The structure and function of the dermal pectoral girdle in bony fishes with particular reference to ostariophysines

The structure of the dermal pectoral girdle of teleostean fishes is analyzed in relation to its functions. In bony fishes the vertebral column, with a horizontal axis, and the pectoral girdle, with a basically vertical axis, form the only skeletal links between the head and the body. The individual bones of the dermal girdle are considered as supporting units joined by a series of articulations that permit differential movement between adjacent bones. The movements mediated by this linkage system are: lateral swinging of the head relative to the body, expansion of the distance between the central areas of the two pectoral girdles to permit passage of large food items, and fore-and-aft movements of the anteroventral ends of the cleithra relative to the skull. Among other factors affecting the structure of the dermal pectoral girdle are the provision for the support of the pectoral fin base and the requirement for the effective operation of a sleeve valve between the girdle and the opercular cover.
Modifications of the dermal pectoral girdle in ostariophysine fishes are discussed. A brief history of the bony fish girdle in terms of its functional components is postulated.     

The pectoral anatomy of selected Ostariophysi. II. The Cypriniformes and siluriformes

The pectoral myology and osteology of the cyprinoids Notemigonus crysoleucas, the golden shiner, and Catostomus commersonnii, the common white sucker, resemble those of generalized, lower teleosts in structure and function, except in features related to the manipulation of the massive fifth ceratobranchial of cyprinoids by muscles attaching on the girdle. Catostomus is more specialized in having unique intercostal muscles to the girdle, complex subclavian arteries and lack of a superficial trapezius muscle. The bony pectoral anatomy of the siluriform, Ictalurus nebulosus, the brown bullhead, is highly specialized in relation to the presence and locking of the massive pectoral spine which is formed of fused dorsal and ventral propterygial rays; there is consolidation of the girdle through fusion of bones, presence of unique stabilizing bony structures, firm symphyseal union of bilateral girdles and the presence of friction-surfaces of girdle and spine for locking. The movements of the spine are specialized in the greater guidance offered by the girdle. Myological specializations are related mainly to ventral appendicular muscles which lock the spine. The nervous and arterial systems are generalized.     

中国鲽形目鱼类骨骼的研究Ⅰ.肩带骨及腰带骨

本文比较了中国12属14种鲽形目鱼类的肩带骨及腰带骨,并参考了Ochiai(1963)有关日本钩嘴鳎等5属5种的研究;得知这些骨骼,特别是原始肩带骨与腰带骨,有退化趋势。这似因这些鱼类在向以体一侧侧卧,类似蝶泳姿势强化,偶鳍的功能逐渐变弱或消失,故支持偶鳍运动的这些骨骼也渐退化或消失。     

Growth of the pectoral girdle of the Leopard frog, Rana pipiens (Anura: Ranidae)

This article describes the growth of the anuran pectoral girdle of Rana pipiens and compares skeletal development of the shoulder to that of long bones. The pectoral girdle chondrifies as two halves, each adjacent to a developing humerus. In each, the scapula and coracoid form as single foci of condensed chondrocytes that fuse, creating a cartilaginous glenoid bridge articulating with the humerus. Based on histological sections, both the dermal clavicle and cleithrum begin to ossify at approximately the same time as the periosteum forms around the endochondral bones. The dermal and endochondral bones of the girdle form immobile joints with neighboring girdle elements; however, the cellular organization and growth pattern of the scapula and coracoid closely resemble those of a long bone. Similar to a long bone epiphysis, distal margins of both endochondral elements have zones of hyaline, stratified, and hypertrophic cartilages. As a result, fused elements of the girdle can grow without altering the glenoid articulation with the humerus. Comparisons of anuran long bone and pectoral girdle growth suggest that different bones can have similar histology and development regardless of adult morphology.     

