Pontine Flexure Research Articles

Ultrasound visualization of the central nervous system during embryonic and fetal periods: Neurosonoembryology utilizing multiple three-dimensional transvaginal ultrasound technology.

To study the ultrasonographic features of the central nervous system (CNS) in normally developing embryos and fetuses with a crown-rump length (CRL) of 10-84mm, utilizing a high-frequency transvaginal probe in conjunction with various three-dimensional (3D) imaging modes. From January 2020 to February 2021, 210 normally developing embryos and fetuses in early pregnancy were enrolled and classified based on their gestational age. A high-frequency transvaginal transducer was used to perform 2D and 3D ultrasounds, and the 3D images were saved. These images were then processed using multiple 3D technologies, such as HD live silhouette, OmniView, and TUI. Additionally, the circumference of the vermis was measured through the posterior fontanelle. Beginning at the 10mm CRL stage of embryonic development, high-frequency transvaginal 3D ultrasound imaging was able to clearly visualize the prosencephalon, mesencephalon, and rhombencephalon. Notable changes were observed in the rhombencephalon during the 16-22mm CRL stage, including the visualization of the pontine flexure and cerebellar primordium. At 23-40mm CRL, there was a distinct pontine flexure, and the developing cerebellum, the fourth ventricle, and choroid plexus of the fourth ventricle (4th VCP) could be observed. The roof of the rhombencephalon was partitioned by the 4th VCP into the anterior membranous area (AMA) located rostrally and the posterior membranous area situated caudally. Additionally, the original Blake's pouch was identifiable. Among fetuses measuring 41-84mm CRL, the AMA progressively decreased in size as the vermis developed. From the mid-sagittal view, the orientation of the 4th VCP seemed to shift from being perpendicular to the neural tube's long axis to being parallel to it. Furthermore, there was a significant correlation between CRL and vermis circumference. Using three-dimensional transvaginal ultrasound scanning, detailed visualization of the morphological changes in the CNS during normal embryonic development from 7 to 13+6 weeks is possible. This technology can aid in accurately characterizing the embryonic origin of the CNS.

Endocasts of the basal sauropsid Captorhinus reveal unexpected neurological diversity in early reptiles.

Captorhinids are a group of Paleozoic amniotes that represents one of the earliest-diverging clades of eureptiles. Although captorhinids are one of the best-known and most well-studied clades of early amniotes, their palaeoneuroanatomy has gone largely unexamined. We utilized neutron computed tomography to study the virtual cranial and otic endocasts of two captorhinid specimens. The neurosensory anatomy of captorhinids shows a mixture of traits considered plesiomorphic for sauropsids (no expansions of the cerebrum or olfactory bulbs, low degree of encephalization, low ossification of the otic capsule) and those considered more derived, including moderate cephalic and pontine flexures and a dorsoventrally tall bony labyrinth. The inner ear clearly preserves the elliptical, sub-orthogonal canals and the short, rounded vestibule, along with an unusually enlarged lateral canal and a unique curvature of the posterior canal. The reconstructed neurosensory anatomy indicates that captorhinids were sensitive to slightly higher frequencies than many of their contemporaries, likely reflecting differences in body size across taxa, while the morphology of the maxillary canal suggests a simple, tubular condition as the plesiomorphic state for Sauropsida and contributes to the ongoing discussions regarding the phylogenetic placement of varanopids. This study represents the first detailed tomographic study of the brain and inner ear of any basal eureptile. The new data described here reveal that the neuroanatomy of early sauropsids is far more complex and diverse than previously anticipated, and provide impetus for further exploration of the palaeoneuroanatomy of early amniotes.

Familial chiari malformation

Chiari malformation type 1 (CM 1) is defined as herniation of cerebellar tonsils 4-5 mm below the foramen magnum. Multiple developmental factors like defective development of pontine flexure and shallow posterior fossa are the proposed factors which predispose the development of this syndrome. These reports on familial occurrence of this syndrome correlates with the embryonal- developmental etiology of Chiari 1 malformation. Recent advances in the understanding of the influence of genes and pathogenesis of familial Chiari malformation are expected to improve management of affected patients and monitoring of at-risk family members.

Neural and endocranial anatomy of Triassic phytosaurian reptiles and convergence with fossil and modern crocodylians.

