Ontogeny of the partial secondary wall of the otoccipital region of the endocranium in prehatching Alligator mississippiensis (Archosauria, Crocodylia)

The ontogeny of the posterior otic and anterior occipital portions of the neural endocranium of prehatching Alligator mississippiensis was investigated by reconstruction from sectioned material. In Stage 6 of this species, in which the endochondral ossification of the otoccipital region of the neural endocranium is only in its very early stage, two bony outgrowths-laminae-are present at the external wall of the posterior portion of the neural endocranium. The anterior lamina arises from the external surface of the basal plate at the level of the posterior margin of the subcapsular process; the posterior lamina arises from the external surface of that portion of the pila occipitalis that forms the posteroventral wall of the metotic fissure. During ontogeny, both laminae lying in the anteroposterior sequence ossify in membrane, fuse together, grow laterodorsally, and fuse with the lateral wall of the lateral semicircular canal and the crista parotica. This lamina forms a new, secondary wall enclosing the posterior section of the otic capsule and contains the large external jugular foramen (or foramen vagi) in its basal portion. The laminae, designated lamina juxtaotica anterior and posterior (lamina juxtaotica when fused together), have not been recorded previously in crocodylians and are absent in all other Recent reptiles. From the functional point of view, the juxtaotic lamina 1) forms the margins of the external jugular foramen, and 2) forms the floor of the posterior section of the Eustachian tube. In birds, the structure called the metotic cartilage, which arises in ontogeny as an independent element, has a similar position as the juxtaotic lamina. However, the two structures differ in their developmental origins and their relation to the Eustachian tube and the ramus hyomandibularis of the facialis nerve. Moreover, there is no external jugular foramen in birds.     

Cranial skeletogenesis and osteology of the redeye tetra Moenkhausia sanctaefilomenae

The skeletogenesis and osteology of the syncranium of the redeye tetra Moenkhausia sanctaefilomenae is described. Skeletal development is rapid, with many elements of the chondrocranium and splanchnocranium well formed prior to the onset of ossification. The chondrocranium develops from an initial set of cartilaginous precursors, and continued elaboration proceeds from a series of processes which expand and converge to form the floor of the cranial vault, the otic capsule, the supraorbital bridge and the ethmoid region. Prodigious growth is observed for a number of splanchnocranial elements, including the Meckel's cartilage and the ceratohyal cartilage. Ossification occurs in overlapping phases with initial ossification of the jaws and neurocranial floor followed by the splanchnocranium, the supraorbital bridges and the ethmoid and cranial vault. Teeth are observed primarily on the premaxilla and dentary, while a single tooth is present on the maxilla. Particular cartilages, which had originally formed in the early larva, appear to degenerate and have no ossified representative in the adult syncranium. The cranial development for M. sanctaefilomenae is compared to those of other characiforms.     

Morphogenesis of the cranium of Cavia porcellus L. II: Comparative part and literature

The development of the chondrocranium of Cavia porcellus is compared to those of other rodents. The tectum posterius of the investigated rodents is orientated vertically. This position is functionally caused by the attachment of the muscles of the neck and shoulder girdle. The paracondylar process is a typical feature of rodents although absent in Mesocricetus. Only in Cavia and Tatera, the connection between the lamina supraoccipitalis and the auditory capsule-the supraoccipitocapsular commissure-is missing. Youssef's (1966) generalization that the course of the notochord in rodents is of transbasal type cannot be confirmed. In Cavia, the auditory capsule is connected with the occipital region only by the exoccipitocapsular commissure. The connection between auditory capsule and basal plate is established by the alicochlear and the anterior basicapsular commissures. In comparison to other rodents, the number of commissures in Cavia is reduced. In rodents, there is always a subarcuate fossa which in later stages of development is filled out by the flocculus cerebelli. In contrary to Rajtova's (1972a) statement, Cavia shows a suprafacial commissure as all mammals do (Reinbach 1952). As the tegmen tympani is absent in Otomys and Erethizon, it is not a typical rodent feature. The carotid foramen is well developed in Cavia but the internal carotid artery obliterates until the 25 mm CRL-stage. In embryonic rodents, the ala temporalis may have a foramen ovale but not a foramen rotundum. During ontogeny rodents show the ala hypochiasmatica for the attachment of the straight muscles of the eyeball. In Cavia the ala hypochiasmatica develops independently and fuses with the postoptic root of the ala orbitalis in later stages. In myomorphs and sciumorphs, the orbitoparietal and orbitonasal commissures are present. Only in caviomorphs this part of the primary sidewall of the skull is uncomplete. Erethizon, however, shows an orbitonasal commissure whereas in Cavia both commissures are missing. In this respect the guinea-pig resembles the condition of primates. There is no interorbital septum in rodents. The nasal capsule of rodents contains 1 atrioturbinal, 1 maxilloturbinal, 1 nasoturbinal, and at least 3 ethmoturbinals. Due to the strong development of the alveoli of the incisors, the maxilloturbinale is flected in the caviomorphs. The epiphanial foramina are present. The lamina transversalis anterior is continuous with the nasal septum so that there is a complete zona anularis in rodents. The paraseptal cartilages are continuous with the lamina transversalis anterior but not with the lamina transversalis posterior.(ABSTRACT TRUNCATED AT 400 WORDS)     