Anatomy and early development of the pectoral girdle,fin, and fin spine of sturgeons (Actinopterygii: Acipenseridae)

Acipenseriformes hold an important place in the evolutionary history of bony fishes. Given their phylogenetic position as extant basal Actinopterygii, it is generally held that a thorough understanding of their morphology will greatly contribute to the knowledge of the evolutionary history and the origin of diversity for the major osteichthyan clades. To this end, we examined comparative developmental series from the pectoral girdle in Acipenser fulvescens, A. medirostris, A. transmontanus, and Scaphirhynchus albus to document, describe, and compare ontogenetic and allometric differences in the pectoral girdle. We find, not surprisingly, broad congruence between taxa in the basic pattern of development of the dermal and chondral elements of the pectoral girdle. However, we also find clear differences in the details of structure and development among the species examined in the dermal elements, including the clavicle, cleithrum, supracleithrum, posttemporal, and pectoral‐fin spine. We also find differences in the internal fin elements such as the distal radials as well as in the number of fin rays and their association with the propterygium. Further, there are clear ontogenetic differences during development of the dermal and chondral elements in these species and allometric variation in the pectoral‐fin spine. The characters highlighted provide a suite of elements for further examination in studies of the phylogeny of sturgeons. Determining the distribution of these characters in other sturgeons may aid in further resolution of phylogenetic relationships, and these data highlight the role that ontogenetic and comparative developmental studies provide in systematics. J. Morphol. 276:241–260, 2015. © 2014 Wiley Periodicals, Inc.     

On the osteology and myology of catfish pectoral girdle, with a reflection on catfish (Teleostei: Siluriformes) plesiomorphies

The configuration of the pectoral girdle bones and muscles of numerous catfishes was studied in detail and compared with that of other siluriforms, as well as of other teleosts, described in the literature. The pectoral girdle of catfishes is composed of only three bones, which probably correspond to the posttemporo-supracleithrum (posttemporal + supracleithrum), scapulo-coracoid (scapula + coracoid), and cleithrum of other teleosts. These latter two bones constitute the place of origin of the pectoral girdle muscles. Two of these muscles are related to the movements of the pectoral fin. These two muscles correspond, very likely, to the abductor superficialis and to the adductor superficialis of other teleostean fishes. In relation to the pectoral spine (thickened first pectoral fin ray), it is usually moved by three well-developed muscles, which are probably homologous with the arrector ventralis, arrector dorsalis, and abductor profundus of nonsiluriform teleosts. The morphological diversity and the plesiomorphic configuration of these muscles, as well as of the other catfish pectoral girdle structures, are discussed.     

Development of the paired fins in the paddlefish, Polyodon spathula

In Polyodon spathula, the pectoral fin radials, with the exception of the metapterygium, are derived from the decomposition of a single continuous cartilage fin plate that is continuous with the scapulocoracoid. This cartilage sheet develops two interior splits to form three precursor pieces, and these decompose in a predictable way to generate the propterygium and radials. The metapterygium is an extension of the scapulocoracoid that segments off of it during early development. To our knowledge, this has not been reported for acipenserids or other basal actinopterygians. In teleosts, the proximal radials also develop from the "break up" of an initially continuous paddle-like sheet of cartilage along the posterior edge of the scapulocoracoid, and in Polypterus and sharks a similar pattern holds. Thus, the pattern observed in Polyodon may represent the basal developmental condition for the gnathostome pectoral fin. The process underlying development of the superficially similar cartilages of the pelvic and pectoral fins is different. In the pectoral fin, the metapterygium is segmented off of the scapulocoracoid and other radials form from the decomposition of the cartilage plate. In contrast, individual rod-like basipterygial elements form in a close one-to-one correspondence with the middle radials of the pelvic fin, but later fuse to form an anterior element that is branched in appearance. To evaluate further claims of similarity among the pectoral and pelvic fin elements of various fishes, the course of the development of these structures must be observed. The pectoral fin and girdle in Polyodon ossifies in a different sequence than that proposed as ancestral (and highly conserved) for actinopterygians: the supracleithrum ossifies significantly before the cleithrum. The later ossification of the cleithrum in Polyodon may be related to the primary use of the caudal fin vs. the pectoral fins in their locomotion.     

Fossils and Strata

Jessen, H. L.: Schultergürtel und Pectoralflosse hci Actinopterygiern. [Shoulder girdle and pectoral fin in actinopterygians.] Fossils and Strata , Number 1, pp. 1–101, Pls. 1–25. Oslo, 5th May 1972.
The anatomy of the shoulder girdle and pectoral fin is investigated in adults and larvae of Asperser, Amia, Lepisosteus, Elops, Salmo , and Polypterus . In comparison with similar structures in other gnathostomian fishes these studies yielded certain conclusions as concerns the interrelationships of the recent actinopterygian groups and the affinities of the hrachiopterygians, the latter by this evidence belonging to an evolutionary line of their own. With regard to actinopterygian phylogeny, a comparison with the shoulder girdle and pectoral fin in fossil forms, including Chondrosteus, Moythomoasia, Palaeoniscus, Pteronisculus, Pachycormus, Catarus, Hypsocormus , and Birzeria , shows that teleosteans presumably are closer to chondrosteans than holosteans, and that holosteans seem to have branched off comparatively early from the actinopterygian stem.     