Phytosaurs are a clade of large, carnivorous pseudosuchian archosaurs from the Late Triassic with a near cosmopolitan distribution. Their superficial resemblance to longirostrine (long-snouted) crocodylians, such as gharials, has often been used in the past to infer ecological and behavioural convergence between the two groups. Although more than thirty species of phytosaur are currently recognised, little is known about the endocranial anatomy of this clade. Here, we describe the endocranial anatomy (including the brain, inner ear, neurovascular structures and sinus systems) of the two non-mystriosuchine phytosaurs Parasuchus angustifrons (=“Paleorhinus angustifrons”) and Ebrachosuchus neukami from the Late Triassic of Germany based on digital reconstructions. Results show that the endocasts of both taxa are very similar to each other in their rostrocaudally elongate morphology, with long olfactory tracts, weakly demarcated cerebral regions and dorsoventrally short endosseous labyrinths. In addition, several sinuses, including large antorbital sinuses and prominent dural venous sinuses, were reconstructed. Comparisons with the endocranial anatomy of derived phytosaurs indicate that Phytosauria is united by the presence of elongate olfactory tracts and longitudinally arranged brain architecture—characters which are also shared with Crocodyliformes. However, a substantial morphological variability is observed in the cephalic and pontine flexure and the presence of a pineal organ across the different phytosaur species. These results suggest that the endocranial anatomy in Phytosauria generally follows a plesiomorphic pattern, with moderate variation within the clade likely resulting from divergent sensory and behavioural adaptations.

Morphogenesis of the inner ear at different stages of normal human development.

This study examined the external morphology and morphometry of the human embryonic inner ear membranous labyrinth and documented its three-dimensional position in the developing embryo using phase-contrast X-ray computed tomography and magnetic resonance imaging. A total of 27 samples between Carnegie stage (CS) 17 and the postembryonic phase during trimester 1 (approximately 6-10 weeks after fertilization) were included. The otic vesicle elongated along the dorso-ventral axis and differentiated into the end lymphatic appendage and cochlear duct (CD) at CS 17. The spiral course of the CD began at CS18, with anterior and posterior semicircular ducts (SDs) forming prominent circles with a common crus. The spiral course of the CD comprised more than two turns at the postembryonic phase, at which time the height of the CD was evident. A linear increase was observed in the length of anterior, posterior, and lateral SDs, in that order, and the length of the CD increased exponentially over the course of development. Bending in the medial direction was observed between the cochlear and vestibular parts from the latero-caudal view, with the angle decreasing during development. The position of the inner ear was stable throughout the period of observation on the lateral to ventral side of the rhombencephalon, caudal to the pontine flexure, and adjacent to the auditory ganglia. The plane of the lateral semicircular canal was approximately 8.0°-14.6° with respect to the cranial caudal (z-)axis, indicating that the orientation of the inner ear changes during growth to adulthood.

Braincase Anatomy of the Basal TheropodSinosaurusfrom the Early Jurassic of China

The neuroanatomy of the mid-sized theropod Sinosaurus triassicus from the Lower Jurassic Lufeng Formation, Lufeng Basin in Yunnan Province, China was studied using X-ray computed tomography. The braincase is characterized by a large supraoccipital knob that is capped by a posterior projection of the parietal and two external foramina for the caudal middle cerebral vein, which is completely enclosed by the supraoccipital. The basicranium has well defined, short basipterygoid processes that project ventral to the basal tubera. The basisphenoid is expanded, projects posteroventrally, and is pierced by four pneumatic recesses. The endocranial morphology resembles that observed in other basal theropods—in particular some allosauroids—and has a strongly marked pontine flexure and a large dorsal expansion. The inner ear morphology is also similar to that observed in other basal theropods, with slender semicircular canals. The anterior semicircular canal is 20% larger than the posterior semicircular canal, and the angle formed between them is less than 90° when seen in dorsal view.

