Part Of Arch Research Articles

Arterial lesions in hypercholesterolaemic Yoshida rats: morphological evaluation.

The aortic wall structure of genetically determined hypercholesterolaemic (Yoshida) and control (Brown-Norway) rats was investigated by transmission and scanning electron and light microscopy. Leucocyte adherence mostly at branch sites and irregular protrusive structures were observed on the endothelial surface of the thoracic aorta of Yoshida, but not of Brown-Norway rats. The subendothelial space of the aortic wall of Yoshida rats was characterized by intimal cushions consisting of smooth muscle cells of 'synthetic phenotype' associated with adhering leucocytes and lipid droplets. Lipid infiltration of the cytoplasm of medial smooth muscle cells was observed on the inner part of the aortic arch and on the lateral parts of the large branches of Yoshida rats. This model of spontaneously hyperlipidaemic Yoshida rats is an appropriate 'moderate' injury system, which may be useful for studies of multiple risk factors for atherogenesis.

Experimental analysis of Msx‐1 and Msx‐2 gene expression during chick mandibular morphogenesis

Homeobox-containing genes are thought to be involved in regulating pattern formation in a variety of tissues during embryogenesis. We have examined the expression of the homeobox-related genes Msx-1 and Msx-2 during the development of the chick mandibular arch. Northern blot hybridization indicates that transcripts for both Msx-1 (1.6 Kb) and Msx-2 (3 Kb) are present in the mandibular arch as early as stage 18. The levels of both transcripts in the whole mandible decrease as cartilage is formed in vivo and in vitro. Using in situ hybridization, transcripts of Msx-1 were localized in high amounts to the mesenchyme of the mesial tips of the arches. Msx-2 transcripts were localized in high amounts to medial regions of the arches. Little or no hybridization of either probe was detected in the chondrogenic and myogenic regions of the arches. Transcripts of both genes were also excluded from calcified bone and cartilage. Our results further demonstrate that the mesial tip mesenchyme expressing Msx-1 includes areas of highly proliferative cells and has in vitro chondrogenic potential. The region of mesenchymal cells expressing the Msx-2 gene overlap with areas of developmentally programmed cell death which also contain very few proliferative cells and lack chondrogenic potential in vitro. These results are consistent with the possibility that Msx-1 may be involved in the outgrowth of the mandibular arch and Msx-2 may be involved in both developmentally programmed cell death and delineating the non-chondrogenic region of the medial part of the mandibular arch.

Soft tissue management in glenohumeral arthoplasty

The soft tissue envelope is the composite of anatomic parts that includes the deltoid muscle, part of the coracoacromial arch, the rotator cuff, the capsule, and the synovium. Successful management of these parts relative to their tension, balance, competence, and quality greatly affect the function and longevity of total shoulder replacement prosthetics. This article addresses the surgical techniques required to deal with the specific soft tissue envelope problems peculiar to different disease entities.

Radical resection of vertebral body tumours. A surgical technique used in ten cases

An operation for radical resection of a tumour of the vertebral body and part of the neural arch is described. The approach is posterior and from both sides of the spine. The posterior approach is used to remove the healthy part of the neural arch, mobilise the dura, divide involved nerve roots and carry out the posterolateral parts of the spinal osteotomies or disc divisions. On one side, usually the right, the sides of the vertebral body or bodies are freed and the osteotomies or disc divisions are extended. Then from the other side, a posterolateral thoracotomy or lumbotomy allows completion of the dissection with radical resection by rolling the specimen away from the dura. Ten operations are reported in which up to three and a half vertebrae were resected. Spinal reconstruction was by internal fixation and grafting preferably with vascularised bone. The results were satisfactory after follow-up for as long as eight years.

The management of a complex midfoot fracture with circular external fixation

Midfoot injuries are uncommon, accounting for only 0.5 per cent of all fracture dislocations (Wilson, 1933). The cuboid articulates with five other bones within the foot and is therefore an integral part of the lateral arch. This is a rigid structure, important in maintaining the anatomy and strength of the foot, and has a tendency to ‘snap’ under duress, producing comminuted fractures of the cuboid (Helal and Wilson, 1988). The navicular lies within the more mobile medial arch, disruption of which will lead to functional disability, as its role within the foot is one of propulsion A major study of midfoot fractures and dislocation was published in 1975 by Main and Jbwett. They designed a classification based upon mechanism of injury, with crushing trauma forming one of the smaller groups. Distinct mechanisms of injury are not described within this group, but in general, there is usually more than one fracture, and the injury is commonly open in nature. Medial arch injuries lead to degenerative changes in the long term, causing pain and stiffness on walking, and in Main and Jowett’s study, damage to the lateral arch resulted in nothing better than poor to fair outcomes. Recognized treatment involves open reduction and internal fixation followed by the use of a plaster, with or without weight bearing. Nevertheless the injury is notoriously difficult to bring to a satisfactory conclusion, due to collapse of the lateral arch. We present a new method which allows early mobilization by the patient whilst still maintaining good fracture reduction.

