The prenatal development of the human nasal and vomeral bones

The purpose of the present study was to establish normal prenatal development standards for the nasal and vomeral bones, both formed by intramembranous ossification in the membrane covering the cartilaginous nasal capsule. The study is based upon a combination of macroscopic (devisceration and radiography) and microscopic (histology) analyses on 62 normal human fetuses from spontaneous and induced abortions, ranging in gestational age from 9 to 24 weeks, representing crown-rump lengths (CRL) from 33 to 225 mm. Special attention was paid to the onset of bone formation in relation to other maturity aspects and to the growth of the bones. The very first onset of ossification of the vomeral bone is observed as two bilateral ossification centers, prior to nasal bone ossification. Later, the two bilateral ossification centers fuse caudally below the cartilaginous nasal septum, thus changing into a U-shaped bone when observed in the coronal plane. By bony apposition caudally the U-shaped vomer gradually changes into a Y-shape. The nasal bone appears as a thin bony contour ventral to the cartilaginous nasal septum in the sagittal plane, and changes gradually during growth to a wedge-shaped bone. Knowledge of the early development of the internal nose (vomeral bone) and external nose (nasal bone) is significant in understanding mid-face congenital malformations.

A primary cell culture system of luteinizing hormone releasing hormone neurons derived from embryonic olfactory placode in the rhesus monkey

The purpose of this study is to establish a primary LHRH cell culture system using embryonic olfactory placode and to examine whether LHRH cells derived from olfactory placode and the migratory pathway of LHRH neurons mature in vitro. Six monkey fetuses at the ages of E34-E36 were delivered surgically and the area including the olfactory placode (PL) and the areas that encompass the migratory pathway (MP) were dissected out. The tissues were cut into small pieces and plated on collagen- or poly-L-lysine-coated glass coverslips in medium M199. Cultures were maintained for up to 33 days and immunostained for LHRH, GnRH-associated peptide, neurofilament protein, neuron-specific enolase, and glial fibrillary acidic protein. LHRH positive cells were also positive for neurofilament proteins neuron-specific enolase, and GnRH-associated peptides, but negative for glial fibrillary acidic protein. In the first week of culture, LHRH cells remained within the explants of PL, were rounded (average dimensions: 13.0 x 11.3 microns) and stained lightly. By the second week a number of LHRH cells (15.7 x 13.6 microns) with neurites started to migrate out from PL explants, whereas some still remained in the PL. By the third week a large number of LHRH cells (19.3 x 9.4 microns) had migrated out from the PL. They were fusiform in shape with clear nuclei and extended long varicose neurites up to 500 microns in length. A few "pioneer" LHRH cells appeared to lead the migration of 100-400 LHRH cells forming 1-3 major migratory paths. In contrast, LHRH cells from MP explants migrated out sooner than those from PL explants. LHRH cells from the ventral part of the MP, which is close to the PL, migrated out by 1-2 weeks and formed several migratory paths, whereas LHRH cells from the dorsal part of the MP, which is farther from the PL, were scattered widely around explants and their neurites were extended tortuously. Cultured LHRH cells released LHRH into the media and responded to challenge with high K+. The results indicate that 1) primary LHRH neurons can be obtained from the embryonic PL and their migratory pathway, 2) these neurons migrate and mature in culture and 3) they are accessible for cellular and molecular studies.

The vomeronasal duct has a protracted postnatal development in the mouse

Recent evidence suggests that the accessory olfactory system (AOS) may mediate chemoreception before birth. Such a capability may allow the fetus to begin to sample chemical stimuli from the outside world, a possibility that has important developmental and evolutionary implications. Herein we describe the development in the mouse of the duct that connects the vomeronasal organ (VNO), containing the primary receptor neurons of the AOS, with the nasal cavity and thus with external stimuli. Twenty-four mice, four at each of six different ages from the last day of gestation through 25 days of age, were fixed and embedded in glycol methacrylate. Serial sections were examined under the light microscope so that the VNO duct could be reconstructed in three dimensions. Results confirm an earlier study which demonstrated that the VNO duct is not patent before birth. The duct becomes patent sometime after the first day of life but remains in an immature condition throughout the normal prepubertal period. During this period the duct is characterized by an internal surface that is rapidly desquamating such that the lumen of the duct contains sloughed tissue. These results suggest that the VNO is unlikely to function in the prenatal period, since the route for external stimuli to reach its receptor surface is blocked. The protracted period of VNO duct development reported here is consistent with the great bulk of data on the AOS of mammals which firmly establishes its role in the detection of pheromones which coordinate reproduction.