Inferior vermian hypoplasia – preconception, misconception

Inferior vermian hypoplasia – preconception, misconception

Neuroanatomy of the Marine Jurassic Turtle Plesiochelys etalloni (Testudinata, Plesiochelyidae)

Turtles are one of the least explored clades regarding endocranial anatomy with few available descriptions of the brain and inner ear of extant representatives. In addition, the paleoneurology of extinct turtles is poorly known and based on only a few natural cranial endocasts. The main goal of this study is to provide for the first time a detailed description of the neuroanatomy of an extinct turtle, the Late Jurassic Plesiochelysetalloni , including internal carotid circulation, cranial endocast and inner ear, based on the first digital 3D reconstruction using micro CT scans. The general shape of the cranial endocast of P. etalloni is tubular, with poorly marked cephalic and pontine flexures. Anteriorly, the olfactory bulbs are clearly differentiated suggesting larger bulbs than in any other described extinct or extant turtle, and indicating a higher capacity of olfaction in this taxon. The morphology of the inner ear of P . etalloni is comparable to that of extant turtles and resembles those of slow-moving terrestrial vertebrates, with markedly low, short and robust semicircular canals, and a reduced lagena. In P . etalloni the arterial pattern is similar to that found in extant cryptodires, where all the internal carotid branches are protected by bone. As the knowledge of paleoneurology in turtles is scarce and the application of modern techniques such as 3D reconstructions based on CT scans is almost unexplored in this clade, we hope this paper will trigger similar investigations of this type in other turtle taxa.

Ontogenetic trajectories in the ornithischian endocranium

Understanding ontogenetic and developmental patterns is critical for reconstructing the life history of fossil vertebrates. In dinosaurs, ontogenetic studies have nearly exclusively focused on changes in the cranial and post-cranial skeleton, whereas ontogenetic changes in the endocranium have received little attention. Here, we present digital reconstructions of the brain and inner ear anatomy of two ontogenetic stages of the Jurassic ornithischian dinosaur Dysalotosaurus lettowvorbecki. Results show that the endocranial anatomy underwent considerable changes during growth, including a rostrocaudal elongation of the olfactory apparatus, a reduction in the cephalic and pontine flexure and an increase in cerebellum size. Functional elements, such as the cerebral hemispheres and the inner ear, were already well developed in early ontogenetic stages, indicating a large degree of precociality. The anisotropic pattern of size and shape changes in the endocranium further indicates that ontogenetic trajectories may be controlled by functional and environmental demands in the different growth stages in Dysalotosaurus lettowvorbecki. The occurrence of similar ontogenetic patterns in the endocranial anatomy of derived ornithopod dinosaurs suggests a more widespread distribution of this growth trajectory.

Cranial endocast of the carcharodontosaurid theropod Giganotosaurus carolinii Coria Salgado, 1995

A complete endocast of Giganotosaurus carolinii CORIA & SALGADO, 1995 was made in latex after removing mechanically the sediment filling of the cerebral cavity of the braincase, thereby allowing the description of the endocranial anatomy of the specimen. The endocast was compared with the other few known natural or artificial theropod endocasts, including the two species of the African allosauroid species Carcharodontosaurus saharicus and C. idiguensis. As in Carcharodontosaurus, the olfactory bulbs in Giganotosaurus are aligned with the forebrain, the midbrain is posteroventrally inclined and the hindbrain is parallel but ventral to the forebrain, showing similarly angled cephalic and pontine flexures. The cranial nerves and blood vessels have a similar disposition as in Carcharodontosaurus saharicus. However, in Giganotosaurus there is only one branch for cranial nerve XII, and cranial nerve XI has a separate internal opening from the vagus foramen (metotic foramen). In C. saharicus, there is a separate opening as well, but it is anterior in position and was probably utilized by cranial nerve IX. The length of the endocast of Giganotosaurus, including the olfactory bulbs, is approximately 19 % longer than the endocast in Carcharodontosaurus saharicus.

The Braincase of Apatosaurus (Dinosauria: Sauropoda) Based on Computed Tomography of a New Specimen with Comments on Variation and Evolution in Sauropod Neuroanatomy

We describe a previously unreported braincase of the sauropod dinosaur Apatosaurus from the Cactus Park Quarry, Morrison Formation of western Colorado using high-resolution X-ray computed tomography. The digital nature of these data allowed us to prepare and describe the first three-dimensional rendering of the endocranial space in this historically important dinosaur species. Results are compared with a range of taxa drawn from across the sauropod tree revealing previously underappreciated variation in the sauropod neurocranium. Examples of variable characters include the degree of cerebral and pontine flexure, the morphology of the parietal body and superior sagittal sinus and their relationship with the overlying dermal roof, and the conformation of several cranial nerve foramina. We provide preliminary evolutionary hypotheses and discussion for many of these features. The recognition that considerable variation is present in the sauropod neurocranium hopefully will encourage more detailed descriptions of this anatomically complex region, as well as facilitating a synthetic review of the sauropodomorph braincase as these descriptions become available.