Miocene Carbonate Platforms in the Polish Carpathians (Central Paratethys). Foraminiferal record

The Neogene in Central Paratethys was the period when flysch deposition was replaced by that of molasse in both the Carpathian foldbelt and its foredeep. The sedimentation processes were coeval, closely relevant with tectonic phases of the Carpathian orogen evo¬ lution. The paper deals with Middle Miocene (Badenian) Lithothamnium-be&rmg sediments located in south-east Poland (Rzeszow vicinity), which were deposited in piggyback basins on the folded flysch unit They consist of organodetrital limestones inter-bedded by marly clays, and yield red algae, Foraminifera and many fossils of shallow-water fauna. The foraminiferal assemblages of Discorbacea, Rotaliacea and Orbitoidacea are dominating in the region. Cibicides lobatulus, numerous Amphistegina , Elphidium , Rosalina group, Discorbis, as well as frequent arenaceous and plank-tonic taxa, are present in these deposits. Differentiation of foraminifera palaeocoenosis have been oberved and interpreted as being due to palaeogeographic differences of each basin. Globigerinacea and Radiolaria taxa of the deposits were used as biostratigraphic indica¬ tors. Conclusion on tectonic position of the carbonate deposits could be supported by foraminiferal data. The resolution implays a thesis on Sarmatian orogenic activity at this part of Carpathian arch.

The Chukchi Sea Planning Area, Alaska: Structural Development, Basin Analysis and Hydrocarbon Potential

Seismic stratigraphic and seismic fault evidence both show that the Central Chukchi basin is a north-trending, fault-controlled basin, which developed at the beginning of early Mississippian time. About 20 km thickness of sediments have been deposited in the basin. Using a simple flexural model a series of 3-dimensional basement motion patterns with time was produced. From these characteristic patterns two stages of basement evolution can be recognized: the first is basement subsidence controlled by regional extensional fault systems during the period from early Mississippian to later Jurassic: the second stage is basement evolution as two nearly separate blocks from the beginning of Early Cretaceous. The west block development is related to reactivation of the old fault system, while the subsidence of the east block is caused by tectonism and associated sediment loading due to progressive thrusting northward of the Brooks Range. Quantitative basin modeling techniques show that many uncertainties occur when applying mathematical and computer models to simulate a sedimentary basin, especially in a frontier area where only limited data are available. In this study, quantitative basin modeling techniques applied to the Chukchi Sea Planning Area, Alaska, demonstrate how uncertainty can be handled. The Chukchi Sea Planning Area encompasses about 127,000 square kilometers of the northwestern Alaska continental shelf and lies offshore of the Natural Petroleum Reserve in Alaska. Only seismic data and a few remote onshore wells are available in the Planning Area. Compared with the North Slope of Alaska, the Planning Area has had a significantly different structural history. In addition, most of the strata in the Area are currently thermally mature to overmature and in the stage of generating dry gas. The prospective areas for oil are the margins of the central Chukchi Basin, such as the Chukchi platform, Herald Arch and northeast part of the basin.

Calcification of the aortic wall in hypercalcemic rabbits.

The mineralization process was investigated in the aortic wall of hypercalcemic rabbits. The elevated calcium level in serum was induced by intramuscular injection of vitamin D3. The animals were killed at different times of the experiment (max. 246 d). The freeze-dried tissue homogenates were used for elemental composition studies by means of proton induced X-ray emission (PIXE) and atomic absorption spectroscopy. The structural information was obtained from infrared (IR) and X-ray diffraction (XRD) spectra. Moreover, the ascending part of the aortic arch was separated and used for micro-PIXE (PIXE in combination with proton microprobe) and histochemical examinations. It was found that hypercalcemia (blood serum Ca content elevated by about 20%) induced calcification of the aortic wall. The mineral phase within the aortic wall consisted of Ca-P salts. The Ca/P ratio continuously increased during the experiment and approached 2 after 246 d of the vitamin D3 treatment. The IR and XRD studies made possible the identification of the complex phase composition of the samples. The hydroxyapatite crystals were detected after 196 days, however, in earlier phases of the experiment, amorphous calcium phosphate, dicalcium phosphate dihydrate and octacalcium phosphate were also observed. On the basis of the data obtained, the mechanism of the precipitation and growth of inorganic deposits in the tunica media of the aortic wall was discussed.