Comparative morphology and osteology of pelvic fin‐derived midline suckers in lumpfishes,snailfishes and gobies

Some fishes use modified body structures – including pelvic fins – to produce suction to facilitate stability in turbulent environments. This study compares the morphology and osteology of the pelvic suckers of representative lumpfishes (Cyclopteridae), snailfishes (Liparidae) and gobies (Gobiidae). In all species studied the midline sucker (pelvic suctorial organ [PSO]) is formed from the pelvic girdle and fin rays I and 5 of the pelvic fins, comprised of similar osteological elements to those found in the pelvic girdle and pelvic fin rays although the morphology of the bony elements is species‐specific. Pelvic suctorial organs in those fishes that lack pelvic girdles are therefore homologous to pelvic girdles. The phenotypic diversity seen in so few species indicates that many sucker morphologies have arisen, origination depending on the concerted development of muscular, skeletal, nervous, and skin body tissues. The structure of the soft rays of the pelvic fins in the liparids and cyclopterids is unusual and indicative of unconventional developmental patterning of fin ray halves and of evolution in the underlying mechanisms responsible for the development of midline suckers.     

Bony‐toothed birds (Aves: Pelagornithidae) from the Middle Eocene of Belgium

Abstract: We describe well‐preserved remains of the Pelagornithidae (bony‐toothed birds) from the middle Eocene of Belgium, including a sternum, pectoral girdle bones and humeri of a single individual. The specimens are tentatively assigned to Macrodontopteryx oweni Harrison and Walker, 1976 , which has so far only been known from the holotype skull and a referred proximal ulna. Another species, about two times larger, is represented by an incomplete humerus and tentatively identified as Dasornis emuinus ( Bowerbank, 1854 ). The fossils provide critical new data on the osteology of the pectoral girdle of bony‐toothed birds. For the first time, the sternum of one of the smaller species is preserved, and this bone exhibits a more plesiomorphic morphology than the recently described sternum of the giant Miocene taxon Pelagornis. The coracoid resembles that of the Diomedeidae (albatrosses) in overall morphology, but because bony‐toothed birds lack apomorphies of the Procellariiformes, the similarities are almost certainly owing to convergence. Bony‐toothed birds were often compared with the ‘Pelecaniformes’ by previous authors, who especially made comparisons with the Sulidae (gannets and boobies). However, the coracoid distinctly differs from that of extant ‘pelecaniform’ birds, and the plesiomorphic presence of a foramen nervi supracoracoidei as well as the absence of a well‐delimited articulation facet for the furcula supports a position outside the Suloidea, the clade to which the Sulidae belong.     

Fossil fishes from china provide first evidence of dermal pelvic girdles in osteichthyans

Background

The pectoral and pelvic girdles support paired fins and limbs, and have transformed significantly in the diversification of gnathostomes or jawed vertebrates (including osteichthyans, chondrichthyans, acanthodians and placoderms). For instance, changes in the pectoral and pelvic girdles accompanied the transition of fins to limbs as some osteichthyans (a clade that contains the vast majority of vertebrates – bony fishes and tetrapods) ventured from aquatic to terrestrial environments. The fossil record shows that the pectoral girdles of early osteichthyans (e.g., Lophosteus, Andreolepis, Psarolepis and Guiyu) retained part of the primitive gnathostome pectoral girdle condition with spines and/or other dermal components. However, very little is known about the condition of the pelvic girdle in the earliest osteichthyans. Living osteichthyans, like chondrichthyans (cartilaginous fishes), have exclusively endoskeletal pelvic girdles, while dermal pelvic girdle components (plates and/or spines) have so far been found only in some extinct placoderms and acanthodians. Consequently, whether the pectoral and pelvic girdles are primitively similar in osteichthyans cannot be adequately evaluated, and phylogeny-based inferences regarding the primitive pelvic girdle condition in osteichthyans cannot be tested against available fossil evidence.

