticas significativas al 95 por ciento con investigaciones realizadas en cráneos de origen étnico similar y en otras etnias que presentan alta frecuencia de hueso interparietal. Por el contrario, se encontraron diferencias estadísticamente significativas al 95 por ciento con frecuencias determinadas en cráneos europeos caucásicos y euroasiáticos. Los autores integraron las tablas clasificatorias de Kadanoff y Hanihara-Ishida, para obtener una tabla modificada que permitiera clasificar ...

The interparietal bone is considered an intercalary bone originated by independent ossification centers and surrounded by its own sutures. It is found in early hominids and human fossils. It is believed that the occipital bone undergoes transformations by mutations at the beginning of human evolution. Reinforcing this theory are the suture variations that presents the occipital bone. It would be a dominant genetic characteristic, proposal ratified by experimental studies. It is observed with varied forms according to the fusion of the ossification nuclei; reason why all the bones located in the zone of the occipital flake cannot be classified as sutures or wormians and must be considered part of the interparietal bone. Trying to confirm the high frequency obtained in previous investigations realized in skulls of original individuals of the north of Chile, we analyzed 83 skulls of pre-Hispanic atácamenos (lican antai) of both sexes, selected at random between 293 individuals of the Coyo-Orient cementery, dated between 300-1200 A.C, post-Tiwanaku period and these remains are part of R.P Gustavo Le Paige's Museum in San Pedro de Atacama, which is part of the Institute of Archaeological Investigations of the North Catholic University. The remains were photographed in all anatomical norms and that were measured to obtain the cranial or cephalic Index. The interparietal bone is present in 23 of 83 skulls, with a frequency of 27.71 percent, without significant statistical differences to 95 percent with investigations realized in skulls of similar ethnic origin and other ethnic groups who present high frequency of interparietal bone. On the contrary, statistically significant differences to 95 percent were found with frequencies determined in caucasian and euroasiatics european skulls. The authors integrated the classificatory tables of Kadanoff and Hanihara-Ishida, to obtain a modified table that allowed to classify all the found variations ...