Relationship between tongue volume and lower dental arch sizes

The interrelation between the tongue volume and the lower dental arch sizes (arch width and area) was studied by the original methods that we developed. A plane perpendicular to the occlusal plane and 40 mm posterior to the lower incisal point was taken as the posterior border of the tongue and the arch. The tongue volume and the lower dental arch sizes were measured anterior to this border with plaster models. The correlations between the parameters obtained from 74 Japanese adults (37 men and 37 women) with normal occlusion were statistically analyzed. The results showed that (1) both the mean tongue volume and the mean lower dental arch sizes were significantly larger in men than in women; (2) the tongue volume and the lower dental arch sizes were significantly correlated; and (3) these correlations tended to be higher at the more posterior part of the dental arch.

Fatal rupture of an unsuspected post-traumatic aneurysm of the thoracic aorta during pregnancy.

A 27 year old woman presented during the third trimester of her second pregnancy complaining of chest pain. A chest radiograph showed a large aneurysm arising from the distal part of the aortic arch. She was transferred to the regional cardiothoracic centre but died suddenly on arrival. Necropsy confirmed a ruptured saccular aortic aneurysm arising just distal to the left subclavian artery. A history of a road traffic accident at the age of 12 was obtained from relatives after the patient's death. Vascular and haemodynamic changes in pregnancy may have caused the rupture of this previously silent post-traumatic aortic aneurysm.

Epithelio--mesenchymal interactions are critical for Quox 7 expression and membrane bone differentiation in the neural crest derived mandibular mesenchyme.

In higher vertebrates, branchial arch mesenchyme (ectomesenchyme) is derived from the cephalic neural crest. The ectomesenchyme of the mandibular arch yields the Meckel's cartilage and several membrane bones. We previously reported the isolation of a quail homeobox gene, Quox 7. In common with its mouse counterpart Hox 7, Quox 7 is highly expressed in the medioventral part of the mandibular arch and later in the precursor cells of the membrane bones. Since bone differentiation from ectomesenchyme is strictly dependent upon a signal provided by the mandibular epithelium, we decided to see whether the regulation of Quox 7 gene activity might be correlated with epithelio--mesenchymal interactions. Quox 7 expression was studied in E3 mandibular ectomesenchyme cultured in vitro or grafted on the chick chorioallantoic membrane either alone or recombined with the homotopic and heterotopic epithelia. We found that Quox 7 mRNA was undetectable after 48 h in cultures of mesenchyme alone while it remained abundant in non-cartilaginous tissue of the mandibular arch ectomesenchyme recombined with its own epithelium. The signal provided by the mandibular epithelium for Quox 7 expression can also arise from various heterotopic epithelia, e.g. of dorsal or ventral body wall and of limb bud. Thus the effect of the epithelium on Quox 7 expression in mesenchymal cells strictly parallels that on bone formation. These results strongly suggest that the epithelio-mesenchymal interactions have an essential role on the regulation of Quox 7 gene, the product of which seems to be, in turn, necessary for the execution of the skeletal developmental program in the facial area.

Teeth, tooth spaces, and prosthetic appliances in elderly men in Malmö, Sweden

A group of 483 men, all of whom were 68 or 69 yr old and had lived for a long time in the city of Malmö were examined with regard to number of teeth present, removable dentures, fixed bridges, and tooth spaces. 76.4% had one or more natural teeth remaining, 59.2% had removable dentures, and 0.2% were edentulous and without dentures. The mean number of teeth present in a fixed dentition calculated on dentate subjects was 16.21 +/- 8.02, including teeth replaced by pontics and 15.0 +/- 7.44 when natural teeth only were recorded. The number of bridges was high, 28.8% of natural dentate persons having bridgework. This cohort had fewer remaining teeth than in similar groups in other areas of Sweden, but more fixed bridges. 19.5% had open tooth spaces corresponding to one or more teeth in the visible parts of the dental arches. The availability of dentistry has been extremely good in Malmö and financial support for all types of dental care has been provided for all inhabitants since 1974. In spite of this, a low number of remaining teeth and many untreated tooth spaces in visible part of the dental arches were found, though on the other hand much fixed bridgework was found. It appears from the present study that the population tends to polarize into two groups, namely one group which takes advantage of the dental services and one which does not.