Methodology/Principal Findings

Here we report the first discovery of spine-bearing dermal pelvic girdles in early osteichthyans, based on a new articulated specimen of Guiyu oneiros from the Late Ludlow (Silurian) Kuanti Formation, Yunnan, as well as a re-examination of the previously described holotype. We also describe disarticulated pelvic girdles of Psarolepis romeri from the Lochkovian (Early Devonian) Xitun Formation, Yunnan, which resemble the previously reported pectoral girdles in having integrated dermal and endoskeletal components with polybasal fin articulation.

Conclusions/Significance

The new findings reveal hitherto unknown similarity in pectoral and pelvic girdles among early osteichthyans, and provide critical information for studying the evolution of pelvic girdles in osteichthyans and other gnathostomes.     

Comparative anatomy and development of pectoral and pelvic girdles in hylid anurans

The development of the tetrapod pectoral and pelvic girdles is intimately linked to the proximal segments of the fore‐ and hindlimbs. Most studies on girdles are osteological and provide little information about soft elements such as muscles and tendons. Moreover, there are few comparative developmental studies. Comparative data gleaned from cleared‐and‐stained whole mounts and serial histological sections of 10 species of hylid frogs are presented here. Adult skeletal morphology, along with bones, muscles, and connective tissue of both girdles and their association with the proximal portions of the anuran fore‐ and hindlimbs are described. The data suggest that any similarity could be attributable to the constraints of their ball‐and‐socket joints, including incorporation of the girdle and stylopodium into a single developmental module. An ancestral state reconstruction of key structures and developmental episodes reveals that several development events occur at similar stages in different species, thereby preventing heterochronic changes. The medial contact of the halves of the pectoral girdle coincides with the emergence of the forelimbs from the branchial chamber and with the total differentiation of the linkage between the axial skeleton and the girdles. The data suggest that morphogenic activity in the anterior dorsal body region is greater than in the posterior one, reflecting the evolutionary sequence of the development of the two girdles in ancient tetrapods. The data also document the profound differences in the anatomy and development of the pectoral and pelvic girdles, supporting the proposal that the pectoral and pelvic girdles are not serially homologous, as was long presumed.     

Pectoral fin and girdle development in the basal actinopterygians Polyodon spathula and Acipenser transmontanus

The pectoral fins of Acipenseriformes possess endoskeletons with elements homologous to both the fin radials of teleosts and the limb bones of tetrapods. Here we present a study of pectoral fin development in the North American paddlefish, Polyodon spathula, and the white sturgeon, Acipenser transmontanus, which reveals that aspects of both teleost and tetrapod endoskeletal patterning mechanisms are present in Acipenseriformes. Those elements considered homologous to teleost radials, the propterygium and the mesopterygial radials, form via subdivision of an initially chondrogenic plate of mesenchymal cells called the endoskeletal disc. In Acipenseriformes, elements homologous to the sarcopterygian metapterygium develop separately from the endoskeletal disc as an outgrowth of the endoskeletal shoulder girdle that extends into the posterior margin of the finbud. As in tetrapods, the elongating metapterygium and the metapterygial radials form in a proximal to distal order as discrete condensations from initially nonchondrogenic mesenchyme. Patterns of variation seen in the Acipenseriform fin also correlate with putative homology: all variants from the "normal" fin bauplan involved the metapterygium and the metapterygial radials alone. The primary factor distinguishing Polyodon and Acipenser fin development from each other is the composition of the endoskeletal extracellular matrix. Proteoglycans (visualized with Alcian Blue) and Type II collagen (visualized by immunohistochemistry) are secreted in different places within the mesenchymal anlage of the fin elements and girdle and at different developmental times. Acipenseriform pectoral fins differ from the fins of teleosts in the relative contribution of the endoskeleton and dermal rays. The fins of Polyodon and Acipenser possess elaborate endoskeletons overlapped along their distal margins by dermal lepidotrichia. In contrast, teleost fins generally possess relatively small endoskeletal radials that articulate with the dermal fin skeleton terminally, with little or no proximodistal overlap.     

