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Abstract Several studies describe the development of the chondrocranium of vertebrates. The details in these studies vary a lot, which makes it hard to compare developmental patterns and identify evolutionary trends. Therefore, we aim to close this gap for anurans, which is the largest order of amphibians. We present here a detailed description of the chondrocranium morphology and development of Smilisca phaeota, the New Granada cross-banded tree frog. The anatomy was described for the larvae at or older than Gossner stage 31 and before ossification starts. Following this, we describe the development of the chondrocranium from Gossner stages 19–26. Early in Gossner stage 19 no precursors of any cartilages are visible, while later in that stage the mesodermal Anlage of Meckel’s cartilage was observed. In the subsequent stages more and more mesodermal anlagen become identifiable, followed by chondrification, and final differentiation of the cartilage elements. We used serial sections to study all the developmental stages and additionally utilized cleared and stained specimens and CT scan data. The latter were also used for the 3D reconstruction of the chondrocranium. We previously studied several species and compared these developmental patterns with S. phaeota, revealing potentially characteristic patterns significant for Lalagobatrachia, a clade that includes over 7000 frog species. These include (1) the suprarostral alae develop before the suprarostral corpus, (2) the infrarostral cartilage chondrifies late, after the chondrification of ceratobranchial 1, and (3) the ceratohyal body is the first element to show chondrocytes and to chondrify. However, with only six species studied so far, our data only provide a basis for future studies and developing hypotheses about the ancestral developmental pattern in anurans.

Several studies describe the development of the chondrocranium of vertebrates. The details in these studies vary a lot, which makes it hard to compare developmental patterns and identify evolutionary trends. Therefore, we aim to close this gap for anurans, which is the largest order of amphibians. We present here a detailed description of the chondrocranium morphology and development of Smilisca phaeota, the New Granada cross-banded tree frog. The anatomy was described for the larvae at or older than Gossner stage 31 and before ossification starts. Following this, we describe the development of the chondrocranium from Gossner stages 19–26. Early in Gossner stage 19 no precursors of any cartilages are visible, while later in that stage the mesodermal Anlage of Meckel's cartilage was observed. In the subsequent stages more and more mesodermal anlagen become identifiable, followed by chondrification, and final differentiation of the cartilage elements. We used serial sections to study all the developmental stages and additionally utilized cleared and stained specimens and CT scan data. The latter were also used for the 3D reconstruction of the chondrocranium. We previously studied several species and compared these developmental patterns with S. phaeota, revealing potentially characteristic patterns significant for Lalagobatrachia, a clade that includes over 7000 frog species. These include (1) the suprarostral alae develop before the suprarostral corpus, (2) the infrarostral cartilage chondrifies late, after the chondrification of ceratobranchial 1, and (3) the ceratohyal body is the first element to show chondrocytes and to chondrify. However, with only six species studied so far, our data only provide a basis for future studies and developing hypotheses about the ancestral developmental pattern in anurans. [ABSTRACT FROM AUTHOR]

The article is devoted to the osteology of the lake minnow – an indigenous representative of the ichthyofauna of Kazakhstan. This species has a wide range in northern Eurasia and a debatable taxonomic structure. The generic status of the lake minnow has changed several times - currently it is often assigned to the genus Rhynchocypris. Within this species, several subspecies have been described, two of which live in the water bodies of Northern and Central Kazakhstan. Modern information on the lake minnow from the Northern Kazakhstan is limited to morphometric data, on the basis of which it is assigned to the nominative subspecies R. p. percnurus. Another form, previously described as a subspecies of R. czekanowskii from Northern Kazakhstan, was subsequently considered as a subspecies of the lake minnow R. p. ignatowi, which also inhabits the water bodies of Central Kazakhstan. Its systematic status remains unclear, and available data on morphology and distribution are scarce. The purpose of this study was to identify the characteristic features and interpopulation variability of the visceral skull bones of the lake minnow from the water bodies of Northern and Central Kazakhstan. The research material consisted of fish from populations of the Kylshakty River (Northern Kazakhstan) and the Karkaraly River (Central Kazakhstan). Using the method of preparing and staining skeletons, osteological preparations of fish from both populations were obtained. As a result of the analysis of osteological characteristics, the bones of the viscerocranium of the lake minnow from the water bodies of Kazakhstan were characterized in detail for the first time. Characteristic features of the shape of the maxillary, dentary, opercular, basihyal and pharyngeal bones were revealed. Interpopulation differences concern the shape of the basihyal and the third epibranchial, as well as the presence or absence of the first pharyngobranchial. The data obtained may indicate the morphological distinctiveness of the populations of Northern and Central Kazakhstan. [ABSTRACT FROM AUTHOR]

