Multiatlas segmentation as nonparametric regression

This paper proposes a novel theoretical framework to model and analyze the statistical characteristics of a wide range of segmentation methods that incorporate a database of label maps or atlases; such methods are termed as label fusion or multiatlas segmentation. We model these multiatlas segmentation problems as nonparametric regression problems in the high-dimensional space of image patches. We analyze the nonparametric estimator's convergence behavior that characterizes expected segmentation error as a function of the size of the multiatlas database. We show that this error has an analytic form involving several parameters that are fundamental to the specific segmentation problem (determined by the chosen anatomical structure, imaging modality, registration algorithm, and label-fusion algorithm). We describe how to estimate these parameters and show that several human anatomical structures exhibit the trends modeled analytically. We use these parameter estimates to optimize the regression estimator. We show that the expected error for large database sizes is well predicted by models learned on small databases. Thus, a few expert segmentations can help predict the database sizes required to keep the expected error below a specified tolerance level. Such cost-benefit analysis is crucial for deploying clinical multiatlas segmentation systems.

New developmental evidence clarifies the evolution of wrist bones in the dinosaur-bird transition

From early dinosaurs with as many as nine wrist bones, modern birds evolved to develop only four ossifications. Their identity is uncertain, with different labels used in palaeontology and developmental biology. We examined embryos of several species and studied chicken embryos in detail through a new technique allowing whole-mount immunofluorescence of the embryonic cartilaginous skeleton. Beyond previous controversy, we establish that the proximal-anterior ossification develops from a composite radiale+intermedium cartilage, consistent with fusion of radiale and intermedium observed in some theropod dinosaurs. Despite previous claims that the development of the distal-anterior ossification does not support the dinosaur-bird link, we found its embryonic precursor shows two distinct regions of both collagen type II and collagen type IX expression, resembling the composite semilunate bone of bird-like dinosaurs (distal carpal 1+distal carpal 2). The distal-posterior ossification develops from a cartilage referred to as "element x," but its position corresponds to distal carpal 3. The proximal-posterior ossification is perhaps most controversial: It is labelled as the ulnare in palaeontology, but we confirm the embryonic ulnare is lost during development. Re-examination of the fossil evidence reveals the ulnare was actually absent in bird-like dinosaurs. We confirm the proximal-posterior bone is a pisiform in terms of embryonic position and its development as a sesamoid associated to a tendon. However, the pisiform is absent in bird-like dinosaurs, which are known from several articulated specimens. The combined data provide compelling evidence of a remarkable evolutionary reversal: A large, ossified pisiform re-evolved in the lineage leading to birds, after a period in which it was either absent, nonossified, or very small, consistently escaping fossil preservation. The bird wrist provides a modern example of how developmental and paleontological data illuminate each other. Based on all available data, we introduce a new nomenclature for bird wrist ossifications.

Treatment of patellofemoral cartilage defects in the knee by autologous matrix-induced chondrogenesis (AMIC

This study presents the prospective two-year clinical and MRI outcome of autologous matrix-induced chondrogenesis (AMIC) for the treatment of patellofemoral cartilage defects in the knee. Ten patients were clinically prospectively evaluated during 2 years. MRI data were analysed based on the original and modified MOCART (Magnetic Resonance Observation of Cartilage Repair Tissue) scoring system. A satisfying clinical improvement became apparent during the 24 months of follow-up. The MOCART scoring system revealed a slight tendency to deterioration on MRI between one and 2 years of follow-up. However, the difference was not statistical significant. All cases showed subchondral lamina changes. The formation of intralesional osteophytes was observed in 3 of the 10 patients (30%). In conclusion, AMIC is safe and feasible for the treatment of symptomatic patellofemoral cartilage defects and resulted in a clinical improvement. However, the favourable clinical outcome of the AMIC technique was not confirmed by the MRI findings.

[Clinical anatomic study of Pitanguy ligament of the nose]

OBJECTIVE

To observe the origins and insertions of Pitanguy ligament,in order to find the anatomically theoretical basis for the treatment of nasal deformity such as drooping nose, short columella, gingival show.