Chondrogenesis and ossification of the lissamphibian pectoral girdle

Knowledge of amphibian shoulder development is requisite for further understanding of gnathostome pectoral girdle evolution. Fish and amniotes share few pectoral girdle elements, but modern amphibians exhibit a unique combination of traits that bridge the morphological gap between these two groups. I analyzed patterns of chondrogenesis, ossification, and bone histology of the pectoral girdles of two anuran species (Xenopus laevis and Bombina orientalis) and two urodele species (Ambystoma mexicanum and Desmognathus aeneus) to provide new insight into the evolution of the tetrapod pectoral girdle. Comparisons reveal the following: 1) variation in the pattern of chondrogenesis among the anuran species analyzed correlates to variation in adult pectoral girdle morphology; 2) morphologically similar pectoral skeletons do not necessarily have similar patterns of bone histology; and 3) the urodele and anuran pectoral girdles included herein share a common morphology despite differences in patterns of chondrogenesis.     

Molecular evolution of the neurohypophysial hormones: The active peptides of a primitive bony fish Polypterus bichir

Neurohypophysial hormones have been so far identified in Neopterygii and Crossopterygii but not in species of the bird sub-class of bony fishes, the Palaeopterygii. Isolation and chemical characterization of the active principles of a primitive bony fish, Polypterus bichir, have been performed. Isotocin (Ser(4)-Ile(8)-oxytocin) and arginine vasotocin (Arg(8)-oxytocin) have been identified. Because the same peptides were found in the recent Neopterygii, it can be deduced that neurohypophysial hormones have displayed a peculiar stability in the course of the evolution of bony fishes. However isotocin and vasotocin are replaced by oxytocin and vasopressins in mammals and therefore might be regarded as "old" molecules.     

Development of zebrafish (Danio rerio) pectoral fin musculature

During posthatching development the fins of fishes undergo striking changes in both structure and function. In this article we examine the development of the pectoral fins from larval through adult life history stages in the zebrafish (Danio rerio), describing in detail their pectoral muscle morphology. We explore the development of muscle structure as a way to interpret the fins' role in locomotion. Genetic approaches in the zebrafish model are providing new tools for examining fin development and we take advantage of transgenic lines in which fluorescent protein is expressed in specific tissues to perform detailed three-dimensional, in vivo fin imaging. The fin musculature of larval zebrafish is organized into two thin sheets of fibers, an abductor and adductor, one on each side of an endoskeletal disk. Through the juvenile stage the number of muscle fibers increases and muscle sheets cleave into distinct muscle subdivisions as fibers orient to the developing fin skeleton. By the end of the juvenile period the pectoral girdle and fin muscles have reoriented to take on the adult organization. We find that this change in morphology is associated with a switch of fin function from activity during axial locomotion in larvae to use in swim initiation and maneuvering in adults. The examination of pectoral fins of the zebrafish highlights the yet to be explored diversity of fin structure and function in subadult developmental stages. J. Morphol. (c) 2005 Wiley-Liss, Inc.     

The Developmental Basis of Skeletal Cell Differentiation and the Molecular Basis of Major Skeletal Defects

Vertebrate skeletal differentiation retains elements from simpler phyla, and reflects the differentiation of supporting tissues programmed by primary embryonic development. This developmental scheme is driven by homeotic genes expressed in sequence, with subdivision of skeletal primordia driven by a combination of seven transmembrane‐pass receptors responding to Wnt‐family signals, and by bone morphogenetic family signals that define borders of individual bones. In sea‐dwelling vertebrates, an essentially complete form of the skeleton adapted by the land‐living vertebrates develops in cartilage, based on type II collagen and hydrophilic proteoglycans. In bony fishes, this skeleton is mineralized to form a solid bony skeleton. In the land‐living vertebrates, most of the skeleton is replaced by an advanced vascular mineralized skeleton based on type I collagen, which reduces skeletal mass while facilitating use of skeletal mineral for metabolic homeostasis. Regulation of the mammalian skeleton, in this context, reflects practical adaptations to the needs for life on land that are related to ancestral developmental signals. This regulation includes central nervous system regulation that integrates bone turnover with overall metabolism. Recent work on skeletal development, in addition, demonstrates molecular mechanisms that cause developmental bone diseases.     