Initiation of secondary cartilage in the mandible of the Syrian hamster in the absence of muscle function

The functioning lower jaw is a prerequisite of the ongoing secondary chondrogenesis in the mammalian mandibular condyle. Does the articular function also initiate secondary chondrogenesis in the mandible? The angular process of the fetal mammalian mandible possesses a large secondary cartilage without any apparent articular function. Past studies have shown that the anlage of the lower jaw of the mouse embryo grown in organ culture produces condylar and angular cartilages as in vivo. In order to clarify further the capacity of the mandibular anlage to initiate secondary chondrogenesis in a non-functional environment, mandibular arch explants taken from the prenatal hamster before any cartilage or bone formation was apparent were grown in organ culture. Both primary and secondary cartilage could be found in them within 9-10 days. The results thus indicate that initiation of the condylar and/or angular secondary cartilaginous development in the rodent mandible occurs in the absence of jaw-opening function, although the pertinent literature indicates that function maintains cartilaginous differentiation in the condyle.

[Distribution of type IV collagen, laminin and fibronectin during naris formation in the chick embryo]

The presence and distribution of extracellular matrix (ECM) macromolecules were analyzed in the facial primordia of chick embryos from stages (22-28) of development corresponding to naris formation. Frozen sections through the nasal placode, medial nasal processes and lateral nasal processes were prepared for indirect immunofluorescence employing a biotin-avidin DCS system using monoclonal antibodies against type IV collagen, laminin and fibronectin. The results demonstrated that ECM played a very important role in regulating migration, adhesion and anchorage of cells during morphogenesis. Strong fluorescence of basal lamina was present in the areas of rapid ingrowth of the nasal placode. It was suggested that ECM has very important guiding and regulating role during naris formation in chick embryo.

Distribution of F-actin during mouse facial morphogenesis and its perturbation with cytochalasin D using whole embryo culture

Histological and experimental studies were performed in mouse embryos to elucidate possible roles of actin filaments in the nasal epithelium during facial morphogenesis. C57BL/6 mouse embryos (8.5-11.5 days of gestation) were fixed and frozen sections were stained with rhodamine-phalloidin. Before formation of the nasal placode, there was no specific localization of F-actin. After the nasal placode was formed, intense staining of F-actin was observed at the apical side of the placode. Conversely, it was located at the basal side of the epithelium of developing nasal prominences. By using the whole embryo culture system, perturbation experiments were conducted with cytochalasin D (CD), which inhibits the polymerization of actin filaments. When day-10 embryos were exposed to CD at several concentrations for 24 hr, fusion of nasal prominences was inhibited in a dose-dependent manner. Treatment with a high dose of CD for 2 hr also prevented the same development irreversibly. In contrast, when day-9 embryos were exposed to CD at several concentrations for 24 hr, invagination of the nasal placode was not perturbed at all. The results suggest that apical F-actin plays an essential role in maintaining the close apposition state of the nasal prominences and in the following fusion. During the invagination stage, F-actin might be important in maintaining the epithelial structure, but is not crucial to the initiation of placode invagination.