The craniofacial skeleton of vertebrates is a major innovation of the whole clade. Its development and composition requires a precisely orchestrated sequence of chondrification events which lead to a fully functional skeleton. Sequential information on the precise timing and sequence of embryonic cartilaginous head development are available for a growing number of vertebrates. This enables a more and more comprehensive comparison of the evolutionary trends within and among different vertebrate clades. This comparison of sequential patterns of cartilage formation enables insights into the evolution of development of the cartilaginous head skeleton. The cartilaginous sequence of head formation of three basal anurans (Xenopus laevis, Bombina orientalis, Discoglossus scovazzi) was investigated so far. This study investigates the sequence and timing of larval cartilaginous development of the head skeleton from the appearance of mesenchymal Anlagen until the premetamorphic larvae in the neobatrachian species Bufo bufo. Clearing and staining, histology, and 3D reconstruction enabled the tracking of 75 cartilaginous structures and the illustration of the sequential changes of the skull as well as the identification of evolutionary trends of sequential cartilage formation in the anuran head. The anuran viscerocranium does not chondrify in the ancestral anterior to posterior direction and the neurocranial elements do not chondrify in posterior to anterior direction. Instead, the viscerocranial and neurocranial development is mosaic‐like and differs greatly from the gnathostome sequence. Strict ancestral anterior to posterior developmental sequences can be observed within the branchial basket. Thus, this data is the basis for further comparative developmental studies of anuran skeletal development. Research highlights: The anuran viscerocranium develops mosaic‐like.Posterior neurocranial elements extend anteriorly and anterior elements extend posteriorly.Posterior to anterior growth of the parachordal and initial development of the lateral wall of the otic capsule are shared gnathostome features. [ABSTRACT FROM AUTHOR]

Fibroblast growth factor (Fgf) signaling regulates many processes during development. In most cases, one tissue layer secretes an Fgf ligand that binds and activates an Fgf receptor (Fgfr) expressed by a neighboring tissue. Although studies have identified the roles of specific Fgf ligands during development, less is known about the requirements for the receptors. We have generated null mutations in each of the five fgfr genes in zebrafish. Considering the diverse requirements for Fgf signaling throughout development, and that null mutations in the mouse Fgfr1 and Fgfr2 genes are embryonic lethal, it was surprising that all zebrafish homozygous mutants are viable and fertile, with no discernable embryonic defect. Instead, we find that multiple receptors are involved in coordinating most Fgf-dependent developmental processes. For example, mutations in the ligand fgf8a cause loss of the midbrain-hindbrain boundary, whereas, in the fgfr mutants, this phenotype is seen only in embryos that are triple mutant for fgfr1a;fgfr1b;fgfr2, but not in any single or double mutant combinations. We show that this apparent fgfr redundancy is also seen during the development of several other tissues, including posterior mesoderm, pectoral fins, viscerocranium, and neurocranium. These data are an essential step toward defining the specific Fgfrs that function with particular Fgf ligands to regulate important developmental processes in zebrafish.

Simple Summary: The comparison of anatomical characters is scarcely investigated in domestic animal breeds, and the racial classification has been based on morphological descriptions of the cranial region as a unit. The aim was to study the basicranial organization of the neurocranium and splanchnocranium modules in a sample of 31 skulls of adult Araucanian horses using 2D morphometric geometric techniques. Thirty-one reference points were used. The RV coefficient (the multivariate analog of a correlation) was estimated to analyze the independence of these two parts, as well as their morphological integration, using a two-block least squares analysis. The study results confirm the modular development of the neurocranium and the splanchnocranium, the former being more stable than the latter as well as low morphological integration between the two. The development between both parties is structured in a modular way but allows relative independence. Now it would be interesting for future studies to add muscles (those that connect the cranial parts, but also the cervical), the hyoid apparatus, and the ossicles of the internal ear and the jaw and analyze if they behave as integrated modules between them. The skull is divided into neurocranium and splanchnocranium, and its variation allows ecomorphological studies to learn about possible evolutionary and adaptive characteristics. The basicranial organization of the neurocranium and splanchnocranium modules was studied in a sample of 31 skulls from adult Araucanian horses by means of 2D geometric morphometric techniques. The neurocranium and splanchnocranium modules on the ventral aspect were analyzed separately using a set of 31 landmarks. The RV coefficient (the multivariate analog of a correlation) was estimated to analyze the independence of these two parts, as well as their morphological integration, using a two-block analysis of least squares. The study results confirm the modular development of the neurocranium and the splanchnocranium, the former being more stable than the latter as well as low morphological integration between the two. The development between both parties is structured in a modular way but allows relative independence. Now it would be interesting for future studies to add muscles (those that connect the cranial parts, but also the cervical), the hyoid apparatus, and the ossicles of the internal ear and the jaw and analyze if they behave as integrated modules between them. Since this research has been conducted at the subspecific breed level, it could be plausible that in other breeds, this integrative development was different. [ABSTRACT FROM AUTHOR]

