Craniodental anatomy in Permian-Jurassic Cynodontia and Mammaliaformes (Synapsida, Therapsida) as a gateway to defining mammalian soft tissue and behavioural traits.

Mammals are diagnosed by more than 30 osteological characters (e.g. squamosal-dentary jaw joint, three inner ear ossicles, etc.) that are readily preserved in the fossil record. However, it is the suite of physiological, soft tissue and behavioural characters (e.g. endothermy, hair, lactation, isocortex and parental care), the evolutionary origins of which have eluded scholars for decades, that most prominently distinguishes living mammals from other amniotes. Here, we review recent works that illustrate how evolutionary changes concentrated in the cranial and dental morphology of mammalian ancestors, the Permian-Jurassic Cynodontia and Mammaliaformes, can potentially be used to document the origin of some of the most crucial defining features of mammals. We discuss how these soft tissue and behavioural traits are highly integrated, and how their evolution is intermingled with that of craniodental traits, thus enabling the tracing of their previously out-of-reach phylogenetic history. Most of these osteological and dental proxies, such as the maxillary canal, bony labyrinth and dental replacement only recently became more easily accessible-thanks, in large part, to the widespread use of X-ray microtomography scanning in palaeontology-because they are linked to internal cranial characters. This article is part of the theme issue 'The mammalian skull: development, structure and function'.

Comparison between the parietal foramina observed in samples of African and European population groups / Comparación entre los forámenes parietales observados en muestras de grupos de población africanos y europeos

SUMMARY: Parietal foramina of the human skull act as a passageway for emissary veins, connecting the superior sagittal sinus to the veins of the scalp. This passageway can lead to the spread of infection from the scalp to the dural venous sinuses, but may also assist in relieving intracranial pressure. However, variation in the prevalence of parietal foramina has been noted among population groups. This observational and descriptive study aimed to determine the incidence, size and location of parietal foramina by using osteological specimens of 252 African skulls from the Sefako Makgatho Health Sciences University, South Africa and 95 European skulls from the University of Leipzig, Germany. Parietal foramina were significantly more common in the African sample (61.9 %) compared to the European sample (55.8 %). Moreover, the Central European sample displayed more unilateral foramina (29.5 %), while the African sample exhibited more bilateral foramina (40.8 %). The diameter of the parietal foramen average 1.98 mm and 1.88 mm for the European and African samples, respectively. In this study, a median foramen on the sagittal suture was observed in 14 of the overall skull caps (4 %). This study demonstrated that parietal foramina are more prevalent than anticipated in both population groups. Findings of this study, indicating an increased prevalence, and the subsequent possibility of more emissary veins encountered, can be used to improve the understanding of the variations in the prevalence and clinical implications of the parietal foramen among various population groups located world-wide.

Los forámenes parietales del cráneo humano actúan como una vía para las venas emisarias, conectando el seno sagital superior con las venas del cuero cabelludo. Este pasaje puede conducir a la propagación de infecciones desde el epicráneo (calva) hasta los senos venosos durales, pero también puede ayudar a aliviar la presión intracraneal. Sin embargo, se ha observado una variación en la prevalencia de los forámenes parietales entre los grupos de población. Este estudio observacional y descriptivo tuvo como objetivo determinar la incidencia, el tamaño y la ubicación de los forámenes parietales mediante el uso de muestras osteológicas de 252 cráneos africanos de la Universidad de Ciencias de la Salud Sefako Makgatho, Sudáfrica, y 95 cráneos europeos de la Universidad de Leipzig, Alemania. Los forámenes parietales fueron significativamente más comunes en la muestra africana (61,9 %) en comparación con la muestra europea (55,8 %). Además, la muestra centroeuropea mostró más forámenes unilaterales (29,5 %), mientras que la muestra africana mostró más forámenes bilaterales (40,8 %). El diámetro del foramen parietal promedió 1,98 mm y 1,88 mm para las muestras europeas y africanas, respectivamente. En este estudio, se observó un foramen medio en la sutura sagital en 14 de los cráneos en general (4 %). El estudio demostró que los forámenes parietales son más frecuentes de lo previsto en ambos grupos de población. Los hallazgos de este estudio, que indican una mayor prevalencia y la subsiguiente posibilidad de que se encuentren más venas emisarias, pueden ser útiles para mejorar la comprensión de las variaciones en la prevalencia y las implicaciones clínicas del foramen parietal entre varios grupos de población ubicados en el mundo.

ANATOMICAL VARIATIONS OF THE PARIETAL FORAMEN AND ITS RELATIONS TO THE CALVARIAL LANDMARKS: A CROSS-SECTIONAL CADAVERIC STUDY.