Palatoquadrate and its ossifications: Development and homology within osteichthyans.

The palatoquadrate and associated dermal bones have significant evolutionary transformations among teleostomes and provide numerous features that characterize teleostomian subgroups. The palatoquadrate forms the upper part of the mandibular arch and is present as a single cartilaginous element in the early ontogeny of teleostomes, except for some advanced teleosts such as siluroids where it is divided into pars autopalatina and pars pterygoquadrata. During ontogeny, the palatoquadrate may ossify as a unit, with a pars autopalatina (absent in Acanthodii), pars quadrata, and pars metapterygoidea in teleostomes (e.g., primitive acanthodians and actinopterygians, onychodonts, and rhipidistians). However, the palatoquadrate may remain cartilaginous (e.g., chondrosteans) or it may ossify as separate elements (e.g., autopalatine, metapterygoid, and quadrate) as occurs in advanced acanthodians, Polypterus and advanced actinopterygians, and advanced actinistians. From the single-unit pattern, separate autopalatine, metapterygoid, and quadrate evolve in parallel in the three teleostomian subgroups. Therefore, it is necessary to distinguish between actinopterygian and actinistian autopalatines and among acanthodian, actinopterygian, and actinistian metapterygoids and quadrates. A palatoquadrate fused with the neurocranium occurs in parallel in dipnoans. There are differences in the timing of ossification of the autopalatine, metapterygoid, and quadrate. The autopalatine ossifies late in ontogeny in Polypterus, Amia, and primitive teleosts (absent in lepisosteids and osteoglossmorphs), whereas both metapterygoid and quadrate ossify early in ontogeny. The early ossification of the autopalatine is characteristic of clupeocephalan teleosts. During ontogeny, tooth plates (not forming a separate dermometapterygoid) fuse with the metapterygoid in actinopterygians. Pars autopalatina, pars metapterygoidea, and pars quadrata are regions at the three corners of the single-unit palatoquadrate present in primitive teleostomes; there are no clear limits among these regions, but they may be identified by their processes, articular facets, and topographical relationships with surrounding bones and the orbit. Autopalatine, metapterygoid, and quadrate are chondral bones, perichondrally ossified. Dermal elements such as dermopalatine(s), entopterygoid, ectopterygoid, and tooth plates may cover the palatoquadrate medially. The predermopalatine that originates in front of pars autopalatina in Cladistia and the "dermopalatine" that lies medial to the ectopterygoid in Ginglymodi are specializations of these groups. A dermopalatine fused with the autopalatine is characteristic of clupeocephalan teleosts. Highly specialized tendon bone pterygoids are found in some teleosts (e.g., siluroids). The presence of both maxilla and lacrimal lateral to the pars autopalatina is synapomorphous of osteichthyans. The eye supported by the bony palatoquadrate is a teleostomian synapomorphy. Dermal elements support the eye in actinopterygians, the entopterygoid in advanced actinopterygians, but the ectopterygoid in lepisosteids. A quadratojugal is a synapomorphy of osteichthyans but exhibits a number of transformations in connection with the vertical pit-line and the preopercular canal; a quadratojugal bearing the vertical pit-line is the primitive condition for osteichthyans. Ontogenetic evidence does not support the homology of the membranous posterior process of the teleostean quadrate with the quadratojugal. The lack of a quadratojugal and the presence of the elongate posterior or posteroventral process of the quadrate is a synapomorphy of teleosts.