Immunocytochemical demonstration of neural cell adhesion molecule (NCAM) along the migration route of luteinizing hormone-releasing hormone (LHRH) neurons in mice

Contact between the developing forebrain and the ingrowing central processes of the olfactory, vomeronasal and terminal nerves is preceded by a migration of neural cell adhesion molecule (NCAM)-immunoreactive cells from the epithelium of the olfactory pit and the formation of an NCAM-immunoreactive cellular aggregate in the mesenchyme between the olfactory pit and the forebrain. The axons of the olfactory, vomeronasal, and terminal nerves, also NCAM-immunoreactive, grow into the cellular aggregate, which as development proceeds, becomes continuous with the rostral tip of the forebrain. The lateral and more rostral part of the cellular aggregate receives the ingrowing axons of the olfactory nerves and becomes the olfactory nerve layer of the olfactory bulb. The medial, more caudal part receives the central processes of the vomeronasal and terminal nerves. The vomeronasal nerve ends in the accessory olfactory bulb. The central processes of the terminal nerve end in the medial forebrain. Luteinizing hormone-releasing hormone (LHRH)-immunoreactive neurons, like the vomeronasal and terminal nerves, originate from the medial part of the olfactory pit. These LHRH cells migrate into the brain along and within a scaffolding formed by the NCAM-immunoreactive axons of the vomeronasal and terminal nerves, and they are never seen independent of this NCAM scaffold as they cross the nasal lamina propria. The results suggest that: (1) NCAM is likely to be necessary for scaffold formation, and (2) the scaffold may be essential for the subsequent migration of LHRH neurons into the brain. Because they aggregate, migrating LHRH-immunoreactive neurons, on which we did not detect NCAM immunoreactivity, may interact via other cell adhesion molecules (CAM). Inasmuch as the interaction between the LHRH-immunoreactive neurons and the NCAM-immunoreactive scaffold is heterotypic, the possibility of a heterophilic (NCAM to other CAM) interaction is not ruled out. These findings focus our attention on the functional role of NCAM in this migratory system.

Morphometric analysis of heterozygote dancer mice predisposed to 6-aminonicotinamide-induced cleft lip

Mid-facial development is an extremely complex process involving coordinated events and precise timing. Cleft lip (CL) may result from the failed fusion of the lateral and medial nasal processes in the developing embryo. It has been postulated that spontaneous CL in the A/J strain of mice may be due to a predisposing face shape (Trasler, '68). This hypothesis was examined in mutant mice susceptible to teratogen-induced CL. Mice carrying the dancer (Dc) mutation in the heterozygous state rarely develop CL, whereas 90% of homozygotes (Dc/Dc) develop CL. Outcrossed heterozygotes show elevated susceptibility to 6-aminonicotinamide (6AN)-induced CL (Trasler et al., '84) and these were used to investigate face shape as a predisposing factor. Dc/+ and +/+ males were mated to R stock females, and embryos were collected on day 10/21 hr, when the nasal placodes are approximately at the oblong or crescent stage. Total nasal process areas and volumes, medial and lateral process areas and volumes, and medial jut lengths were measured from histological sections, and comparisons made between the two populations. The results indicate that compared to +/+ control, heads of embryos from the Dc/+ cross have significantly smaller mean total process areas and volumes (P less than 0.005), mean lateral process areas and volumes (P less than 0.005), mean medial process area and volumes (P less than 0.01), mean maximum head diameter (P less than 0.02), but similarly sized medial juts and crown rump lengths. Correlations between maximum head diameter and process size indicate that the Dc mutation may hinder normal development of the nasal processes. These reduced nasal processes may explain the underlying predisposition to 6AN-induced CL.

Morphological study of fetal nasopharyngeal epithelium in man

In 30 human fetuses between 8 and 13 weeks of intrauterine life the lateral wall of the nasopharynx was examined by light microscopy and transmission and scanning electron microscopy. In the subjects between 8 and 9 weeks in utero the mucosa displays still an immature appearance, being mono- or bistratified and lacking the characteristic structures of the respiratory epithelium. Nevertheless, signs of differentiation are to be noticed, with the presence of two distinct cellular types that, in the later periods, will give rise to ciliated cells and microvillus-provided cells. An almost complete differentiation will be reached at 12-13 weeks in utero, even if goblet cells are still lacking in the examined zone during the considered period. Nonrespiratory types of epithelium, such as transitional or squamous, were never found in the studied subjects.