Abstract Background The craniofacial skeleton is an evolutionary innovation of vertebrates. Due to its complexity and importance to protect the brain and aid in essential functions (e.g., feeding), its development requires a precisely tuned sequence of chondrification and/or ossification events. The comparison of sequential patterns of cartilage formation bears important insights into the evolution of development. Discoglossus scovazzi is a basal anuran species. The comparison of its chondrocranium (cartilaginous neuro- & viscerocranium) development with other basal anurans (Xenopus laevis, Bombina orientalis) will help establishing the ancestral pattern of chondrification sequences in anurans and will serve as basis for further studies to reconstruct ancestral conditions in amphibians, tetrapods, and vertebrates. Furthermore, evolutionary patterns in anurans can be studied in the light of adaptations once the ancestral sequence is established. Results We present a comprehensive overview on the chondrocranium development of D. scovazzi. With clearing and staining, histology and 3D reconstructions we tracked the chondrification of 44 elements from the first mesenchymal Anlagen to the premetamorphic cartilaginous head skeleton and illustrate the sequential changes of the skull. We identified several anuran and discoglossoid traits of cartilage development. In D. scovazzi the mandibular, hyoid, and first branchial arch Anlagen develop first followed by stepwise addition of the branchial arches II, III, and IV. Nonetheless, there is no strict anterior to posterior chondrification pattern within the viscerocranium of D. scovazzi. Single hyoid arch elements chondrify after elements of the branchial arch and mandibular arch elements chondrify after elements of the branchial arch I. Conclusions In Osteichthyes, neurocranial elements develop in anterior to posterior direction. In the anurans investigated so far, as well as in D. scovazzi, the posterior parts of the neurocranium extend anteriorly, while the anterior parts of the neurocranium, extend posteriorly until both parts meet and fuse. Anuran cartilaginous development differs in at least two crucial traits from other gnathostomes which further supports the urgent need for more developmental investigations among this clade to understand the evolution of cartilage development in vertebrates.

The vertebrate head and its skull represent a significant innovation that has played a key role in the evolutionary and ecological success of vertebrates. For a global and integral understanding of the evolution of the head skeleton, it is essential to have reliable information on the development of chondrocranium in a wide range of vertebrate species. Therefore, we studied the cranial chondrogenesis of the larva of the Budgett frog, Lepidobatrachus laevis (Ceratophryidae, Neobatrachia). We studied the development using several methods, including histological preparation of transverse sections of the chondrocranium, morphological analysis of three different states of development (mesenchymal aggregation, differentiation, and chondrification), and three-dimensional digital reconstructions. As a result, we observed that the Anlage of the chondrocranium at Gosner stage 19 is laterally compressed, that is, it is initially higher than wide. It gradually flattens, enlarges, and differentiates until reaching a very wide and flat shape at Gosner stage 26. Furthermore, we show that the chondrocranial development of L. laevis takes place in a mosaic pattern, which differs to nontetrapod vertebrates in which an anterior to posterior gradient of chondrification is observed. We identified 19 developmental stages in L. laevis according to the chondrification state of its cranial structures. The first element reaching the differentiation-into-chondroblast stage is the hypobranchial plate of the branchial basket, and chondrification, that is, final differentiation, occurs simultaneously in several structures of the neurocranium and viscerocranium. We hypothesize that the rapid chondrification of L. laevis' chondrocranium is an adaptation to the semi-arid climate conditions from its type locality, El Gran Chaco in South America. Due to the only temporary availability of suitable water accumulations this apparent accelerated development would make sense to ensure the tadpoles are froglets by the time the water body disappears. Here, we provide novel information on chondrocranial development in L. laevis. We compare our results to the developmental sequences, previously known from other vertebrate taxa, particularly within the amphibian phylogeny, in an attempt to understand developmental variability and the evolutionary history of the vertebrate head skeleton., (© 2024 The Author(s). The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Simple Summary: Sex estimation is a crucial step in the identification of unknown bone remains. The accuracy of sex estimation methods depends on the level of sexual dimorphism manifested by the human bones. Therefore, the evaluation of sex differences of particular bones of the skeleton is an important preceding stage. We have used geometric morphometric techniques to investigate the sexual dimorphism in the size and shape of the facial part of the skull and its subregions. Our results show that the facial skeleton in males and females differs more in size than in shape, so its overall size is a more useful sex indicator than its shape. The same result is observed for all facial subregions studied here. However, the best discrimination between the male and female skulls is achieved when both size and shape are considered together. The level of sexual dimorphism manifested by human bones is an important factor for development of effective sex estimation methods. The aim of the study was to investigate the sexual dimorphism in the size and shape of the viscerocranium using geometric morphometric techniques. It also aimed to explore the sex differences in distinct viscerocranial regions and to establish the most dimorphic region with regard to size and shape. Computed tomography images of 156 males and 184 females were used in the study. Three-dimensional coordinates of 31 landmarks were acquired. Five landmark configurations were constructed from the viscerocranium and its orbital, nasal, maxillary, and zygomatic region. Generalized Procrustes superimposition, principal component analysis, and discriminant analysis were applied to each configuration. The significance of the sex differences in size and shape was assessed and significant differences were found in all configurations. The highest accuracy was obtained from both shape and size of the whole viscerocranium. Based on size only, the highest accuracy was achieved by the nasal region. The accuracy based on shape was generally low for all configurations, but the highest result was attained by the orbital region. Hence, size is a better sex discriminator than shape. [ABSTRACT FROM AUTHOR]