Embriologia e genetica dello sviluppo cerebellare

During the fourth week of development, the mesencephalic flexure and cervical flexure appear in the cranial region of the neural tube, delimiting three neural vescicles: the prosencephalon, mesencephalon and rhomboencephalon. During the fifth week, the pontine flexure forms in the roof of the rhomboencephalon, marking the division between the metencephalon and myeloencephalon, the future medulla oblongata. The dorsal part of the metencephalon (alar plate), between the mesencaphalic isthmus and the pontine flexure, will give rise to the cerebellum, whereas its ventral part (basal plate) will give rise to the pons. The alar plates, lateral to the deepening pontine fissure and the hindbrain cavity, present an intense proliferative activity with the formation of two extensions which fuse just behind the isthmus to form the cerebellar plate. During the sixth week of development, the rhombic lips appear in the posterolateral regions of this strip and after persistent proliferative activity they fuse along the median line. Median thickening of this region will give rise to the vermis, while the two lateral masses become the lateral lobes. During the seventh week, the flocculonodular lobe will form. Between the eighth and ninth weeks, the vermis expands caudally with progressive dilatation of the fourth ventricle whose Luschka and Magendie foramina are still unperforated. The cerebellar proliferation and differentiation processes are correlated to the activity of two separate germinal areas: the ependymal ventricle and the rhombic lip. From the eighth week, neuroblastic migration starts from the rhombic lip which in successive genetically controlled steps leads to the formation of the external granular layer of the cerebellar cortex. From the ventriculo-ependymal zone cells migrate to form the cerebellar nuclei destined to differentiate into Purkinje cells. The cerebellar recess starts to develop around the twelfth week with the formation of the primary fissure separating the anterior and posterior parts of the cerebellum to end with the complete formation of all cerebellar lobes at around the twenty-fourth week of development. The foliation process starts when the recess has formed and continues in the first months of life after birth. The processes of cell development and differentiation are genetically programmed and the outcome of an interaction between genetic and environmental factors. The different stages of embryonic development are thought to be controlled by sequential ordered activation of genetic clusters (homeotypic genes) which in turn encode for a series of molecules directly involved in the regulation of cell and tissue interactions. There is increasing evidence of genetic involvement in the different types of cerebellar malformation whose expression and association with other extracerebellar malformations depends on the developmental age at which the genetic change occurred.

Changes in the CSF fluid pathways in the developing rat fetus with early onset hydrocephalus.

Interest in the factors involved in the abnormal cortical development of the HTx rat fetus have led us to re-examine the structural and morphological changes in the CSF pathways preceding constriction and blockage of the cerebral aqueduct. Histological analysis was carried out on coronal and sagittal sections from HTx and Wistar fetuses. The aqueduct is found to be a broad channel extending from the posterior end of the third ventricle that ends in a blind pouch above the developing cerebellum. The aqueduct drains into the fourth ventricle via a vertically orientated, narrow channel lying between the posterior aspect of the pontine flexure and the anterior surface of the cerebellum. On Day E18 the connecting channel between the aqueduct and the fourth ventricle is blocked by apposition of its walls. 24 hours later the lateral ventricles begin to dilate and the anterior end of the aqueduct is blocked and the connecting channel between the aqueduct and the fourth ventricle reopens. The cause of these sequential changes in the CSF fluid pathways remains speculative.

Immunocytochemical detection of Reissner's fiber-like glycoproteins in the subcommissural organ and the floor plate of wildtype and cyclops mutant zebrafish larvae.

The subcommissural organ (SCO) and the floor plate (FP) secrete high molecular weight glycoproteins that polymerize in the form of the Reissner's fiber (RF). To study to what extent the absence of the FP affects the expression of these glycoproteins, we have investigated the brain and spinal cord of 48-h and 72-h wildtype and cyclops (cyc) mutant zebrafish larvae by using a polyclonal antiserum against bovine RF. Wildtype larvae showed immunoreactivity in the SCO at the dorsal forebrain-midbrain boundary. In the ventricle, over the SCO surface, thin immunoreactive fibers aggregated into an RF that ran along the third and fourth ventricles and the central canal of the spinal cord until, at its caudal end, the fiber disintegrated and formed a strongly immunoreactive massa caudalis that left the neural tube and invaded the surrounding tissues of the tail fin. The rostral end of the FP, lining the pontine flexure, was also strongly immunoreactive, as was the caudal third of the FP. Cyc mutants showed an immunoreactive SCO and fibrous material in the ventricle, but an RF was missing. There was no label in the ventral midline of the neural tube except in some specimens in which the caudal FP persisted and was immunoreactive. It is concluded that the product of the cyc gene is not required for the expression of SCO glycoproteins but for their polymerization into an RF in the brain ventricles.