Developmental correlates of midfacial components in a normal and cleft lip and palate human fetal sample

Midfacial hypoplasia in patients with complete clefts of the lip and palate is considered to be the result of congenital dysmorphogenesis combined with surgical effects. The present study describes congenital correlates of midfacial hypoplasia by examining the relationships between premaxillary size and a number of adjacent oronasal capsular components in a sample of second trimester normal and complete cleft fetal specimens. Midfacial relationships from previously published data from 3-D computer reconstructions of histologic material were assessed by multiple regression and path analyses. Stepwise multiple regression analysis revealed that the combination of age (body size) and nasal septal length were the best predictor variables of premaxillary length and accounted for 90 percent and 93 percent (p less than .01) of the variance in normal and cleft fetal specimens, respectively. Tongue length was seen to slightly increase the R2 values in the cleft, but not the normal sample. Path analysis results revealed that with body size held constant, nasal capsule volume explained only 3 percent of premaxillary variance, while septal length accounted for approximately 45 percent of the variance (p less than .05). Results show that the relationships of the midfacial components in the cleft fetal sample closely followed normal second-trimester midfacial growth patterns and suggest that the septal-traction model may be a more parsimonious and primary explanatory mechanism of early midfacial growth than the functional matrix model in both normal and complete cleft fetal specimens.

Subdivisions of the terminal nerve in Xenopus laevis

The majority of recent studies on the terminal nerve (nt) in various vertebrates either involved tracer injections into the nasal cavity or made use of the LHRH-/FMRFamide-like immunoreactivity (ir) of a portion of its fibers. The present investigation was designed to determine the extent of overlap between data rendered by the two methods in Xenopus. The findings reveal no overlap of nt projections visualized by the two experimental techniques. This result sheds doubt on the validity of current definitions of the nt system.

The embryonic development of the lateral nasal wall from 8 to 24 weeks

This histological study of 20 fetal heads aged between 8 and 24 weeks of gestation demonstrates and describes the embryonic development of the lateral wall of the nose. The three turbinates (inferior, middle, and superior) arise as soft-tissue swellings (preturbinates) by 8 weeks' gestation. A cartilage capsule surrounds the nose at 8 weeks and by 9 weeks, medially directed flanges of cartilage have invaded all three preturbinates. The uncinate process arises from the medial surface of the lateral cartilaginous capsule and is first identifiable by 10 weeks. An "air space" progressively develops from 11 to 12 weeks lateral to the cartilaginous uncinate process and from this space, the embryonic channel to the maxillary sinus develops. The embryonic woven bone of the maxilla can be identified from 9 to 10 weeks and enlarges both absolutely and relatively to the nasal cavity, so that by 13 to 14 weeks, this expanding bone forms the lateral wall of the inferior meatus as the cartilaginous nasal capsule regresses.

Applied nasal anatomy & embryology

The embryology & anatomy of the nose as it is applied to rhinoplasty is surveyed so that the surgeon in training can develop a basis from which to review the literature. This review demonstrates the need for the consolidation and clarification of the nomenclature associated with the complex anatomy of the nasal pyramid.

Size and growth rate of the tongue in normal and cleft lip and palate human fetal specimens

In the present study, the size and rate of growth of the tongue was assessed in human fetuses. For comparative purposes, 29 human fetal specimens (20 "normal" and 9 with cleft lip and palate were celloidin embedded, sectioned, stained with hematoxylin and eosin, and serially photomicrographed. The specimens ranged from 8 to 21 weeks postmenstrual age. The application of a well documented three-dimensional reconstruction technique provided quantification of several aspects of the tongue. Tongue length and volume were larger in the cleft specimens than for the normal specimens, while both length and volume were growing at a faster rate. Growth curves were produced by plotting length and volume against postmenstrual age and a significant difference was noted between the slopes (growth rate) of the growth curves for tongue length and volume for the two groups. Tongue length increase was approximately 2.27 times greater and tongue volume increase was approximately 1.64 times more for the cleft specimens than for the normal specimens from 8 to 21 weeks. In support of these findings, tongue volume was relatively larger expressed as a contribution of total oronasal capsule volume in the cleft specimens. For an initial age category (8 to 12 weeks), tongue volume in the cleft specimens was larger, growing at a faster rate than normal tongue volume and a significant difference was noted between the slopes of the growth curves. No significant difference was observed between the tongue length indices in the initial or the 8 to 21 week age category.(ABSTRACT TRUNCATED AT 250 WORDS)