Digeorge anomaly in an infant with deletion of chromosome 22 and dup(9p) due to adjacent type II disjunction

A term white girl presented with low birth weight, minor anomalies, and congenital heart defects. The infant had microcephaly, upslanting palpebral fissures, prominent nasal bridge, short philtrum, thin upper lip vermilion, down-turned corners of the mouth, receding mandible, and short broad neck. The hands showed proximal placement of the thumbs, bilateral clinodactyly of the index finger, and bilateral transverse crease. Both hands were clenched, with the index finger overlapping the third finger and the fifth finger overlapping the fourth. There was also talipes calcaneo-valgus, bilateral dorsiflexion of the metatarsophalangeal joints, flexion of the interphalangeal joints, and hypoplasia of all nails. The patient's karyotype was 46,XX,-22, + der(9)t(9;22)(q21.13;q12.1)mat; the mother had the balanced translocation 46,XX,t(9;22)(9pter----9q21.13::22q12.1----22qter++ +;22pter---- 22q12.1::9q21.3----9qter). The infant died at age 10 days, and the autopsy showed absent thyroid isthmus and rudimentary thymus, with one small ectopic parathyroid attached to it. The lungs were hypoplastic, with abnormal lobation. The cardiac anomalies included truncus arteriosus, truncal valve stenosis, single carotid trunk, subclavian arteries arising from the distal part of the aortic arch, atrial and ventricular septal defects, right ventricular hypertrophy, and a hypoplastic left pulmonary artery. Also, multiple small accessory spleens were present in addition to a normal-sized spleen. This case combines features associated with DiGeorge anomaly and dup(9p). The chromosome abnormality in this patient appears to have arisen in a maternal germ cell due to adjacent type II disjunction.

A New Model of Particle Retention and Branchial Sieve Adjustment in Filter-Feeding Bream (Abramis brama, Cyprinidae)

A new model for filter feeding in bream (Abramis brama, Cyprinidae) is presented based on the three dimensional architecture of the branchial sieve. Transverse ridges on the upper surface of the gill arches form a system of channels in which food particles appear to be retained. These ridges are formed by a fleshy interconnection between the middle part of the gill arch and the bony parts of its gill rakers. Muscles attached to the rakers, present only on the lateral edge of the gill arch, indicate movability of the lateral bony raker element. If the fish is foraging on particles smaller than the channel diameter, movement of these gill rakers probably adjusts the sieve by reducing the channel diameter of the opposite channel. Selectivity of bream depends on available size classes of zooplanktons and changes in selectivity are attributed to adjustment of the branchial sieve. The channel model has been tested with feeding experiments and X-ray cinematography. The reconstructed paths of marked food particles show that particles follow the hypothesized path. Particle retention occurred mainly at the expected medial site of the arches. Our study strongly supports the channel model of particle retention.

Diapiric origin of the Blytheville and Pascola arches in the Reelfoot rift, east-central United States: Relation to New Madrid seismicity

Research Article| November 01, 1990 Diapiric origin of the Blytheville and Pascola arches in the Reelfoot rift, east-central United States: Relation to New Madrid seismicity F. A. McKeown; F. A. McKeown 1U.S. Geological Survey, Box 25046, MS 966, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar R. M. Hamilton; R. M. Hamilton 2U.S. Geological Survey, 922 National Center, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar S. F. Diehl; S. F. Diehl 1U.S. Geological Survey, Box 25046, MS 966, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar E. E. Glick E. E. Glick 1U.S. Geological Survey, Box 25046, MS 966, Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Geology (1990) 18 (11): 1158–1162. https://doi.org/10.1130/0091-7613(1990)018<1158:DOOTBA>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation F. A. McKeown, R. M. Hamilton, S. F. Diehl, E. E. Glick; Diapiric origin of the Blytheville and Pascola arches in the Reelfoot rift, east-central United States: Relation to New Madrid seismicity. Geology 1990;; 18 (11): 1158–1162. doi: https://doi.org/10.1130/0091-7613(1990)018<1158:DOOTBA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Most of the earthquakes in the New Madrid seismic zone correlate spatially with the Blytheville arch and part of the Pascola arch, which are interpreted to be the same structure. Both arches may have formed by diapirism along the axis of the Reeffoot rift. Seismic, geophys ical, and drill-hole data indicate that the rocks in the arches are highly deformed and fractured and have gross lithologic properties that make them weaker than rocks adjacent to the arches. The weaker rocks are inferred to fail seismically more readily than the stronger rocks adjacent to the arches. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The dimensions of everyday class-II cavity preparations for amalgam.