Rostral floor plate (flexural organ) secretes glycoproteins immunologically similar to subcommissural organ glycoproteins in dogfish ( Scyliorhinus canicula) embryos

The subcommissural organ of vertebrates secretes glycoproteins into the cerebrospinal fluid of the third cerebral ventricle. This material polymerizes in Reissner's fiber. During ontogenetic development, besides the subcommissural organ, the ependyma lining the pontine flexure constitutes an additional Reissner's fiber-secreting gland named flexural organ. We have studied the secretion of the flexural organ and the subcommissural organ in dogfish ( Scyliorhinus canicula) embryos using three different antisera and the lectins concanavalin A and wheat germ agglutinin. AFRU is an antiserum against the bovine Reissner's fiber; Ab-600 is an antiserum against 600 kDa dogfish subcommissural organ glycoproteins; and APSO is an antiserum against immunoaffinity purified bovine subcommissural organ secretory glycoproteins. These three antisera immunostained the flexural organ indicating that it contains epitopes similar to those present in bovine and dogfish subcommissural organ glycoproteins. It seems highly probable that the flexural organ and the subcommissural organ of dogfish embryos secrete similar compound(s). Other ependymal regions were also immunostained with Ab-600 and APSO antisera. Then, Reissner's fiber-like glycoproteins were transiently expressed by most embryonary ependymal cells. These glycoproteins might play a role in the development of the central nervous system of vertebrates.

Morphological characteristics of the developing human brain during the embryonic period.

Many features of the developing nervous system are visible from external observations of intact human embryos. In this study, a photographic atlas from the 4th to the 7th week after ovulation (Carnegie stages 10-18) is provided. The neural folds began to fuse at stage 10, and the rostral and caudal neuropore were closed during stages 11 and 12, respectively. The three primary divisions of the brain were distinguishable before closing of the neural tube. The five secondary brain vesicles were formed during stages 14-15. The development of the cerebellum and cerebrum were first observed at stages 14 and 15, respectively. The mesencephalic flexure was seen at stage 12, and the cervical flexure and pontine flexure at stage 14. After stages 18-19, it became increasingly difficult to identify detailed features of the brain from the surface. Results from this study will help to correlate the characteristic findings of the developing central nervous system of human embryos from stereomicroscopical and light microscopical observations and to locate the exact parts of the developing human brain for other purposes.

Endocranial casts of early archosaurian reptiles

The first endocranial casts from non-crown-group archosaurian reptiles are described. Synthetic casts were made of the preserved parts of the endocranial cavities ofErythrosuchus africanus,Vjushkovia triplicostata andXilousuchus sapingensis. These casts are incomplete, but they reveal a substantial amount of information on the form of the early archosaur brain and inner ear. Cranial and pontine flexures are equal in bothErythrosuchus (45°) andV. triplicostata (35–40°). The endocasts ofXilousuchus andV. triplicostata are characterised by the possession of a pseudolagena and a quantifiable down-slope from the myelencephalon to the metencephalon — features that have yet to be described for other reptilian endocranial casts.

Localization and ontogeny of the orphan receptor OR-1 in the rat brain.