Chick frontonasal process excision significantly affects mid-facial development

The midfacial region in vertebrates may be considered as developing from five separate processes, namely the central frontonasal process (FNP) and the paired maxillary and lateral nasal processes. Relatively little is known about the mechanisms whereby these processes interact to produce structures of the neonatal/adult face. This study was undertaken to gain some insights into the events involved in this process, and involved observing the effects on facial development in the chick of surgical excision of the FNP, prior to its fusion with the other facial processes. In the absence of the FNP, outgrowth of the upper beak was dramatically reduced, agenesis of the primary palate occurred, and development of the maxillary processes and palatal shelves was impaired. Thus, in the chick, the frontonasal process plays a major role in midfacial morphogenesis. Not only does the FNP provide the primary palate and a contribution to the development of the nasal septum, it is also important in the ordered development of the maxillary processes and of the definitive secondary palate--contributions which have not emerged clearly from in vitro and teratogenic studies.

Developmental expression of syndecan, an integral membrane proteoglycan, correlates with cell differentiation

Syndecan is an integral membrane proteoglycan that behaves as a matrix receptor by binding cells to interstitial matrix and associating intracellularly with the actin cytoskeleton. Using immunohistology, we have now localized this proteoglycan during the morphogenesis of various derivatives of the surface ectoderm in mouse embryos. Syndecan is expressed on ectodermal epithelia, but is selectively lost from the cells that differentiate into the localized placodes that initiate lens, nasal, otic and vibrissal development. The loss is transient on presumptive ear, nasal and vibrissal epithelia; the derivatives of the differentiating ectodermal cells that have lost syndecan subsequently re-express syndecan. In contrast, syndecan is initially absent from the mesenchyme underlying the surface ectoderm, and is transiently expressed when the surface ectoderm loses syndecan. These results demonstrate that expression of syndecan is developmentally regulated in a distinct spatiotemporal pattern. On epithelia, syndecan is lost at a time and, location that correlates with epithelial cell differentiation and, on mesenchyme, syndecan is acquired when the cells aggregate in proximity to the epithelium. This pattern of change with morphogenetic events is unique and not duplicated by other matrix molecules or adhesion receptors.

The migration of luteinizing hormone-releasing hormone (LHRH) neurons from the medial olfactory placode into the medial basal forebrain

Over the years, investigators have noticed, in a wide variety of species of vertebrates, large numbers of cells migrating from the olfactory placode to the forebrain. These cells were considered to be Schwann cells or ganglion cells of the terminalis nerve. Recently, immunocytochemical localization studies have shown that many of these migrating cells contain luteinizing hormone-releasing hormone (LHRH), a brain peptide that regulates reproductive functions by evoking the release of luteinizing hormone and follicle-stimulating hormone from the anterior pituitary gland. The origin of LHRH cells in the epithelium of the medial olfactory placode, their migration across the nasal septum and into the forebrain, with branches of the terminalis nerve, also a derivative of the medial part of the olfactory placode, has led to some interesting speculations, from evolutionary and physiological perspectives, about the origin of these cells and the role of the terminalis nerve in their migration.