Ciliopathies are genetic syndromes that link skeletal dysplasias to the dysfunction of primary cilia. Primary cilia are sensory organelles synthesized by intraflagellar transport (IFT)—A and B complexes, which traffic protein cargo along a microtubular core. We have reported that the deletion of the IFT-A gene, Thm2, together with a null allele of its paralog, Thm1, causes a small skeleton with a small mandible or micrognathia in juvenile mice. Using micro-computed tomography, here we quantify the craniofacial defects of Thm2−/−; Thm1aln/+ triple allele mutant mice. At postnatal day 14, triple allele mutant mice exhibited micrognathia, midface hypoplasia, and a decreased facial angle due to shortened upper jaw length, premaxilla, and nasal bones, reflecting altered development of facial anterior-posterior elements. Mutant mice also showed increased palatal width, while other aspects of the facial transverse, as well as vertical dimensions, remained intact. As such, other ciliopathy-related craniofacial defects, such as cleft lip and/or palate, hypo-/hypertelorism, broad nasal bridge, craniosynostosis, and facial asymmetry, were not observed. Calvarial-derived osteoblasts of triple allele mutant mice showed reduced bone formation in vitro that was ameliorated by Hedgehog agonist, SAG. Together, these data indicate that Thm2 and Thm1 genetically interact to regulate bone formation and sculpting of the postnatal face. The triple allele mutant mice present a novel model to study craniofacial bone development. [ABSTRACT FROM AUTHOR]

Background: The craniofacial skeleton is an evolutionary innovation of vertebrates. Due to its complexity and importance to protect the brain and aid in essential functions (e.g., feeding), its development requires a precisely tuned sequence of chondrification and/or ossification events. The comparison of sequential patterns of cartilage formation bears important insights into the evolution of development. Discoglossus scovazzi is a basal anuran species. The comparison of its chondrocranium (cartilaginous neuro- & viscerocranium) development with other basal anurans (Xenopus laevis, Bombina orientalis) will help establishing the ancestral pattern of chondrification sequences in anurans and will serve as basis for further studies to reconstruct ancestral conditions in amphibians, tetrapods, and vertebrates. Furthermore, evolutionary patterns in anurans can be studied in the light of adaptations once the ancestral sequence is established. Results: We present a comprehensive overview on the chondrocranium development of D. scovazzi. With clearing and staining, histology and 3D reconstructions we tracked the chondrification of 44 elements from the first mesenchymal Anlagen to the premetamorphic cartilaginous head skeleton and illustrate the sequential changes of the skull. We identified several anuran and discoglossoid traits of cartilage development. In D. scovazzi the mandibular, hyoid, and first branchial arch Anlagen develop first followed by stepwise addition of the branchial arches II, III, and IV. Nonetheless, there is no strict anterior to posterior chondrification pattern within the viscerocranium of D. scovazzi. Single hyoid arch elements chondrify after elements of the branchial arch and mandibular arch elements chondrify after elements of the branchial arch I. Conclusions: In Osteichthyes, neurocranial elements develop in anterior to posterior direction. In the anurans investigated so far, as well as in D. scovazzi, the posterior parts of the neurocranium extend anteriorly, while the anterior parts of the neurocranium, extend posteriorly until both parts meet and fuse. Anuran cartilaginous development differs in at least two crucial traits from other gnathostomes which further supports the urgent need for more developmental investigations among this clade to understand the evolution of cartilage development in vertebrates. [ABSTRACT FROM AUTHOR]