The development of the clavicle in man

The development of the human clavicle was studied in 50 to 60 d old human embryos. Our findings are summarized as follows: The whole clavicle develops from a cartilaginous anlage. In the middle part of the clavicle, an osseus cuff develops very early by the ossification in the perichondrium. In the lumen of this cuff, a cartilaginous cork persists which is resorbed and replaced by bone and marrow later than in other bones. It is possible that cartilaginous nests may persist in the middle part of the clavicle. In both extremities of the clavicle, the normal enchondral ossification exists as it is described in other anlages. It is difficult to explicate the syndrome of the cleido-facial and cleido-cranial dysostoses only as disturbances of the endesmal ossification.     

Braincase evolution in suchian archosaurs (Reptilia: Diapsida): evidence from the rauisuchian Batrachotomus kupferzellensis

The osteology of an almost complete braincase of the rauisuchian archosaur Batrachotomus kupferzellensis Gower from the Middle Triassic of Germany is described. There is a possibly discrete epiotic ossification, the metotic fissure is undivided by bone (i.e. there is a metotic foramen), the medial wall of the otic capsule is mostly ossified, the cerebral branch of the internal carotid artery entered the lateral surface of the parabasisphenoid, the ventral ramus of the opisthotic is more prominent laterally than a strong subvertical ridge on the exoccipital and basioccipital that lies posterior to the external foramen for the hypoglossal nerve, and the perilymphatic foramen faces away from the otic capsule in a posterior direction. Braincase morphology in the rauisuchians Saurosuchus galilei , Postosuchus kirkpatricki, and Tikisuchus romeri is reviewed. A matrix of 27 braincase characters for 12 archosaurian taxa is analysed. The most parsimonious hypothesis is consistent with the currently orthodox view of archosaurian phylogeny, except in that aetosaurians are more closely related to crocodylomorphs than is any rauisuchian. This phylogeny is used in a brief interpretation of the evolution of derived braincase features present in extant crocodilians. © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society , 2002, 136 , 49–76.     

The development of the chondrocranium of the lacertid lizard,Acanthodactylus boskiana

The trabeculae cranii are at first quite separate from each other, after few days their anterior two fifths are connected by a trabecular plate which is obliterated throughout development. The paired origin of the parachordal plate is not observed. The fused posterior orbital cartilages chondrify in the form of a wide short plate, traversed by the oculomotor and trochlear nerves. The basicranial fenestra and fenestra ovalis are formed by the degeneration of pre-existing cartilage. The cochlear portion is completely fused with the parachordal plate from the very beginning. The elements of the pterygoquadrate are fused together. The quadrate and Meckel's cartilage are in close contact from the very beginning. While the lower part of the interorbital septum is derived from the trabecula communis, its upper part is derived from the anterior orbital cartilages. The lateral parts of the fused posterior orbital cartilages give rise to most of the taeniae and pilae of the orbitotemporal region. There is only one commissure between the auditory capsule and parachordal plate. A cartilaginous connection between the distal portion of the columella auris and ceratohyal persists for some time. The parietotectal and paranasal cartilages are fused together from the very beginning. The processus paroticus originates from the columella auris. In the fully formed stage the notochord is completely embedded in the occipital condyle. The union between the condyle and odontoid process persists. The auditory capsules and occipital arches contribute to the formation of the tectum synoticum plus posterius. The prefacial commissure and facial foramen lie in front of the cochlear portion. The columella auris possesses a processus internus (connected with the quadrate), but the processes a dorsalis has completely disappeared. The orbitotemporal region is quite complete. A medial fenestra is formed in the planum supraseptale. A fenestra is observed in each of the interorbital and nasal septa. The lamina transversalis anterior is fused with the parietotectal cartilage. A complete zona annularis is present. The outer wall of the paranasal cartilage is perforated by a large fenestra lateralis. The parietotectal and paranasal cartilages and the posterior process of the lamina transversalis anterior contribute to the formation of the concha nasalis. There is a contact between the planum antorbitale and nasal septum. The pterygoid process has disappeared. The common characters of the lacertid chondrocranuium are deduced.     