Expression of Hoxa-11 and Hoxa-13 in the pectoral fin of a basal ray-finned fish, Polyodon spathula: implications for the origin of tetrapod limbs

Summary Paleontological and anatomical evidence suggests that the autopodium (hand or foot) is a novel feature that distinguishes limbs from fins, while the upper and lower limb (stylopod and zeugopod) are homologous to parts of the sarcopterygian paired fins. In tetrapod limb development Hoxa-11 plays a key role in differentiating the lower limb and Hoxa-13 plays a key role in differentiating the autopodium. It is thus important to determine the ancestral functions of these genes in order to understand the developmental genetic changes that led to the origin of the tetrapod autopodium. In particular it is important to understand which features of gene expression are derived in tetrapods and which are ancestral in bony fishes. To address these questions we cloned and sequenced the Hoxa-11 and Hoxa-13 genes from the North American paddlefish, Polyodon spathula, a basal ray-finned fish that has a pectoral fin morphology resembling that of primitive bony fishes ancestral to the tetrapod lineage. Sequence analysis of these genes shows that they are not orthologous to the duplicated zebrafish and fugu genes. This implies that the paddlefish has not duplicated its HoxA cluster, unlike zebrafish and fugu. The expression of Hoxa-11 and Hoxa-13 in the pectoral fins shows two main phases: an early phase in which Hoxa-11 is expressed proximally and Hoxa-13 is expressed distally, and a later phase in which Hoxa-11 and Hoxa-13 broadly overlap in the distal mesenchyme of the fin bud but are absent in the proximal fin bud. Hence the distal polarity of Hoxa-13 expression seen in tetrapods is likely to be an ancestral feature of paired appendage development. The main difference in HoxA gene expression between fin and limb development is that in tetrapods (with the exception of newts) Hoxa-11 expression is suppressed by Hoxa-13 in the distal limb bud mesenchyme. There is, however, a short period of limb bud development where Hoxa-11 and Hoxa-13 overlap similarly to the late expression seen in zebrafish and paddlefish. We conclude that the early expression pattern in tetrapods is similar to that seen in late fin development and that the local exclusion by Hoxa-13 of Hoxa-11 from the distal limb bud is a derived feature of limb developmental regulation.     

Mouth development in the Senegal bichir Polypterus senegalus does not involve the oropharyngeal membrane: possible implications for the ecto‐endoderm boundary and tooth initiation

Polypterid fishes are considered the basal‐most group of extant actinopterygians and thus may serve as a direct link to understand the evolution of the first bony fishes. Embryonic and larval specimens, however, are extremely scarce, making it difficult to study their developmental patterns and processes. During the past few years we collected many embryos and larvae of the Senegal bichir Polypterus senegalus and in this paper we describe some novel observations concerning the supposed ecto‐endoderm border in the mouth and consecutive initiation of dental development. The mouth of the Senegal bichir does not develop via a classical oropharyngeal membrane but instead, opening the mouth occurs via a separation of the upper and lower jaws that are connected by epithelial bridges. These structures are bilaterally symmetrical and are found invariantly at places of the earliest tooth bud development. It is suggested that the epithelial bridges may represent the ecto‐endoderm bordering zone, are both structurally and functionally homologous to the oropharyngeal membrane and consequently it is hypothesized that the epithelial bridges and the developmental factors producing them play a key role in initiation and early distribution of the particular dental domains.     

Morphological evidence supporting the monophyly of the family Polynemidae (Teleostei: Perciformes) and its sister relationship with Sciaenidae

The monophyly of Polynemidae was evaluated and its sister relationship with Sciaenidae discussed, based on osteological and myological characters from 24 polynemid species in eight genera, with comparisons with acanthomorph fishes from literature and 86 species in 8 orders and 63 families examined. Polynemidae was inferred as a monophyletic group, strongly supported by 19 synapomorphies, including four unique characters (unnamed bone present on cephalic sensory canal extending from supratemporal, third actinost not supporting pectoral-fin rays, section A1 comprising lateral and medial elements, and division of obliquus inferioris present between lower postcleithrum and rod-like process on coracoid) in percoids. In addition, seven pectoral girdle characters were recognized, with the girdle possessing filament-like sensory rays, an adaptation to benthic life in muddy water. The sister relationship of Polynemidae and Sciaenidae was supported by six synapomorphies, including two rather rare (a single branchiostegal ray suspended by epihyal and posterior portions of pelvic bones on both sides interdigitated) and two unique characters (metapterygoid and quadrate interdigitated medially and anterior extension of the nasal canal).