METHODS

15 cadaveric heads fixed by 10% formalin were used. 12 specimens underwent nasal anatomic study. The skin was incised, along the nasal midline to expose the Pitanguy ligament. The origin of Pitanguy ligament and its relationship with surrounding tissue were studied. Then the Pitanguy ligament was taken out for HE staining. Longitudinal section along the ligament was observed. 3 specimens underwent harvesting of full-thickness nasal tissue from skin to periosteal membrane. Then the samples were used for HE staining to show histologic study of ligament at horizontal section.

RESULTS

Pitanguy ligament originates in the midline of lower third of the nasal superficial musculoaponeurotic system, extends down to the tip along the midline of the nasal dorsum and then turns backwards at the nasal tip, and runs between the medial crura of the lower lateral cartilages, inserts into the base of columella. Its muscle is connected with the orbicularis oris muscle and the depressor septi nasi muscle. HE staining showed the ligament consists of fibrous connective tissue, muscle tissue and other ingredients, but without cartilage.

CONCLUSIONS

Pitanguy ligament exists with complex histological composition, so its name is still controversial. Because it has multiple connection with the orbicularis oris muscle and the depressor septi nasi muscle, so cutting or shortened the Pitanguy ligament can treat deformity of nose and lip by adjustment of nasolabial angles and the nasal length.

Keyhole chemical exchange saturation transfer

The keyhole technique, which involves the acquisition of dynamic data at low resolution in combination with a high-resolution reference, is developed for the purposes of chemical exchange saturation transfer (CEST) imaging, i.e., Keyhole CEST. Low-resolution data are acquired with saturation applied at different frequencies for Z-spectra, along with a high-resolution reference image taken without saturation. Three methods for high-resolution reconstruction of Keyhole CEST are evaluated using the values from quantitative high-resolution CEST maps. In addition, Keyhole CEST is applied for collection of data used for B(0) correction. The keyhole approach is evaluated for CEST contrast generation using exchanging protons in hydroxyl groups. First, the techniques are evaluated in vitro using samples of dextrose and chondroitin sulfate. Next, the work is extended in vivo to explore its applicability for gagCEST. Comparable quantitative gagCEST values are found using Keyhole CEST, provided the structure or region of interest is not limited by the low-resolution dataset.

[Early bone and cartilage histogenesis in embryonic Japanese quails in the conditions of microgravity]

The article presents the results of a comparative histological investigation of skeletal bones genesis in Japanese quail embryos developed in the spaceflight microgravity (space group) and laboratory (control group). Total preparations of 4-day-old embryos from both groups demonstrated clearly that the cartilaginous anlage of the femoral bone had central, dyaphisial, 2 epiphysial and 2 proliferation zones. By day 7 of embryogenesis, cartilaginous anlages had grown in size in both groups due to intensive chondrocytes multiplication and gain in the intercellular substance mass. Tibial cuff in space embryos measured half and femoral cuff was 2.3 times smaller in comparison with these parameters in the control group. In addition, intensity of chondrocyte multiplication was reduced Histological profiles of the femur and tibia in 10-day old embryos of the control pointed to enhancement of osteogenesis. The metaphysis zone contained distinct mitosis figures on different stages of division. Bone deposition could be seen below the peristoma. The osteogenesis cuff spread up to the femoral anlage metaphysis; cartilage was calcined. Space embryos display retard osteogenesis. There were ingrown blood vessels in the region of cartilage destruction; however, vessels grown in the periosteum were less in number as compared with the laboratory control. Also, the perichondral ossification layer was considerably thinner, whereas the osseous cuff was 1.3 and 1.45 times shorter in the femur and tibia, respectively. To sum up, the histological investigation of bones from 4-, 7- and 10- day old Japanese quail embryos demonstrated retardation of osteogenesis in the conditions of microgravity.

Multiple roles and interactions of Tbx4 and Tbx5 in development of the respiratory system