Morphogenesis of the cranium of Cavia porcellus L. I: Introduction, classification and descriptive part

The craniogenesis of Cavia porcellus has been investigated in 7 embryos of different ages. From the developmental stage of 36 mm CRL, a reconstruction of the chondrocranium is described. As there is still a gap in the tectum posterius, the foramen magnum is not closed posteriorly. The course of the notochord is retrobasilar at the beginning, more rostrally it runs intrabasilar. After ossification, the place where the notochord enters the basioccipital is marked by a cavity. This cavity is not identical with the posterior basicranial fenestra. The laminae alares build up strong paracondylar processes. The auditory capsule is connected with the occipital region only by the exoccipitocapsular commissure, but there is no supraoccipitocapsular commissure. The fossa subarcuata is pierced by a subarcuate foramen. The very short lamina parietalis is not in contact with the orbital wing as there is no orbitoparietal commissure. The processus recessus divides the perilymphatic foramen into fenestra rotunda and aquaeductus cochleae. The suprafacial commissure arises from the upper margin of the canalicular part of the auditory capsule, but it does not reach the superior surface of the cochlear part at this stage. The tegmen tympani is well developed. The foramen singulare is not yet separated from the inferior acoustic foramen. At the stage of 36 mm CRL there is no septum spirale cartilagineum. Mm. tensor tympani et stapedius are developed in the typical way. The auditory capsule is connected with the basal plate by the anterior basicochlear and the alicochlear commissures. The floor of the orbitotemporal region is incomplete, the temporal wings are small. The alicochlear commissure, the alar process, the anterior basicochlear commissure, and the basal plate surround the carotid foramen, but there is no blood vessel passing through it. The temporal wing is at the beginning of ossification and shows a fissura ovalis for the mandibular nerve. Although the hypophysial canal is still present, there are no structures passing through it. There is no foramen rotundum. The orbital wing is still cartilagineous. The basal plate and the pre- and postoptic roots border the optical foramen. The straight muscles of the eyeball are attached to the ala hypochiasmatica which projects from the postoptic root. The interorbital septum is absent. The ophthalmic artery, which instead of the obliterated internal carotid artery, contributes to the circulus arteriosus cerebri is well developed. There is no orbitonasal commissure . The epiphanial foramina are present.(ABSTRACT TRUNCATED AT 400 WORDS)     

Distinct spatiotemporal roles of hedgehog signalling during chick and mouse cranial base and axial skeleton development

The cranial base exerts a supportive role for the brain and includes the occipital, sphenoid and ethmoid bones that arise from cartilaginous precursors in the early embryo. As the occipital bone and the posterior part of the sphenoid are mesoderm derivatives that arise in close proximity to the notochord and floor plate, it has been assumed that their development, like the axial skeleton, is dependent on Sonic hedgehog (Shh) and modulation of bone morphogenetic protein (Bmp) signalling. Here we examined the development of the cranial base in chick and mouse embryos to compare the molecular signals that are required for chondrogenic induction in the trunk and head. We found that Shh signalling is required but the molecular network controlling cranial base development is distinct from that in the trunk. In the absence of Shh, the presumptive cranial base did not undergo chondrogenic commitment as determined by the loss of Sox9 expression and there was a decrease in cell survival. In contrast, induction of the otic capsule occurred normally demonstrating that induction of the cranial base is uncoupled from formation of the sensory capsules. Lastly, we found that the early cranial mesoderm is refractory to Shh signalling, likely accounting for why development of the cranial base occurs after the axial skeleton. Our data reveal that cranial and axial skeletal induction is controlled by conserved, yet spatiotemporally distinct mechanisms that co-ordinate development of the cranial base with that of the cranial musculature and the pharyngeal arches.     