The skull is divided into neurocranium and splanchnocranium, and its variation allows ecomorphological studies to learn about possible evolutionary and adaptive characteristics. The basicranial organization of the neurocranium and splanchnocranium modules was studied in a sample of 31 skulls from adult Araucanian horses by means of 2D geometric morphometric techniques. The neurocranium and splanchnocranium modules on the ventral aspect were analyzed separately using a set of 31 landmarks. The RV coefficient (the multivariate analog of a correlation) was estimated to analyze the independence of these two parts, as well as their morphological integration, using a two-block analysis of least squares. The study results confirm the modular development of the neurocranium and the splanchnocranium, the former being more stable than the latter as well as low morphological integration between the two. The development between both parties is structured in a modular way but allows relative independence. Now it would be interesting for future studies to add muscles (those that connect the cranial parts, but also the cervical), the hyoid apparatus, and the ossicles of the internal ear and the jaw and analyze if they behave as integrated modules between them. Since this research has been conducted at the subspecific breed level, it could be plausible that in other breeds, this integrative development was different.

Palatine is a cranial bone very less studied in comparative veterinary anatomy. In our study, we performed the comparison of this bone between sheep (Ovis aries L., 1758) and goat (Capra hircus L., 1758), from a sample of 36 and 17 skulls respectively, using methods of geometric morphology. A total of 32 points (4 landmarks and 28 semi-landmarks) were chosen to analyse the horizontal lamina of the palatine bone. Statistically significant differences were reflected for both size and shape. Capra denotes a clear lateral expansion of the bone and rostral and a central contraction, with a relative approach of palatine foramina, while in Ovis foramina are more laterally distant. In our view, this greater width of the horizontal lamina in Capra would be explained by a greater capacity to rub the food compared to Ovis. [ABSTRACT FROM AUTHOR]

This study aimed to determine the development time of the sutures and foramina of the skull in fetuses of 350 sheep obtained from Northern Nigerian abattoirs. They were separated into 7 age groups and their heads collected and processed using the Alizarin technique. A total of 12 neurocranial sutures were observed in the first and second trimesters; 5 and 7 neurocranial and viscerocranial sutures respectively. In the neurocranium, the cornual and interfrontal sutures were established at 48th-50th day and 51st-53rd days of gestation respectively, whereas the occipital sutures were both identified at 61st-67th days of gestation. The anterior fontanelle appeared in the second trimester, although earlier in Yankasa than in Balami and Uda breeds. However, the posterior fontanelle, interparieto-parietal sutures, and lambdoid sutures were absent. In the viscerocranium, the zygomaticomaxillary and maxilloincisive sutures appeared on the 45th-47th days. The frontonasal sutures were seen on the 54th-56th days; the lacrimomaxillary sutures, lacrimozygomatic sutures, and frontolacrimal sutures appeared on the 61st-67th days. In the 3 breeds, the suture formation occurs at a similar time interval; sutural development is slower in the neurocranium than the viscerocranium; and intrasutural closure of the cornual, interfrontal, frontonasal, zygomaticomaxillary, and maxilloincisive sutures occur as early as the second trimester. [ABSTRACT FROM AUTHOR]

Ciliopathies are genetic syndromes that link skeletal dysplasias to the dysfunction of primary cilia. Primary cilia are sensory organelles synthesized by intraflagellar transport (IFT)—A and B complexes, which traffic protein cargo along a microtubular core. We have reported that the deletion of the IFT-A gene, Thm2, together with a null allele of its paralog, Thm1, causes a small skeleton with a small mandible or micrognathia in juvenile mice. Using micro-computed tomography, here we quantify the craniofacial defects of Thm2−/−; Thm1aln/+ triple allele mutant mice. At postnatal day 14, triple allele mutant mice exhibited micrognathia, midface hypoplasia, and a decreased facial angle due to shortened upper jaw length, premaxilla, and nasal bones, reflecting altered development of facial anterior-posterior elements. Mutant mice also showed increased palatal width, while other aspects of the facial transverse, as well as vertical dimensions, remained intact. As such, other ciliopathy-related craniofacial defects, such as cleft lip and/or palate, hypo-/hypertelorism, broad nasal bridge, craniosynostosis, and facial asymmetry, were not observed. Calvarial-derived osteoblasts of triple allele mutant mice showed reduced bone formation in vitro that was ameliorated by Hedgehog agonist, SAG. Together, these data indicate that Thm2 and Thm1 genetically interact to regulate bone formation and sculpting of the postnatal face. The triple allele mutant mice present a novel model to study craniofacial bone development.