Formation of chondrous and osseous tissues in micromass cultures of rat frontonasal and mandibular ectomesenchyme

Rat frontonasal and mandibular mesenchyme was isolated from day-12 1/2 (stage-22) rat embryos and cultured at high density for up to 12 days. The stage chosen was based on the observation that mandibular mesenchyme at this stage became independent of its epithelium with respect to the production of both cartilage and bone. Frontonasal cultures developed aggregates of anastomosing columns of cells within 2 days. These grew as the cells enlarged, laying down an Alcian-blue-positive matrix by day 3 of culture. Significant mineral was detected by von Kossa staining by day 5 at which time the aggregates covered a large portion of the culture, eventually covering the entire micromass by day 10-12. Mandibular cultures developed centrally located nodular aggregates by 3 days of culture. These nodules increased in number, spreading outwards as the cells enlarged, laying down an Alcian-blue-positive matrix by day 4 and mineral by days 6-7. At this time the nodules began to elongate and coalesce, but never covered the entire culture over the 12-day period. Antibody staining revealed that in both cultures the cells were initially positive for type I collagen. Subsequently, the aggregates began expressing type II collagen, followed by type X, which coincided with the onset of mineralization. At this time some cells were negative for these cartilage markers, but positive for osteoblast markers, bone sialoprotein II, osteocalcin and type I collagen. In addition osteonectin and alkaline phosphatase were demonstrable in all of the aggregate cells late in the culture period. This provided clear evidence that chondroblast and osteoblast differentiation was proceeding within these cultures. The culture of rat facial mesenchyme should prove very useful, not only for the analysis of bone and cartilage induction and lineage relationships, but also in furthering our knowledge of craniofacial differentiation, growth and pattern formation by extending our analysis to a mammalian system.

Developmental nasal anomalies

Despite the complex embryological development of the nose and surrounding structures, significant developmental nasal anomalies are rare. We therefore present our experience in the management of such anomalies (excluding choanal atresia) over the past 10 years. Fifty cases were surgically treated; two nasopharyngeal cysts, four hairy polyps, two meningoencephalocoeles, seven gliomata, 20 dermoids, two capillary haemangiomata, four fibromas, one fibromyxyoma, one mucocoele, one granuloma, one lipoma, two nasal aplasias, two nasal clefts and one nasal web. All cases presented with nasal obstruction and/or as a nasal mass. Computerized tomography and magnetic resonance imaging aided diagnosis determining the extent of intracranial involvement. Various surgical techniques were used ranging from simple excision to the lateral rhinotomy and Goodman's external rhinoplasty approach. Only five patients (10 per cent) suffered complications; two CSF leaks and three recurrences, all treated successfully.

Developmental expression of the putative transcription factor Egr-1 suggests that Egr-1 and c-fos are coregulated in some tissues

We have investigated developmental expression of the gene Egr-1, which encodes a protein containing three zinc fingers. Egr-1 like c-fos is a serum inducible, early response gene, which is co-induced with c-fos in a variety of quite different situations. A single 3.7-kb RNA was detected throughout fetal mouse development, which increased in absolute levels in total fetal RNA from 9.5 to 12.5 days post coitum (p.c.). In situ hybridization to 14.5- and 17.5-day p.c. fetal tissues demonstrated Egr-1 accumulation at several specific sites. These included mesenchymal components of the developing tooth germs and salivary and nasal glands; an ectodermally derived component of the whisker pad and developing muscle, cartilage, and bone. Expression of Egr-1 in cartilage and bone showed a strikingly similar expression to previously published reports of c-fos in these tissues. High levels of Egr-1 RNA was observed at the perichondrial interface of opposing cartilaginous elements and in interstitial cells that lie in between. Bone expression was observed in membranous bone of the head, alveolar bone around the tooth germs, and at periosteal and endochondral ossification sites in the limb bones. Our data support the idea that Egr-1 and c-fos may be coregulated in vivo and together may regulate normal development of the skeleton.