Normal development of the respiratory system is essential for survival and is regulated by multiple genes and signaling pathways. Both Tbx4 and Tbx5 are expressed throughout the mesenchyme of the developing lung and trachea; and, although multiple genes are known to be required in the epithelium, only Fgfs have been well studied in the mesenchyme. In this study, we investigated the roles of Tbx4 and Tbx5 in lung and trachea development using conditional mutant alleles and two different Cre recombinase transgenic lines. Loss of Tbx5 leads to a unilateral loss of lung bud specification and absence of tracheal specification in organ culture. Mutants deficient in Tbx4 and Tbx5 show severely reduced lung branching at mid-gestation. Concordant with this defect, the expression of mesenchymal markers Wnt2 and Fgf10, as well as Fgf10 target genes Bmp4 and Spry2, in the epithelium is downregulated. Lung branching undergoes arrest ex vivo when Tbx4 and Tbx5 are both completely lacking. Lung-specific Tbx4 heterozygous;Tbx5 conditional null mice die soon after birth due to respiratory distress. These pups have small lungs and show severe disruptions in tracheal/bronchial cartilage rings. Sox9, a master regulator of cartilage formation, is expressed in the trachea; but mesenchymal cells fail to condense and consequently do not develop cartilage normally at birth. Tbx4;Tbx5 double heterozygous mutants show decreased lung branching and fewer tracheal cartilage rings, suggesting a genetic interaction. Finally, we show that Tbx4 and Tbx5 interact with Fgf10 during the process of lung growth and branching but not during tracheal/bronchial cartilage development.

First evidence of dinosaurian secondary cartilage in the post-hatching skull of Hypacrosaurus stebingeri (Dinosauria, Ornithischia)

Bone and calcified cartilage can be fossilized and preserved for hundreds of millions of years. While primary cartilage is fairly well studied in extant and fossilized organisms, nothing is known about secondary cartilage in fossils. In extant birds, secondary cartilage arises after bone formation during embryonic life at articulations, sutures and muscular attachments in order to accommodate mechanical stress. Considering the phylogenetic inclusion of birds within the Dinosauria, we hypothesized a dinosaurian origin for this "avian" tissue. Therefore, histological thin sectioning was used to investigate secondary chondrogenesis in disarticulated craniofacial elements of several post-hatching specimens of the non-avian dinosaur Hypacrosaurus stebingeri (Ornithischia, Lambeosaurinae). Secondary cartilage was found on three membrane bones directly involved with masticatory function: (1) as nodules on the dorso-caudal face of a surangular; and (2) on the bucco-caudal face of a maxilla; and (3) between teeth as islets in the alveolar processes of a dentary. Secondary chondrogenesis at these sites is consistent with the locations of secondary cartilage in extant birds and with the induction of the cartilage by different mechanical factors - stress generated by the articulation of the quadrate, stress of a ligamentous or muscular insertion, and stress of tooth formation. Thus, our study reveals the first evidence of "avian" secondary cartilage in a non-avian dinosaur. It pushes the origin of this "avian" tissue deep into dinosaurian ancestry, suggesting the creation of the more appropriate term "dinosaurian" secondary cartilage.

Ontogeny of the alligator cartilago transiliens and its significance for sauropsid jaw muscle evolution

The cartilago transiliens is a fibrocartilaginous structure within the jaw muscles of crocodylians. The cartilago transiliens slides between the pterygoid buttress and coronoid region of the lower jaw and connects two muscles historically identified as m. pseudotemporalis superficialis and m. intramandibularis. However, the position of cartilago transiliens, and its anatomical similarities to tendon organs suggest the structure may be a sesamoid linking a single muscle. Incompressible sesamoids often form inside tendons that wrap around bone. However, such structures rarely ossify in reptiles and have thus far received scant attention. We tested the hypothesis that the cartilago transiliens is a sesamoid developed within in one muscle by investigating its structure in an ontogenetic series of Alligator mississippiensis using dissection, 3D imaging, and polarizing and standard light microscopy. In all animals studied, the cartilago transiliens receives collagen fibers and tendon insertions from its two main muscular attachments. However, whereas collagen fibers were continuous within the cartilaginous nodule of younger animals, such continuity decreased in older animals, where the fibrocartilaginous core grew to displace the fibrous region. Whereas several neighboring muscles attached to the fibrous capsule in older individuals, only two muscles had significant contributions to the structure in young animals. Our results indicate that the cartilago transiliens is likely a sesamoid formed within a single muscle (i.e., m. pseudotemporalis superficialis) as it wraps around the pterygoid buttress. This tendon organ is ubiquitous among fossil crocodyliforms indicating it is a relatively ancient, conserved structure associated with the development of the large pterygoid flanges in this clade. Finally, these findings indicate that similar tendon organs exist among potentially homologous muscle groups in birds and turtles, thus impacting inferences of jaw muscle homology and evolution in sauropsids in general.