OBJECTIVE: The aim: Estimate the prevalence of the parietal foramen in the adult human skulls of Ukrainian origin, and study its morphology and relationships to main anatomical landmarks of the skull. PATIENTS AND METHODS: Materials and methods: A cross-sectional observational study of PF was conducted with 42 random cadaveric adult human skull roofs (calvaria) collected from the laboratory and museum of Human Anatomy Department, Kharkiv National Medical University, Ukraine. The patency and the length of the PF canal were determined, and PF external/internal diameters and the distance to the calvarial landmarks from PF were measured using the caliper. Mean and standard deviation were calculated to compare with the existing data. RESULTS: Results: In the present study 85.7% (n = 36) of the calvaria had the PF, 54.8% (n = 23) had bilateral location of PF, 30.9% (n = 13) had unilateral presence of PF (right side: 23.8%, n=10 and left side: 7.1%, n=3), and 14.3 % (n = 6) demonstrated bilateral absence of PF. CONCLUSION: Conclusions: An anatomical variation in parietal foramen is not uncommon, and the differences can be based on multiple factors like geography and race. It is important to have detailed information on anatomical variations in different population groups to facilitate surgical and radiological interventions.

Anatomical observation and significance of the parietal foramen in Chinese adults.

BACKGROUND: This study aimed to investigate the incidence, number, diameter, and relative location of the parietal foramen (PF) as well as communication of intracranial and extracranial orifices and their direction, and sagittal suture morphology and length. MATERIALS AND METHODS: A total of 280 dry Chinese adult skull specimens from the Department of Anatomy, Southern Medical University, were observed and measured. The occurrence rate and quantity of the PF near the sagittal suture were recorded. The aperture of the PF, the vertical distance between PF and sagittal suture, and the linear distance between PF and lambda were measured using a Vernier calliper. The length of the sagittal suture was measured by a flexible ruler; the direction and communication of intracranial and extracranial orifices were detected using a probe. RESULTS: The total incidence of the PF was 82.86%, slightly higher on the right side than on the left side. The single-foramen type was the most prevalent. The mean diameter of the PF on the left and right sides were 1.02 ± 0.72 mm and 1.07 ± 0.67 mm, respectively, and the diameter of the PF on the sagittal suture was 1.77 ± 0.44 mm. The mean vertical distance between the PF and the sagittal suture was 5.90 ± 2.78 mm and 5.85 ± 2.75 mm on the left and right sides, respectively. The shape of the sagittal suture in the PF area was primarily dentate shaped, with an average arc length of χ = 124.36 ± 7.76 mm, of which the majority were completely healed type. The intracranial and extracranial communication was 39.97%, and the majority of the PF were anteromedial direction. CONCLUSIONS: The current study provided an anatomical basis for imaging diagnosis and neurosurgery by investigating the incidence, diameter, and relative location of the PF and intracranial and extracranial communication and direction.

The parietal foramen anatomy: studies using dry skulls, cadaver and in vivo MRI.

OBJECTIVE: The aim of this study was to describe the anatomical features encountered in the parietal foramen in a series of 178 human bones and 123 head MRI examinations. A cadaveric specimen was also dissected to demonstrate the trajectory of a superficial scalp vein through the parietal foramen as far as the dura mater. A literature review was performed regarding prevalence of parietal foramen in different populations. METHODS: Totally, 178 paired adult bones were used to investigate the presence, shape and number of the parietal foramina. In addition, 123 brain MRI examinations were also studied. RESULTS: The parietal foramina were encountered in 75/89 (84.3%) skulls [32/38 (84.2%) in women vs. 43/51 (84.3%) in men, p > 0.05]. The parietal foramen was present bilaterally in 44.73% of females and 54.9% of males. Regarding unilaterality of the parietal foramen, a right or left laterality was observed in female 21% right versus 18% left; and 16% versus 14% (left) in males (p > 0.05). The accessory parietal foramen was present in the right parietal in 2.6% and in 7.9% on the left side of the females, while 5.9% and 3.9% of the males on the right or left sides, respectively. The parietal foramina located in the proximity of the sagittal suture (male 7.1 ± 2.5 mm vs. female, 7.4 ± 2.7 mm). There was a positive correlation between the right and left parietal foramina regarding the distance from the median line. The distance from a foramen to the contralateral one was 16 ± 4 mm in men and 18 ± 5 mm in women, respectively (p > 0.05). CONCLUSION: No major differences were encountered between sexes regarding the anatomical features of parietal foramen.