Characterization of epithelial domains in the nasal passages of chick embryos: spatial and temporal mapping of a range of extracellular matrix and cell surface molecules during development of the nasal placode

The formation of the nasal passages involves complex morphogenesis and their lining develops a spatially ordered pattern of differentiation, with distinct domains of olfactory and respiratory epithelium. Using antibodies to the neural cell adhesion molecule (N-CAM), keratan sulphate and heparan sulphate proteoglycan (HSPG) and a panel of lectins (agglutinins of Canavalia ensiformis (ConA), Dolichos biflorus (DBA), peanut (PNA), Ricinis communis (RCA1), soybean (SBA), Ulex europaeus (UEA1), and wheatgerm (WGA], we have documented cell surface characteristics of each epithelial domain. Binding of antibodies to N-CAM and to keratan sulphate, and the lectins ConA, PNA, RCA1, SBA and WGA marks the olfactory epithelial domain only. The restriction of N-CAM to the sensory region of the epithelium has also been reported in the developing ear. This striking similarity is consistent with the idea that N-CAM may be involved in the division of functionally and histologically distinct cell groups within an epithelium. We traced the olfactory-specific cell markers during development to gain insights into the origin of the epithelial lining of the nasal passages. All reagents bind at early stages to the thickened nasal placode and surrounding head ectoderm and then become progressively restricted to the olfactory domain. The expression of these characteristics appears to be modulated during development rather than being cell autonomous. The distribution of keratan sulphate was compared with collagen type II in relation to the specification of the chondrocranium. Keratan sulphate and collagen type II are only colocalized at the epithelial-mesenchymal interface during early nasal development. At later stages, only collagen type II is expressed at the interface throughout the nasal passages, whereas keratan sulphate is absent beneath the respiratory epithelium.

A test of two midfacial growth models using path analysis of normal human fetal material

Predictions about the temporal sequencing (i.e., primacy) and causal relationships between various midfacial growth components, as suggested by two midfacial growth models (functional matrix and septal traction), were examined in the present study. The relationships between quantitative changes in the nasal septum, nasal airway, nasolabial musculature, and premaxilla of 15 normal human fetal specimens, ranging in age from 12 to 20 weeks postmenstrual age, were assessed using the multivariate technique of path analysis. Path analysis results revealed that the causal sequence of variables proposed by the septal-traction model explained more of the variance in premaxillary size (87 percent goodness-of-fit) than did the sequence of variables proposed by the functional matrix model (65 percent goodness-of-fit). These results suggest that the septal-traction model may be a more parsimonious and primary explanation of early human fetal midfacial growth than the functional matrix model. Path analysis results also reiterate the observed complex developmental relationships within the fetal labioseptopremaxillary region, knowledge of which may be important in the surgical management of infants with complete cleft.

Topographical projection of the septal organ to the main olfactory bulb in rats: ontogenetic study

Using the horseradish peroxidase (HRP) retrograde tracing method, we have studied the topographical organization of the projection of the septal organ to the main olfactory bulb in rats varying in age from 22 fetal days up to 15 postnatal days. For all developmental stages studied, receptor cells of the septal organ had their axons ending in a relatively circumscribed region of the olfactory bulb, which was the posterior ventromedial bulbar aspect. In younger animals, olfactory receptor cells were observed within the epithelial area isolating the septal organ from the olfactory epithelium, whereas this area was reported to be an exclusive respiratory region in adult rats. The complete disappearance of these receptor cells noted in 12-day-old rats was related to some ontogenetic process.

The importance of embryological research in the surgical management of the cleft lip deformity

The cleft lip deformity has been present throughout mankind, and has entered into the folklore of Nations. There has been a multitude of described repairs. Still they do not provide the hoped for final results. Some of the changes have been based on "thought out" ideas, others on futile guesses. The last few years have seen changes in the surgical direction due to a clearer understanding of the basic embryology. These changes have been made possible by advances in equipment and technology. Changes in animal research, both intra- and extra-uterine, have made possible experiments which may answer some of the suppositions put forward covering both development and healing. The classification of cleft lip places all the deformities in one group, but there may in fact be several groups with different actual causes and failures leading to the same clinical picture. The understanding of the failure or failures that occur in development should lead to a logical approach to the repair of the cleft deformity.