Six hundred and ten epoxy plastic models, made from impressions of permanent teeth in which class-II cavity preparations for amalgam restorations had been prepared by eight Scandinavian dentists, were examined. The outlines of the cavity preparations were relatively large, with mean buccolingual extensions occlusally of 50% of the intercuspal distance and proximally of 40% of the length of the circumference of the proximal surface. There was a gradual increase in the size of the cavities towards the distal part of the dental arch, measured both in millimeters and in relation to the anatomic structures. The amount of hard tissue being removed varied among the operators and was possibly influenced by the dentist's ability to handle the cutting instruments. The large cavity preparations may be the result of using procedures for cavity preparation which are not adjusted to the tremendous cutting potential of modern dental instruments to produce stereotyped 'ideally designed' cavities.

Congenital absence of the C1 vertebral arch

Congenital absence of part of the anterior arch of the atlas, a rare disorder, was observed in two patients. The defect in the C1 cervical vertebrae, caused by congenital nonfusion of the arch of C1, may be confused with a cervical spinal fracture on plain radiographs of the cervical spine. The diagnosis is established by characteristic radiological changes, especially in the CT scan and bone scan. Because congenital anomalles of the cervical spine may predispose to instability of the cervical spine and can be confused with traumatic lesions, thorough evaluation is warranted. Treatment should be based on signs of instability, if present.

Dental anthropological study on crown trait

The previous researches on racial differences in the crown trait and the dental arch morphology have often treated these two factors independently. The purpose of this study was to investigate, recognizing their racial differences, whether there are any association between them.The sample consisted of plaster casts of dentition obtained from 142 Japanese, 109 Cancasian and 121 inhabitants of the Andes in Peru. The casts were preserved at the Department of Orthodontics of Tokyo Medical and Dental University.The variations of 30 crown traits, categorized and quantitatively graded, were compared among three races using two methods. Chi-square test analyzed the frequency distribution of each crown trait. The other method analyzed the total variation of 30 crown traits in each sample by the computation of the parameter of similarity.On the other hand, an interracial comparison of the dental arch morphology was made by superimposing the occlusal outlines of all teeth, each of which had been numerically expressed by polar coordinates of 36 points plotted equi-angulary on the occlusal contour.The results were as follows:1. Trait frequencies of shovel-shape, interstitial tubercle, groove pattern of the Y type and Carabelli's cusp were significantly different among the races examined, and the shovel-shape appeared to be a hereditary characteristic.2. The dental arch morphology, especially in the anterior part, was different among the races.3. The crown trait, particulary the shovel-shape, was related to factors composing the anterior part of upper dental arch; namely, the arch length, arch width and winging of the central incisors.

The development and homology of the chelonian carpus and tarsus.

The long-standing controversies involving the number and homologies of the elements of the carpus and tarsus of turtles are reviewed from a developmental perspective. The analysis is based on a detailed description of the chondrogenesis of the carpus and tarsus in the species Chelydra serpentina and Chrysemys picta. The first stage described is the differentiation of a Y-shaped chondrogenetic condensation involving the humerus (femur)-radius/ ulna (tibia/fibula). This stage is followed by the early formation of a series of connected condensations off the distal end of the postaxial element (ulna or fibula). This linear array, which we refer to as the primary axis, comprises the ulnare-distal carpal 4-metacarpal 4 in the carpus and the fibulare-distal tarsal 4-metatarsal 4 in the tarsus. There are two precondensations that branch off the primary axis. The proximal one will soon form the intermedium while the distal one will generate a digital arch that will give rise sequentially to digits 3-2-1, in this order. Digit 5 is not part of the digital arch and forms as an independent condensation. We emphasize that chondrogenetic foci often form as "branches" off existing condensations. This well-defined pattern of connectivity is used to establish unambiguous homologies and allows comparisons with other vertebrates. We conclude that preaxial elements such as the radiale and tibiale are absent in the turtles examined and probably in all turtles. The observed proximal elements that form in the anterior region of the limb and that are often homologized as radiale or tibiale have clear connections to the postaxial elements. For this reason we argue that these elements should be homologized as centralia. Therefore, we find two chondrogenetic condensations in the tarsus and three in the carpus, which we consider centralia. They subsequently fuse with neighboring elements in a complex pattern. We also describe the variable presence of a late-developing element in the tarsus of Chelydra, which, to our knowledge, has never been described. We propose this element to be an atavistic pretarsale. Comparison of the chondrogenetic pattern in turtles with those described in the literature for other vertebrates indicates that there are two invariant patterns in all tetrapods with the exception of the urodeles. These are (1) the primary axis and (2) the digital arch.