In this study, it was aimed to investigate viscerocranium bones in black-bird (Turdus merula) bird macro-anatomically. In this research, regardless of gender, skulls of seven male and five female adult blackbirds were examined macro-anatomically by maceration. Splanchnocranium bones constituted of lacrimal, nasal, incisive, maxilla, zygomatic, palatine, vomer, quadratum, mandible and hyoid bones. Ethmoid bone was included in the splanchnocranium part by the pressure of orbita. Lacrimal bone was found to be oval and blunt ended. It was seen that nasal bone determines dorsal and lateral borders of the cavum nasi and also nostrils are formed at the end of fusion of extensions constituted together with intermaxillae and nasal bone. It was determined that proc. palatinus of maxilla bone contribute to the shape of palate. Zygomatic bone was also a thin, long, rod-shaped bone formed by the fusion of os jugale and os quadratatojugale, while os vomer was present as a nucleus in this region. It was seen that the mandibula shaped the skeleton of the lower jaw and this bone is formed by incorporating os angulare, os articulare, os supraangulare, os complamentare, os oparculare and os dentale bones. It was observed that the basihyoideum forming the body of the os hyoid bone was rod shaped. It was concluded that data obtained in this study would contribute to the lack of information in this area and it might be a source for systematic field researchers to use in taxonomy. [ABSTRACT FROM AUTHOR]

The avian viscerocranium has been described by several investigators. It was perceived that a review on the ontogeny of the avian viscerocranium would be very useful to enrich the knowledge on this subject. The present article casts light on the avian viscerocranium starting from the early stages up to fairly late ones.

ABSTRACT We document for the first time the early ontogeny of Centropomus poeyi based on captive raised material representing 0-19 days posthatch (dph). The achievement of early developmental landmarks (i.e., yolk-sac depletion, flexion, development of fins) and changes in pigmentation are described (1.4 mm NL-10.6 mm SL; 0-19 dph) and documented for a subset of individuals using high quality photographs. The ontogeny of the viscerocranium is also described (2.4 mm NL-10.6 mm SL; 6-19 dph). Development in C. poeyi occurs over a short period with attainment of the juvenile stage (i.e., full complement of fin rays present in each fin) occurring by 6.9 mm SL. The ontogeny of external pigmentation in C. poeyi is marked by two trends throughout growth: (1) a decrease in pigmentation dorsally; and (2) an increase in pigmentation ventrally along the midline. Development of the viscerocranium begins with the appearance of the maxilla and dentary in individuals of 2.4 mm NL, coinciding with the depletion of the yolk-sac. By 10.6 mm SL all bones of the viscerocranium are present and teeth are present on all teeth-bearing bones of the adult. Aspects of early development in C. poeyi are compared with the congeners C. undecimalis and C. parallelus.

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The present article shows the following points: The quadrate and Meckel’s cartilages have separate centres of chondrification. A symphsis Meckelii is absent. Meckel’s cartilage has three processes. These are processus mandibularis externus, processus mandibularis internus and retroarticularis. The quadrate cartilage has five processes; orbitalis, medialis, lateralis, oticus and the ventral articular processes. The columella auris has two centres of chondrification, a medial otostapedial centre (the stapes) and a lateral hyostapedial centre.

Objective: Craniofacial abnormalities are one of the most common birth defects; among these are defects in jaw bone length. Micro- and macro-gnathia negatively affect quality of life by interfering with mastication, breathing and speech, but the only available treatment option is multiple invasive surgeries, making pharmacological interventions highly desirable. Previous data from our lab has demonstrated a developmental role for altering the differentiation of bone-resorbing osteoclasts in establishing lower jaw length. The aim of this study was to determine the effect of inhibiting only the activity of proteolytic enzymes secreted by active osteoclasts on establishing lower jaw bone length. Methods: Quail (Coturnix coturnix japonica) embryos were given a single dose of an inhibitor or vehicle at a developmental stage when viscerocranium bone deposition is beginning to occur. At a developmental stage when the viscerocranium is largely calcified, the heads were collected, scanned via microcomputed tomography and reproducible landmarks were placed on 3D-reconstructed skulls. Results: Approximately half of the quail given either an inhibitor of matrix metalloproteinase-9 (iMMP9) or cathepsin K (iCTSK) demonstrated an overt lower jaw phenotype, characterized by longer lower jaw bones and a greater lower to upper jaw ratio than control treated embryos. Additionally, iMMP9-treated embryos exhibited a significantly shorter midface length and iCTSK-treated embryos had significantly longer nasal bone length. Conclusion: Our data suggest manipulating bone resorption through pharmacological modulation of osteoclast activity by proteolytic enzymes may be a potential option for altering lower jaw length developmentally. [ABSTRACT FROM AUTHOR]