The cranial development of Elaphe obsoleta (Ophidia,colubridae)

The kinetic skull of snakes is a highly specialized structure that has allowed these limbless organisms to exploit a wide variety of habitats. Here we analyze the development of the cranium in the colubrid snake Elaphe obsoleta quadrivittata based on two sets of embryos raised under controlled conditions and preserved at regular intervals during embryogenesis. Emphasis is on the interactions between dermal and endochondral ossification in the basicranium and in the posterior orbitotemporal region. In Elaphe, the laterosphenoid initially develops as an ascending process of the basal plate and is a combination of membrane and cartilage bone. The maxilla shows a peculiar pattern of differentiation from several centers of ossification.     

Distribution and expression of two interactive extracellular matrix proteins, cytotactin and cytotactin-binding proteoglycan, during development of Xenopus laevis. I. Embryonic development.

An immunohistochemical study of the localization of cytotactin and cytotactin-binding (CTB) proteoglycan throughout embryonic development of the anuran Xenopus laevis reveals that both appear in a restricted pattern related to specific morphogenetic events. CTB proteoglycan expression is first detected during gastrulation at the blastopore lip. Later, it is seen in the archenteron roof around groups of cells forming the notochord, somites and neural plate. Cytotactin first appears after neurulation, and is restricted to the intersomitic regions. Both molecules appear along the migratory pathways of neural crest cells in the trunk and tail. Later, cytotactin is present at sites where neural crest cells differentiate, around the aorta and in the smooth muscle coat of the gut; CTB proteoglycan is absent from these sites. In the head, cytotactin is initially restricted to the regions between cranial somites, while CTB proteoglycan is distributed throughout the cranial mesenchyme. The expression of both molecules is later associated with key events in chondrogenesis during the development of the skull. After chondrogenesis, CTB proteoglycan is distributed throughout the cartilage matrix, while cytotactin is restricted to a thin perichondrial deposit. Both molecules are expressed in developing brain. These findings are compared to studies of the chick embryo and although distinct anatomical differences exist between frog and chick, the expression of these molecules is associated with similar developmental processes in both species. These include mesoderm segmentation, neural crest cell migration and differentiation, cartilage development, and central nervous system histogenesis.     

Early development of the chondrocranium in Chrysichthys auratus

The inception and development of the cartilaginous cephalis skeleton of Chrysichthys auratus is described from hatching to about 18 days post-hatching. At hatching, no skeletal structure is present. Not until day 3 do clearly delimited cranial primordia become apparent. As in many siluriforms, the neurocranium is platybasic from the start, the suspensorium constitutes, with Meckel's cartilage and the hyoid bar, a single cartilaginous element, and the junction between the front and rear of the neurocranium is complete on day 4. By day 8 the quadratomandibular joint has formed and the tectum posterius has appeared. Cartilage reduction first affects the trabecular bars, then, markedly, the visceral arches. By day 18 the braincase floor has almost disappeared.     

Timing of development of the middle ear of Anura (Amphibia)

Summary The opercularis system and tympanum-stapes complex of the anuran middle ear develop at different times relative to metamorphosis. In early larvae, the fenestra ovalis is represented by a large lateral opening in the otic capsule filled with connective tissue. At later larval stages, but well before metamorphosis, a cartilaginous operculum begins to form at the posterior margin of the fenestra ovalis, and proceeds to expand to fill all except the anterior part of the fenestra. The opercularis muscle forms along with the levator scapulae superior muscle at the anteromedial edge of the developing suprascapular cartilage of the shoulder girdle. The muscle fibers extend anteroventrally towards the operculum and otic capsule, and, just before emergence of the forelimbs, that portion that will form the opercularis muscle inserts on the lateral surface of the operculum. At this stage, when the metamorphosing frogs first show terrestrial habits, the opercularis system is complete and presumably functional. Timing of development of the tympanum-stapes complex is more variable. The stapes begins as a cartilaginous condensation in the anterior part of the fenestra ovalis, and develops laterally to eventually contact the epidermis and dermis that together will form the tympanum. Meanwhile a middle ear cavity and tympanic annulus form to complete the complex. In several species, especially those that metamorphose at a smaller body size, the tympanum-stapes complex is quite incomplete by the end of metamorphosis, and in Hyla crucifer it takes about 60 days to fully develop. The presence of a complete opercularis system by the start of terrestrial activity is consistent with an hypothesized seismic function of the system. The independent timing of development of the opercularis system and tympanum-stapes complex does not support functional hypotheses linking the opercularis system with modulation of responsiveness of the tympanum-stapes complex to aerial sound. Newly metamorphosed frogs with poorly developed tympanum-stapes complexes are presumably either insensitive to aerial sound or employ alternate mechanisms for transmission of sound energy to the inner ear, possibly involving the opercularis system.     