This study describes the expression of the OR-1 orphan receptor in embryonic, postnatal, and adult brain tissue studied by in situ hybridization. This newly characterized member of the nuclear receptor superfamily functions as a modulator of retinoic acid and thyroid hormone signalling by influencing gene activation by these hormones from a distinct promoter region. In the fetal brain OR-1 mRNA was observed from E13-E16 in the developing pons, tegmentum, pontine flexure, medulla, inferior and superior colliculi, cerebellum, hippocampus, thalamus, striatum, and cortical plate. At E18, OR-1 was expressed in the hippocampus, cerebellum, ventricular layer of the developing cortex and cortical plate, striatum, and olfactory bulb. In the E21 to early postnatal brain the highest expression of OR-1 mRNA was seen in the hippocampus, cerebellum, striatum, and olfactory bulb. The expression of OR-1 in the cerebellum increased during postnatal development and by d P21 OR-1 mRNA had reached the levels present in the adult in the cerebellar cortex. In the adult brain the highest expression of OR-1 mRNA was observed in the CA1 area of the hippocampus and the cerebellar cortex. We conclude that OR-1 is widely expressed in the fetal brain, whereas in the postnatal and adult brains OR-1 mRNA is more discretely localized, and that the amount of OR-1 mRNA increases in the cerebellum during postnatal development. The results of this study suggest that, in the fetal brain, OR-1 has a spatially widespread role in modulating gene activation by retinoids and thyroid hormone, whereas in the adult brain this modulation occurs only in distinct neuronal populations.

Ontogenesis of prolactin receptor gene expression in the rat olfactory system: potential roles for lactogenic hormones in olfactory development.

The PRL receptor (PRLR) is expressed at very low levels in the olfactory bulb of the adult rat but is detected in abundance in the olfactory epithelium and olfactory bulb of the fetal rat in late gestation. To explore potential roles for the lactogenic hormones in olfactory differentiation and development, we have used in situ hybridization and immunohistochemistry to examine the ontogeny of PRLR gene expression in the rat olfactory system. At midgestation (embryonic day 12.5), messenger RNAs (mRNAs) encoding the long and short isoforms of the rat PRLR were detected in the medial and lateral nasal processes, the epithelial lining of the olfactory pit, and the neuroepithelium lining the cerebral ventricles in the region of the rhinencephalon. PRLR mRNA was also expressed prominently in the frontonasal mesenchyme and in mesenchymal tissue underlying the developing brain and overlying the pontine flexure in the interpeduncular fossa. The distribution of PRLR immunoreactivity was similar to that of PRLR mRNA, indicating that the PRLR gene is translated to that of PRLR mRNA, indicating that the PRLR gene is translated to lactogenic binding protein in the rat embryo in vivo. With advancing gestation, the PRLR was expressed intensely, although discontinuously, in the olfactory epithelium and was detected in the cartilage primordia of the ethmoid, sphenoid, temporal, and mandibular bones. PRLR expression in the vomeronasal organ was confined to the luminal epithelial surface. PRLR mRNA and immunoreactive protein were first detected in the olfactory bulb on embryonic day 18. PRLR expression was most intense initially in the periventricular neuroepithelium; subsequently, robust staining of the mitral and tufted cell neurons became apparent, accompanied by intense PRLR expression in the sensory neuronal cell bodies of the olfactory epithelium. By postnatal day 5, the PRLR was expressed in abundance in mitral and tufted cells of the olfactory bulb and in neuronal cell bodies of the anterior olfactory nucleus and the piriform cortex. PRLR mRNA was also detected in the mitral cells of the olfactory bulb of the lactating rat, although at levels far lower than those in the fetal or neonatal rat. The expression of the PRLR in the olfactory system of the fetal and neonatal rat implicates novel roles for the lactogenic hormones in olfactory differentiation and development and may provide new mechanisms by which the lactogens may regulate neonatal behavior and maternal-infant interactions.

Mode of neuronal migration of the pontine stream in fetal mice

The migration of immature neurons in the pontomedullary subpial region was examined in fetal mice by light and electron microscopy. Immature pontine cells were observed forming a cell strand from the ventral aspect of the fourth ventricle to the pontine flexure during the period between the 14th and 17th day of gestation. These cells were elongated and oriented parallel to the direction of migration, and displayed features of immature neurons: they contained a high concentration of ribosomal rosettes and a few cisternae of rough endoplasmic reticula, as well as Golgi apparatus, mitochondria, microtubules and centrioles. Many of the neurons extended leading processes, and these contained longitudinally-arrayed microtubules. Filopodia extending from the processes were found beneath the pia mater. Relocating cells displayed contact relationships between themselves; in the caudal part of the stream, translocating neurons were apposed to each other and fibers of various diameters, and in the rostral area of the stream, many fibers were noted, and corresponded to leading processes of relocating neurons, to which other cell bodies had close contact. From the arrangement of the immature neurons and their processes, it can be inferred that developing fibers act as guidance substrates for the translocation of embryonic pontine neurons.