We explored modularity and morphological integration of the ventral cranium during postnatal ontogeny in Martino's vole (Dinaromys bogdanovi). Two closely related phylogenetic groups, originating from the Central and Southeastern part of the species range in the western Balkans, were considered. As expected, both phylogroups had similar patterns of ontogenetic changes in cranial size and shape variation, modularity and integration. At the level of within individual variation, the hypothesis that the viscerocranial and neurocranial regions are separate modules was rejected, indicating that the hypothesized modules are not developmental, but rather functional. At the level of among individual variation, the viscerocranium and the neurocranium could not be recognized as separate modules at the juvenile stage. The strength of association between the hypothesized modules becomes lower with age which finally results in a clear 2-module organization of the ventral cranium at the adult stage. On the other hand, patterns of morphological integration for the cranium as a whole, the viscerocranium and the neurocranium stay consistent across ontogenetic stages. The developmental mechanism producing integration of the cranium as a whole, as well as integration of the neurocranium, varies throughout postnatal ontogeny. In contrast, we detected the ontogenetic stability of the mechanism responsible for covariation of viscerocranial traits which could provide ongoing flexibility of the viscerocranial covariance structure for high functional demands during lifetime. Findings from our study most likely support the idea of the 'palimpsest-like' model of covariance structure. Moreover, similarity or dissimilarity in the patterns of within and among individual variation in different sets of analyzed traits and comparisons across ontogenetic stages demonstrate how studies on small mammals other than mice can give new insights into postnatal cranial development. [ABSTRACT FROM AUTHOR]

The avian viscerocranium has been described by several investigators. It was perceived that a review on the ontogeny of the avian viscerocranium would be very useful to enrich the knowledge on this subject. The present article casts light on the avian viscerocranium starting from the early stages up to fairly late ones. [ABSTRACT FROM AUTHOR]

The skull is a complex structure that has frequently been studied for the patterns of morphological integration and modularity. The ventral side of the skull can be divided into two functional modules, the neurocranium composed of the braincase, eyes and ears, and the viscerocranium composed of the jaw apparatus. The aim of this study was to test the ventral cranium of the European ground squirrel Spermophilus citellus(Linnaeus, 1766) for this partitioning as sciurid skull is believed to be highly integrated without clear divisions into subunits. Additionally, I compared the degree of modularity between juveniles and adults. Hypothesized modularity was tested on 159 (43 juveniles and 116 adults)skulls by applying geometric morphometric method based on Escoufier RV coefficient. In adults, the results yielded strong support to the hypothesis that the viscerocranium and neurocranium are separate modules. In juveniles, two-module organization of the skull was also confirmed, but the hypothesized modules were much more integrated with each other. Although allometry can be a strong integrating factor, it had very little influence on the hypothesized modularity of the S. citellus skull. A permutation test for the difference in the degree of modularity between juveniles and adults was marginally significant. The change in the strength of integration between the viscerocranium and neurocranium in the S. citellus skull during ontogeny, with the higher level of modularity in adults than in juveniles, is probably a consequence of the transition from suckling to gnawing of food and greater specialisation of the two functional modules.

The study of inborn genetic errors can lend insight into mechanisms of normal human development and congenital malformations. Here, we present the first detailed comparison of cranial and neuro pathology in two exceedingly rare human individuals with cyclopia and alobar holoprosencephaly ( HPE) in the presence and absence of aberrant chromosome 18 ( aCh18). The aCh18 fetus contained one normal Ch18 and one with a pseudo-isodicentric duplication of chromosome 18q and partial deletion of 18p from 18p11.31 where the HPE gene, TGIF, resides, to the p terminus. In addition to synophthalmia, the aCh18 cyclopic malformations included a failure of induction of most of the telencephalon - closely approximating anencephaly, unchecked development of brain stem structures, near absence of the sphenoid bone and a malformed neurocranium and viscerocranium that constitute the median face. Although there was complete erasure of the olfactory and superior nasal structures, rudiments of nasal structures derived from the maxillary bone were evident, but with absent pharyngeal structures. The second non- aCh18 cyclopic fetus was initially classified as a true Cyclops, as it appeared to have a proboscis and one median eye with a single iris, but further analysis revealed two eye globes as expected for synophthalmic cyclopia. Furthermore, the proboscis was associated with the medial ethmoid ridge, consistent with an incomplete induction of these nasal structures, even as the nasal septum and paranasal sinuses were apparently developed. An important conclusion of this study is that it is the brain that predicts the overall configuration of the face, due to its influence on the development of surrounding skeletal structures. The present data using a combination of macroscopic, computed tomography (CT) and magnetic resonance imaging (MRI) techniques provide an unparalleled analysis on the extent of the effects of median defects, and insight into normal development and patterning of the brain, face and their skeletal support. [ABSTRACT FROM AUTHOR]