Parietal foramen: incidence and topography.

BACKGROUND: The parietal foramen (PF) is a small inconsistent aperture located at the border of the middle 1/3 and posterior 1/3 of the parietal bone near the sagittal suture and is considered an emissary foramen. Cranial emissary foramina are of utmost importance due to the structures that traverse the foramen. Variations in these foramina are common. Knowledge of the PF is important when performing neurosurgical procedures as the emissary vessels are at risk. MATERIALS AND METHODS: The present study used 100 dry adult calvaria to determine the frequency of PF, the diameter of the PF, as well as topography of the PF (using the sagittal suture as an anatomical landmark). RESULTS: A total of 32% of calvaria had PF present bilaterally; whilst 35% of calvaria had unilateral PF. The study also reports 5% calvaria in which PF were present on the sagittal suture. The mean diameter recorded was 1.55 mm (0.74-3.08 mm), and the mean distance between the lateral margin of the PF and the sagittal suture was 9.02 mm (4.44-18.20 mm). CONCLUSIONS: Knowledge of the incidence and topography of the PF may aid neurosurgeons in creating and adjusting techniques and procedures in order to mitigate the risk of injury to emissary veins and other structures emerging from the PF.

Novel vascular plexus in the head of a sea snake (Elapidae, Hydrophiinae) revealed by high-resolution computed tomography and histology.

Novel phenotypes are often linked to major ecological transitions during evolution. Here, we describe for the first time an unusual network of large blood vessels in the head of the sea snake Hydrophis cyanocinctus. MicroCT imaging and histology reveal an intricate modified cephalic vascular network (MCVN) that underlies a broad area of skin between the snout and the roof of the head. It is mostly composed of large veins and sinuses and converges posterodorsally into a large vein (sometimes paired) that penetrates the skull through the parietal bone. Endocranially, this blood vessel leads into the dorsal cerebral sinus, and from there, a pair of large veins depart ventrally to enter the brain. We compare the condition observed in H. cyanocinctus with that of other elapids and discuss the possible functions of this unusual vascular network. Sea snakes have low oxygen partial pressure in their arterial blood that facilitates cutaneous respiration, potentially limiting the availability of oxygen to the brain. We conclude that this novel vascular structure draining directly to the brain is a further elaboration of the sea snakes' cutaneous respiratory anatomy, the most likely function of which is to provide the brain with an additional supply of oxygen.

Subcutaneous Extension of Parasagittal Atypical Meningioma Through Parietal Foramen.

Meningiomas extended to the scalp without any bony changes are rare. A 79-year-old man presented with a large subcutaneous mass in the midline parieto-occipital region and progressive right hemiparesis. The contrast-enhanced millimetric computed tomography scans of the head showed the intracranial parasagittal enhanced mass invading the superior sagittal sinus and the subcutaneous mass without any bony destructive, osteoblastic, or osteolytic changes. Under the operative microscope, no visible communication was found between the intracranial and extracranial mass lesions. Histopathologic examination of both intracranial and extracranial tumors demonstrated the same atypical meningioma (World Health Organization grade II). The possible route of extracranial extension of the tumor may be the sizable parietal foramen.

Trepanation and enlarged parietal foramen on skulls from the Loyalty Islands (Melanesia).

The goal of this study is a comprehensive examination of openings discovered on two skulls in the collection of skeletal remains from the Loyalty Islands (Melanesia). The skull No. 1524 displayed an evidence of successful trepanation, and the skull No. 7985 revealed openings that were reminiscent of a trepanation, however, we are inclined to believe that in the latter case we are dealing with a rare genetic anomaly - enlarged parietal foramen.

The extracranial to intracranial anastomotic channel through the parietal foramen: delineation with magnetic resonance imaging.

PURPOSE: Parietal foramina (PFs) are openings of fine canals that perforate the parietal bone. However, few studies have investigated the entire canals and their emissary vessels (EVs). Here, we explore the EVs with magnetic resonance imaging. METHODS: A total of 104 patients who underwent contrast examinations and exhibited an intact scalp, skull, dura mater, and superior sagittal sinus were enrolled in this study. Imaging data were obtained as thin-sliced, seamless sagittal sections and were transferred to a workstation for analysis. RESULTS: A total of 116 EVs passing through the PF and inner canals (parietal canal) were identified in 78 patients (75 %). All the EVs were found to perforate each layer of the parietal bone. Of 104 patients, 68 % exhibited one EV, 30 % two EVs, and 2 % three EVs. In 85.3 %, the EV was entirely delineated in one sagittal slice, 10.3 % were covered by two slices, and 4.3 % by three slices. In 68 %, the EV connected to the upper surface of the superior sagittal sinus (SSS) with variable courses from near-vertical to horizontal inclinations. CONCLUSIONS: EVs perforate the skull with variable inclinations, while showing a highly consistent course in the sagittal dimension. The PF and EV can be used as landmarks of the SSS lying immediately below.