Early ontogeny of the Atlantic halibut Hippoglossus hippoglossus head

An ontogenetic sequence of Atlantic halibut Hippoglossus hippoglossus larvae, reared in intensive culture conditions, was cleared and stained and histologically processed to determine normal cranial chondrification for specimens ranging from 0 to 41 days post-hatch (dph). Twenty-six cranial cartilaginous structures were described, at daily intervals post-hatch. The ontogenetic trajectory, composed of alternating steps and thresholds, was interpreted as saltatory. In comparison with other flatfishes, H. hippoglossus exhibits delayed onset of chondrification. From 9 dph onwards, the ontogenetic trajectory resembles more than that of the turbot Psetta maxima than that of the common sole Solea solea or the summer flounder Paralichthys dentatus and winter flounder Pseudopleuronectes americanus. Hippoglossus hippoglossus with the gaping-jaw malformation, common in intensively cultured individuals of this species, were examined histologically. The reason larvae cannot close their mouth, as their yolk-sac resorbs, seems to be related to the fusion of the interhyal to the hyosymplectic and ceratohyal with which it is normally articulated.

Morphology, distribution, mineral density and volume fraction of human calcified costal cartilage

This study examines the properties of calcifying human costal cartilage and adjacent rib bone using qualitative and quantitative micro-computed tomography analysis. Calcifications are categorized with respect to location, microstructure, shape, and contiguity using a novel classification scheme and quantified in terms of mineral density, volume fraction, and length of infiltration from the costo-chondral junction (CCJ). Calcifications were present throughout the cartilage by location and ranged from small diffuse calcifications to nodes, rods, plates, and even large complex structures that exhibited a microstructural morphology similar to a cross-section of diaphysial bone, with a dense shell surrounding a trabecular core. Solid microstructure was most common for calcifications (44.5%), and the morphologies were found to vary with location, with rods and plates being most prevalent at the periphery (91.7% of all rods, 98.4% of all plates). The average mineral density of the calcifications over all locations and morphologies was 658.8±86.36, compared with 662.7±50.37 mgHA cm(-3) for the adjacent rib bone. The calcification volume fraction (6.54±4.71%) was less than the volume fraction of rib bone (21.62±6.44%). The length of contiguous calcification infiltrating from the CCJ into the costal cartilage, when present, was 19.21±11.65 mm. These changes in the costal cartilage should be considered in biomechanical models of the thorax since the presence, location, and morphology of the calcifications alter the material behavior of the costal cartilage, as well as the structural behavior of the entire rib.

A role for FoxN3 in the development of cranial cartilages and muscles in Xenopus laevis (Amphibia: Anura: Pipidae) with special emphasis on the novel rostral cartilages

The origin of morphological novelties is a controversial topic in evolutionary developmental biology. The heads of anuran larvae have several unique structures, including the supra- and infrarostral cartilages, the specialised structure of the gill basket (used for filtration), and novel cranial muscle arrangements. FoxN3, a member of the forkhead/winged helix family of transcription factors, has been implicated as important for normal craniofacial development in the pipid anuran Xenopus laevis. We have investigated the effects of functional knockdown of FoxN3 (using antisense oligonucleotide morpholino) on the development of the larval head skeleton and the associated cranial muscles in X. laevis. Our data complement earlier studies and provide a more complete account of the requirement of FoxN3 in chondrocranium development. In addition, we analyse the effects of FoxN3 knockdown on cranial muscle development. We show that FoxN3 knockdown primarily affects the novel skeletal structures unique to anuran larvae, i.e. the rostralia or the fine structure of the gill apparatus. The articulation between the infrarostral and Meckel's cartilage is malformed and the filigreed processes of the gill basket do not develop. Because these features do not develop after FoxN3 knockdown, the head morphology resembles that in the less specialised larvae of salamanders. Furthermore, the development of all cartilages derived from the neural crest is delayed and cranial muscle fibre development incomplete. The cartilage precursors initially condense in their proper position but later differentiate incompletely; several visceral arch muscles start to differentiate at their origin but fail to extend toward their insertion. Our findings indicate that FoxN3 is essential for the development of novel cartilages such as the infrarostral and other cranial tissues derived from the neural crest and, indirectly, also for muscle morphogenesis.