This study aimed at answering the question whether production of new colour variants of American mink in mink farms using mutations may entail changes in skull morphology and relationships between the bone elements building it. Analyses were made on the skulls of 56 eight-month-old males and females of two American mink colour variants (standard Brown and mutant Sapphire) from the same farm. Mean values, standard deviations and coefficients of variation were determined for carcass weight, cranial and mandibular weights and 7 dorsal surface, 8 lateral surface and 11 basal surface traits of the skull. The values of 24 cranial and mandibular indices and the values of sexual size dimorphism (SSD), i.e. a coefficient describing differences between sexes, were calculated. It was demonstrated that mutant colour variants of American mink may be a significant source of variation (P≤0.05 and P≤0.01) for some traits of skull morphology and relationships between respective bone elements of viscerocranium and neurocranium. [ABSTRACT FROM AUTHOR]

Traditionally, the cartilaginous viscerocranium of vertebrates is considered as neural crest (NC)-derived. Morphological work carried out on amphibian embryos in the first half of the XX century suggested potentially mesodermal origin for some hyobranchial elements. Since then, the embryonic sources of the hyobranchial apparatus in amphibians has not been investigated due to lack of an appropriate long-term labelling system. We performed homotopic transplantations of neural folds along with the majority of cells of the presumptive NC, and/or fragments of the head lateral plate mesoderm (LPM) from transgenic GFP+ into white embryos. In these experiments, the NC-derived GFP+ cells contributed to all hyobranchial elements, except for basibranchial 2, whereas the grafting of GFP+ head mesoderm led to a reverse labelling result. The grafting of only the most ventral part of the head LPM resulted in marking of the basibranchial 2 and the heart myocardium, implying their origin from a common mesodermal region. This is the first evidence of contribution of LPM of the head to cranial elements in any vertebrate. If compared to fish, birds, and mammals, in which all branchial skeletal elements are NC-derived, the axolotl (probably this is true for all amphibians) demonstrates an evolutionary deviation, in which the head LPM replaces NC cells in a hyobranchial element. This implies that cells of different embryonic origin may have the same developmental program, leading to the formation of identical (homologous) elements of the skeleton. [ABSTRACT FROM AUTHOR]

This study aimed at presenting the values of 47 metric traits and 20 cranial indices of the skull of 291 mature farm chinchillas and comparing these data with those being determined on 32 chinchilla skull specimens from the Natural History Museum in London. Measurements of the viscerocranium, neurocranium and mandible parameters were taken. No normal distribution of these traits was observed. The values of selected Spearman's rank correlation coefficients were calculated. It was found that most cranial traits of the farm chinchillas showed statistically significantly higher values (P≤0.01) when compared to those being determined on the skulls of museum specimens. The effect of the farm environment, in which the farm chinchillas had been kept for many generations, was a likely reason for these differences. [ABSTRACT FROM AUTHOR]

Abstract: The present article shows the following points: The quadrate and Meckel’s cartilages have separate centres of chondrification. A symphsis Meckelii is absent. Meckel’s cartilage has three processes. These are processus mandibularis externus, processus mandibularis internus and retroarticularis. The quadrate cartilage has five processes; orbitalis, medialis, lateralis, oticus and the ventral articular processes. The columella auris has two centres of chondrification, a medial otostapedial centre (the stapes) and a lateral hyostapedial centre. [Copyright &y& Elsevier]

At the level of the inferior viscerocranium, the strong mastication forces determine the constitution of three resistance structures : the superior mandibular arch, the inferior mandibular arch, the oblique mandibular arch. [ABSTRACT FROM AUTHOR]

Abstract: Barx1 modulates cellular adhesion molecule expression and participates in specification of tooth-types, but little is understood of its role in patterning the pharyngeal arches. We examined barx1 expression during zebrafish craniofacial development and performed a functional analysis using antisense morpholino oligonucleotides. Barx1 is expressed in the rhombencephalic neural crest, the pharyngeal arches, the pectoral fin buds and the gut in contrast to its paralogue barx2, which is most prominently expressed in the arch epithelium. Additionally, barx1 transient expression was observed in the posterior lateral line ganglia and developing trunk/tail. We show that Barx1 is necessary for proliferation of the arch osteochondrogenic progenitors, and that morphants exhibit diminished and dysmorphic arch cartilage elements due to reductions in chondrocyte differentiation and condensation. Attenuation of Barx1 results in lost arch expression of osteochondrogenic markers col2a1, runx2a and chondromodulin, as well as odontogenic marker dlx2b. Further, loss of barx1 positively influenced gdf5 and chordin, markers of jaw joint patterning. FGF signaling is required for maintaining barx1 expression, and that ectopic BMP4 induces expression of barx1 in the intermediate region of the second pharyngeal arch. Together, these results indicate an essential role for barx1 at early stages of chondrogenesis within the developing zebrafish viscerocranium. [Copyright &y& Elsevier]