Enlarged parietal foramina: a rare forensic autopsy finding.

Enlarged parietal foramina (EPF) are a quite rare developmental defect of the parietal bone which has to be distinguished from the normal small parietal foramina. We report a forensic case of an individual found in an advanced state of putrefaction in his own house with an undetermined cause of death. No evidence of trauma was observed, and the toxicological exam was negative. The victim was a 40-year-old man with a history of epilepsy. The large biparietal foramina, a rare anatomical variation and unusual autopsy finding, were observed at autopsy. The recognition of anatomical variations is important to avoid false interpretations and conclusions and has a significant potential as an identity factor, thus contributing to positive identification.

Physiological implications of the abnormal absence of the parietal foramen in a late Permian cynodont (Therapsida).

The third eye (pineal eye), an organ responsible for regulating exposure to sunlight in extant ectotherms, is located in an opening on the dorsal surface of the skull, the parietal foramen. The parietal foramen is absent in extant mammals but often observed in basal therapsids, the stem-group to true mammals. Here, we report the absence of the parietal foramen in a specimen of Cynosaurus suppostus, a Late Permian cynodont from South Africa (SA). Comparison with Procynosuchus delaharpeae, a contemporaneous non-mammalian cynodont from SA, demonstrates that the absence of this foramen is an abnormal condition for such a basal species. Because seasonality was marked during the Late Permian in SA, it is proposed that the third eye was functionally redundant in Cynosaurus, possibly due to the acquisition of better thermoregulation or the evolution of specialized cells in the lateral eyes to compensate for the role of the third eye.

Relationship of the parietal foramen and complexity of the human sagittal suture / Relación del foramen parietal y la complejidad de la sutura sagital humana

The purpose of this paper is to report on the relationship between the parietal foramen and complexity of the human sagittal suture. Examination of 110 Japanese human skulls (males=67, females=43) with at least one parietal foramen revealed that the sagittal suture in the area of the Obelion was the simplest portion (i.e., fewest interdigitations and shortest length) of the suture (paired t-test, P<0.0005), when compared to the outstretched suture length of three established sections: 1. Parietal foramen section (P); 2. Anterior to section P (B); and 3. Posterior to section P (L). Sutural complexity was also compared between individuals with unilateral foramen (n=48) and bilateral foramina (n=62) to see if there was a statistically significant difference. The results revealed a slight difference in section P (ANOVA Bonferroni, P<0.05), denoting that the sagittal suture at the Obelion in individuals with unilateral parietal foramen is more complex than in individuals with bilateral foramina. While no difference in sex was noted, this simplicity in part likely reflects redirected bone stresses around a circular opening resulting in reduced tensile stresses and increased compressive stresses adjacent to the parietal foramen. This phenomenon warrants additional research and has implications for bone biomechanics and development of the cranial sutures.

El propósito de este trabajo es informar sobre la relación entre el foramen parietal y la complejidad de la sutura sagital en humanos. Se examinaron 110 cráneos humanos de individuos japoneses (hombres = 67, mujeres = 43) con al menos un foramen parietal, revelando que la sutura sagital en el área del obelion fue la parte más simple (es decir, menos interdigitaciones y menor longitud) de la sutura (vinculado la prueba t, p <0,0005). Cuando se comparó la extensión de la longitud de la sutura se establecieron tres secciones: 1. Sección foramen parietal (P); 2. Anterior a la sección P (B), y 3. Posterior a la sección P (L). La complejidad de la sutura también fue comparada entre los individuos con foramen unilateral (n = 48) y forámenes bilaterales (n = 62) para ver si había una diferencia estadísticamente significativa. Los resultados revelaron una ligera diferencia en la sección P (ANOVA Bonferroni, P <0,05), que indica que la sutura sagital a nivel del obelion en los individuos con foramen parietal unilateral es más compleja que en los individuos con forámenes bilaterales. Si bien no hubo diferencia según sexo, esta simplicidad en parte, probablemente refleja la redirección de las fuerzas del hueso alrededor de una abertura circular, lo que reduce la resistencia a la tracción y aumenta la fuerza de compresión adyacente al foramen parietal. Este fenómeno justifica la investigación adicional y tiene implicaciones para el desarrollo óseo y biomecánica de las suturas craneales.