Cartilage biology, pathology, and repair

Osteoarthritis is one of the most common forms of musculoskeletal disease and the most prominent type of arthritis encountered in all countries. Although great efforts have been made to investigate cartilage biology and osteoarthritis pathology, the treatment has lagged behind that of other arthritides, as there is a lack of effective disease-modifying therapies. Numerous approaches for dealing with cartilage degradation have been tried, but enjoyed very little success to develop approved OA treatments with not only symptomatic improvement but also structure-modifying effect. In this review we discuss the most recent findings regarding the regulation of cartilage biology and pathology and highlight their potential therapeutic values.

Photophysical mechanisms of collagen modification by 80 MHz femtosecond laser

Photophysical mechanisms of collagen photomodification (CFP) by the use of a 80 MHz, 780 nm femtosecond titanium-sapphire laser were investigated. Our observation that the decrease in collagen second harmonic generation and increase in two-photon autofluorescence intensity occurred primarily at sites where photoproducts were present suggested that the photoproducts may act to facilitate the CFP process. Laser power study of CFP indicated that the efficiency of the process depended on the sixth power of the laser intensity. Furthermore, it was demonstrated that CFP can be used for bending and cutting of collagen fibers and creating 3D patterns within collagen matrix with high precision (~2 μm).

Sodium inversion recovery MRI of the knee joint in vivo at 7T

The loss of proteoglycans (PG) in the articular cartilage is an early signature of osteoarthritis (OA). The ensuing changes in the fixed charge density in the cartilage can be directly linked to sodium concentration via charge balance. Sodium ions in the knee joint appear in two pools: in the synovial fluids or joint effusion where the ions are in free motion and bound within the cartilage tissue where the Na(+) ions have a restricted motion. The ions in these two compartments have therefore different T₁ and T₂ relaxation times. The purpose of this study is to demonstrate the feasibility of a fluid-suppressed 3D ultrashort TE radial sodium sequence by implementing an inversion recovery (IR) preparation of the magnetization at 7T. This method could allow a more accurate and more sensitive quantification of loss of PG in patients with OA. It is shown that adiabatic pulses offer significantly improved performance in terms of robustness to B₁ and B₀ inhomogeneities when compared to the hard pulse sequence. Power deposition considerations further pose a limit to the RF inversion power, and we demonstrate in simulations and experiments how a practical compromise can be struck between clean suppression of fluid signals and power deposition levels. Two IR sequences with different types of inversion pulses (a rectangular pulse and an adiabatic pulse) were tested on a liquid phantom, ex vivo on a human knee cadaver and then in vivo on five healthy volunteers, with a (Nyquist) resolution of ∼3.6 mm and a signal-to-noise ratio of ∼30 in cartilage without IR and ∼20 with IR. Due to specific absorption rate limitations, the total acquisition time was ∼17 min for the 3D radial sequence without inversion or with the rectangular IR, and 24:30 min for the adiabatic IR sequence. It is shown that the adiabatic IR sequence generates a more uniform fluid suppression over the whole sample than the rectangular IR sequence.

Reconstruction of large nasal septal perforations with a three layer galeal pericranial flap: an anatomical and technical study

OBJECTIVES

In this study, a modified surgical method was carried out to repair large nasal septal perforations with a galeal pericranial flap using endoscopic technique.

MATERIALS AND METHODS

Six adult human cadavers were dissected by applying the classic open rhinoplasty technique. Large perforations were created in the septal cartilages. To repair the perforations, we prepared galeal pericranial flaps with supraorbital neurovascular pedicles and calvarial bone grafts under endoscopic visualization. The flaps were inserted between the upper lateral cartilages and folded into three layers. The flaps were sutured to the nasal mucosa with absorbable sutures. The length, the width, the size of the flaps and the perforations were measured using an electronic caliper and a flexible ruler.

RESULTS

The mean length and width of the flap pedicles were measured as 26.8±5.1 mm (range 20 to 32 mm) and 19.3±2.6 mm (range 15 to 23 mm), respectively. In addition, the mean length and the width of the flaps were 54.1±4.9 mm (range 50 to 60 mm) and 51.6±7.8 mm (range 45 to 63 mm), respectively. All of the nasal septal perforations were repaired with a galeal pericranial flap.

CONCLUSION

The galeal-pericranial flap is well-vascularized and similar to the nasal mucosa for tissue thickness. Therefore, reconstruction with galeal-pericranial flaps can be an alternative surgical technique for repair of large nasal septal perforations.