Sequence of chondrocranial development in the oriental fire bellied toad Bombina orientalis

The vertebrate head as a major novelty is directly linked to the evolutionary success of the vertebrates. Sequential information on the embryonic pattern of cartilaginous head development are scarce, but important for the understanding of its evolution. In this study, we use the oriental fire bellied toad, Bombina orientalis, a basal anuran to investigate the sequence and timing of larval cartilaginous development of the head skeleton from the appearance of mesenchymal Anlagen in post-neurulation stages until the premetamorphic larvae. We use different methodological approaches like classic histology, clearing and staining, and antibody staining to examine the larval skeletal morphology. Our results show that in contrast to other vertebrates, the ceratohyals are the first centers of chondrification. They are followed by the palatoquadrate and the basihyal. The latter later fuses to the ceratohyal and the branchial basket. Anterior elements like Meckel's cartilage and the rostralia are delayed in development and alter the ancestral anterior posterior pattern observed in other vertebrates. The ceratobranchials I–IV, components of the branchial basket, follow this strict anterior–posterior pattern of chondrification as reported in other amphibians. Chondrification of different skeletal elements follows a distinct pattern and the larval skeleton is nearly fully developed at Gosner Stage 28. We provide baseline data on the pattern and timing of early cartilage development in a basal anuran species, which may serve as guidance for further experimental studies in this species as well as an important basis for the understanding of the evolutionary changes in head development among amphibians and vertebrates.     

Ontogenetic development of an exceptionally preserved Devonian cartilaginous skeleton

Cartilaginous vertebrate skeletons leave few records as fossils, unless mineralized. Here, we report outstanding preservation of early stages of cartilage differentiation, present in the Devonian vertebrate Palaeospondylus gunni. In large specimens of Palaeospondylus, enlarged, hypertrophic cell spaces (lacunae) are dominant in the cartilage matrix, each defined by thin mineralized matrix, where phosphorus and calcium co-occur. This is comparable to living endochondral cartilage, where cell hypertrophy and matrix mineralization mark the end of an ontogenetic process of cell growth and division before bone formation. New information from small individuals of Palaeospondylus demonstrates that the skeleton comprises mostly unmineralized organic matrix with fewer hypertrophic cell spaces, these occurring only in the central regions of each element. Only here has the surrounding matrix begun to mineralize, differing from the larger specimens in that phosphorus is dominant with little associated calcium at these earlier stages. This reflects cellular control of mineralization in living tissues through phosphate accumulation around hypertrophic cells, with later increase in calcium in the cartilaginous matrix. These features are always associated with endochondral bone development, but in the Palaeospondylus skeleton, this bone never develops. This skeletal state is thus far unique among vertebrates, with two alternative explanations: either later stages of endochondral bone development have been lost in Palaeospondylus, or, in a stepwise acquisition of the mineralized skeleton, these late stages have not yet evolved.     

Skull development during anuran metamorphosis: I. Early development of the first three bones to form--the exoccipital, the parasphenoid, and the frontoparietal

In anuran amphibians, cranial bones typically first form at metamorphosis when they rapidly invest or replace the cartilaginous larval skull. We describe early development of the first three bones to form in the Oriental fire-bellied toad, Bombina orientalis--the parasphenoid, the frontoparietal, and the exoccipital--based on examination of serial sections. Each of these bones is fully differentiated by Gosner stage 31 (hindlimb in paddle stage) during premetamorphosis. This is at least six Gosner developmental stages before they are first visible in whole-mount preparations at the beginning of prometamorphosis. Thus, developmental events that precede and mediate the initial differentiation of these cranial osteogenic sites occur very early in metamorphosis--a period generally considered to lack significant morphological change. Subsequent development of these centers at later stages primarily reflects cell proliferation and calcified matrix deposition, possibly in response to increased circulating levels of thyroid hormone which are characteristic of later metamorphic stages. Interspecific differences in the timing of cranial ossification may reflect one or both of these phases of bone development. These results may qualify the use of whole-mount preparations for inferring the sequence and absolute timing of cranial ossification in amphibians.