Anatomical characteristics of the conchal cartilage with suggested clinical applications in rhinoplasty surgery

BACKGROUND

Numerous cartilage grafts from a number of donor sites have been described, each with a different shape and size. These donor sites include the nasal septum, costal chondral cartilage, and the conchal bowl. Although harvests from the conchal bowl are commonly-employed, the techniques have been minimally-described in the literature, particularly as it applies to rhinoplasty.

OBJECTIVES

The authors identify differences in the conchal bowl cartilage parameters that could aid in the planning and harvesting of conchal grafts during augmentation rhinoplasty.

METHODS

The authors dissected ears from fourteen cadavers (eight females and six males), ranging between 59 and 77 years of age. The conchal bowls were isolated, after which a reference point or was marked at the junction of the helical root and the conchal extension of the helical root. A cartilage grid was mapped out at 3-mm interval divisions with a horizontal limb axis parallel to the helical root extension and a vertical limb axis perpendicular to the latter. Conchal cartilage width, height, and thickness were then measured. Axial tissue slices were harvested and histologic preparations completed with hemotoxylin and eosin (H&E) staining to delineate microscopic characteristics of the cartilage.

RESULTS

Maximum conchal bowl width ranged from 1.9 to 2.9 cm and was widest on average over the cymba (2.4 ± 0.3 cm). Maximum conchal bowl height ranged from 1.7 to 3.1 cm and was greatest on average over the region posterior to the junction of the helical root and conchal bowl (2.4 ± 0.5 cm). Conchal bowl thickness ranged from 1.9 to 4.4 mm and was observed thickest over both the conchal extension of the helical root (3.5 ± 0.4 mm) as well as over a distinct region in the inferior-anterior aspect of the cavum (3.7 ± 0.9 mm). No difference in thickness was observed between the conchal extension of the helical root (3.5 ± 0.4 mm) and the distinct region in the inferioranterior aspect of the cavum (3.7 ± 0.9 mm; P > .05). Naturally-occurring cartilaginous divisions were appreciated on histologic specimens located at the junction of the cavum and external auditory meatus and at the junction of the helical root and conchal extension of the helical root.

CONCLUSIONS

The results, examination, and outline of conchal bowl parameters from cadaver cartilage demonstrated in this article will aid the surgeon in effectively obtaining the appropriate cartilage grafts for placement during rhinoplasty.

Primary rhinoplasty

Rhinoplasty is generally considered to be one of the most challenging, complex, and exciting of all the plastic surgery procedures. In this article, the authors discuss key concepts related to patient evaluation and analysis, as well as techniques and maneuvers that reliably lead to favorable long-term results in rhinoplasty.

Applied anatomy of the nasal lower lateral cartilage: a new finding

BACKGROUND

In most references to the nasal anatomy, the shape of the lower lateral cartilage (LLC) is described as a two-dimensional structure. However, the authors have found different forms of LLC in at least 40% of their open rhinoplasty cases during the past 20 years. This cartilage was found to have a three-dimensional hemispheric appearance and to be connected to the upper lateral cartilage (ULC) at the scroll area by an inward limb of this hemisphere. This inward limb may have an important role in producing asymmetry and flare of the nostril.

METHODS

The LLC of 286 patients was evaluated during open rhinoplasty over a 2-year period, with a focus mainly on the shape of this structure, especially at the LLC-ULC junction (scroll area).

RESULTS

A dome-shaped appearance of the LLC was noted in 40.9% of cases, and 11.5% of cases had bilateral LLC variation. This different anatomic form was seen mostly in patients with a strong bulbous nasal tip, although it was observed less frequently also in patients with narrow nasal tips.

CONCLUSION

At least one-third of the LLCs analyzed had a medial wall in addition to the lateral wall, which significantly increased the flare and recoil force of this structure. This makes this cartilage more redundant to reshaping procedures (straightening). Thus, special attention must sometimes be paid to this common anatomic variation to produce symmetric nostrils and to obtain a more aesthetically acceptable alar tip.

Functional anatomy of the Eustachian tube

The Eustachian tube (ET) is divided in 3 portions: a bony portion, a cartilaginous portion, and a junctional portion. From an anatomical-functional point of view, the bony portion of ET is the region of ventilation and clearance of secretions, and is lined by pseudostratified, ciliated, columnar epithelium, with an anti-gravitational direction of the drainage. The ET in the bony portion is in a state of forced opening. The cartilaginous portion is instead the heart of this dynamic system tube, because the mechanism of opening and closing of the tube is at this level. ET is normally closed, and it opens only during swallowing, being essential for good functioning of the middle ear, because it provides ventilation from the nasopharynx to the middle ear, and, at the same time, clearance of secretions from the middle ear-mastoid unit to the nasopharynx. Moreover, the ET protects the middle ear against nasopharyngeal pressure variations, ascending secretions, and microorganisms. The ability to develop all these functions makes the tube a complex organ.

Gill-filament ossifications: a possible morphological synapomorphy uniting the families Balitoridae and Cobitidae (Ostariophysi: Cypriniformes)

Ossifications associated with the gill filaments of members of the Balitoridae and Cobitidae are described for the first time. Although gill-filament ossifications are common in teleosts, similar ossifications were not observed in other members of the order Cypriniformes. Their presence is interpreted as a shared and derived character uniting the families Balitoridae and Cobitidae as a monophyletic group.

Development of the pharyngeal arch skeleton in Catostomus commersonii (Teleostei: Cypriniformes)

Skeletal elements of the gill arches of adult cypriniform fishes vary widely in number, size, and shape and are important characters in morphologically based phylogenetic studies. Understanding the developmental basis for this variation is thus phylogenetically significant but also important in relation to the many developmental genetic and molecularly based studies of the early developing and hence experimentally tractable gill arches in the zebrafish, a cyprinid cypriniform. We describe the sequence of the chondrification and ossification of the pharyngeal arches and associated dermal bones from Catostomus commersonii (Catostomidae, Cypriniformes) and make selected comparisons to other similarly described pharyngeal arches. We noted shared spatial trends in arch development including the formation of ventral cartilages before dorsal and anterior cartilages before posterior. Qualitatively variable gill arch elements in Cypriniformes including pharyngobranchial 1, pharyngobranchial 4, and the sublingual are the last such elements to chondrify in C. commersonii. We show that the sublingual bone in C. commersonii has two cartilaginous precursors that fuse and ossify to form the single bone in adults. This indicates homology of the sublingual in catostomids to the two sublingual bones in the adults of cobitids and balitorids. Intriguing patterns of fusion and segmentation of the cartilages in the pharyngeal arches were discovered. These include the individuation of the basihyal and anterior copula through segmentation of a single cartilage rod, fusion of cartilaginous basibranchials 4 and 5, and fusion of hypobranchial 4 with ceratobranchial 4. Such "fluidity" in cartilage patterning may be widespread in fishes and requires further comparative developmental studies.

The genesis of cartilage size and shape during development and evolution

How do cartilaginous elements attain their characteristic size and shape? Two intimately coupled processes underlie the patterned growth of cartilage. The first is histogenesis, which entails the production of cartilage as a discrete tissue; the second is morphogenesis, which pertains to the origins of three-dimensional form. Histogenesis relies on cues that promote the chondrogenic differentiation of mesenchymal cells, whereas morphogenesis requires information that imbues cartilage with stage-specific (e.g. embryonic versus adult), region-specific (e.g. cranial versus appendicular) and species-specific size and shape. Previous experiments indicate that early programmatic events and subsequent signaling interactions enable chondrogenic mesenchyme to undergo histogenesis and morphogenesis, but precise molecular and cellular mechanisms that generate cartilage size and shape remain unclear. In the face and jaws, neural crest-derived mesenchyme clearly plays an important role, given that this embryonic population serves as the source of chondrocytes and of species-specific patterning information. To elucidate mechanisms through which neural crest-derived mesenchyme affects cartilage size and shape, we made chimeras using quail and duck embryos, which differ markedly in their craniofacial anatomy and rates of maturation. Transplanting neural crest cells from quail to duck demonstrates that mesenchyme imparts both stage-specific and species-specific size and shape to cartilage by controlling the timing of preceding and requisite molecular and histogenic events. In particular, we find that mesenchyme regulates FGF signaling and the expression of downstream effectors such as sox9 and col2a1. The capacity of neural crest-derived mesenchyme to orchestrate spatiotemporal programs for chondrogenesis autonomously, and to implement cartilage size and shape across embryonic stages and between species simultaneously, provides a novel mechanism linking ontogeny and phylogeny.