Morphogenesis of Mandibular Dental Arch Shape in Human Embryos

Changes in shape of the mandibular dental arch were demonstrated in a developmentally representative sample of human embryos. Each reconstructed arch was described in terms of a conformance to a reference geometric curve; ie, catenary. Cross-sectional sample trends showed that the initial dental lamina is anteroposteriorly flattened during the sixth week and begins a progressive elongation and conformance to the catenary curve in 8½-week embryos.

Student Assessment of Teaching Effectiveness in a Multi-Instructor Course for Multidisciplinary Health Professional Students

Student evaluations of teaching effectiveness in a large multi-instructor human anatomy course for students from four professionalprograms (nursing, dental hygiene, pharmacy, and physical education) were examined over a three-year period to assess the influence of professional program on student ratings of instruction. In spite of wide differences in mean achievement, students in the four professional groups were relatively consistent in their differential evaluations of the three course instructors and in their evaluations of learner motivational and course performance dimensions of instruction. Results supportedpreviousfindings regarding both (a) the internal consistency and interrater reliability of student evaluations of instruction in a course format increasingly being used in health professional education and (b) the needfor multiple assessments of instruction over time before generalizations can be made about an individual instructor's teaching skill.

Re-Visiting the Embryogenesis of the Human Lower Lip: An Overlooked Paradigm

The rare opportunity to study a human fetus showing bilateral clefting of the lower lip along with other associated anomalies resembling those of the equally rare Pena–Shokeir phenotype prompts this report. The scarcity of reports on bilateral clefts of the lower lip has strengthened the conventional understanding or, perhaps even dogma that the lower lip and jaw develop from the progressive midline merging of just two mandibular prominences in the embryo. On the basis of observations stemming from this case report, it is proposed that yet another developmental event or process (in addition to the midline merging of the mandibular prominences) may be operable in the normal morphogenesis of the lower lip and anterior mandibular region. The bilateral paramedian clefting observed provides evidence that another distinct developmental region, a small medial process complements mandibular morphogenesis.

Patterns of body and visceral growth in human prenates with clefts of the lip and palate

OBJECTIVE

To address the hypothesis that human prenates with birth defects such as clefts of the lip and palate show growth patterns in which body size and visceral growth are aberrant for prenatal age.

METHODS

Body size and organ weight measurements were derived from a cross-sectional population sample of 167 legally donated human embryos that were representative of key periods in visceral organogenesis and growth. Measurements included those of overall body size (i.e., length and weight) and weights of major organs. Data were analyzed for two comparative (age-matched) groups consisting of 120 typical-for-age "control" and 47 specimens showing the three typical cleft types. Organ weight data for the entire cleft group and for each of the three cleft subgroups were compared with those of the control group.

RESULTS

Cleft specimens showed crown-rump body sizes that were within one standard deviation of the control group. Among the entire cleft sample, each of the organ weight values was generally consistent with the organ weights observed for the age-matched control group. When organ weights for the cleft group differed from the controls, with one exception, some organs showed either increased or decreased organ weights. One remarkable exception was with lung weights, which were reduced for each of the prenates across the three cleft types. Among the three cleft groups, fetuses with cleft lip and palate showed the highest percentage of organ weight discrepancies (i.e., smaller than expected) as compared with the group with cleft palate, which showed the lowest. CONCLUSIONS; Organ weight aberrancies were observable (whether increased or reduced weights), and such aberrancies were not apparent until approximately 24 weeks (fertilization age).

Postnatal presence of paraseptal cartilages in humans: a description of morphology and size

Paraseptal cartilages (PCs) have been the subject of controversy, in that some authors believe them to be absent or rarely present, while others have described them to exist at predictable locations in adult human tissue specimens. This study seeks to determine the presence or absence of PCs in humans and describe their morphology and size. Nasal septal tissue from 19 adults and 1 child were paraffin embedded, coronally sectioned, placed on slides, and stained for microscopic observation. For all specimens, PCs were identified and lengths were calculated. Selected PCs were also digitized in order to calculate volume. Results demonstrated that PCs were present in all 20 tissue specimens and assumed a common morphology. In each, PCs were found to begin as hyaline cartilage lobes that extend projections in a superolateral direction as an anteroposterior course is followed. The projections were found to rotate inferiorly until each PC was found to assume a position that extended below the nasal septum. Length measures in adults ranged from 8,725 to 19,000 microm (x = 14,188.9 microm) and volumes ranged from 7.7 to 24.2 (x = 13.2) x 10(-3) ml. A quantitative comparison to foetal data from a previous study suggests prenatal and/or postnatal growth of PCs. Results from this study support the presence of PCs in adult humans as well as prenatal/postnatal growth of PCs.

Searching for the vomeronasal organ of adult humans: preliminary findings on location, structure, and size

The adult human vomeronasal organ (VNO) has been the focus of numerous recent investigations, yet its developmental continuity from the human fetal VNO is poorly understood. The present study compared new data on the adult human "VNO" with previous findings on the fetal human VNO. Nasal septa were removed from twelve adult human cadavers and each specimen was histologically sectioned. Coronal sections were stained with hematoxylin-eosin and periodic acid-Schiff-hematoxylin. The sections were examined by light microscopy for the presence of VNOs and the anterior paraseptal cartilages (PC). VNOs were quantified using a computer reconstruction technique to obtain VNO length, volume, and vomeronasal epithelium (VNE) volume. Histologically, VNOs and PCs were identified in eleven specimens. VNOs had ciliated, pseudostratified columnar epithelium with goblet cells. Variations (e.g., multiple communications to the nasal cavity) were observed in several specimens. Quantification was possible for 16 right or left VNOs. Right or left VNOs ranged from 3.5 to 11.8 mm in length, from 1.8 to 33.8 x 10(-4)cc in volume, and from 2.7 to 18.1 x 10(-4)cc in VNE volume. Results indicated that the adult human VNO was similar in VNE morphology, lumen shape, and spatial relationships when compared to human fetal VNOs. By comparison with previous fetal VNO measures, mean VNO length, volume, and VNE volume were larger in adult humans. These results support previous suggestions that postnatal VNO growth occurs. Findings on location and spatial relationships of the adult VNO were similar to those seen in human fetuses, but critical questions remain regarding the ontogeny of the vomeronasal nerves and VNE.

Prenatal fluoride for growth and development: Part X

Examinations of prenatal fluoride supplemented (PNF) teeth in an animal model and in a five-month human fetus find these teeth to be more developed than the non-supplemented controls. The fact that PNF allows teeth to develop to their full potential suggests that PNF could be an essential nutrient for the entire human and this could be demonstrated most easily during rapid fetal growth. A review of the recent literature, including trials by NIH and The World Health Organization, provide evidence that fluoride (F) does allow the fetus to grow and develop to its full potential. The authors conclude that PNF must be supplied in at least a 2 mg/day pulse dose, and then F must be given from shortly after birth in a daily amount appropriate for the weight of the child with some consideration for the amount of F water utilized.

Prenatal growth of the human vomeronasal organ

BACKGROUND

Vomeronasal organs (VNOs) are paired epithelial structures located adjacent to the nasal septum that form in the late first trimester of human fetal development. Although VNOs have long been known to exist in fetal and adult humans, some studies continue to suggest that these structures may be degenerative or functionless. Little is known of the growth of the VNO.

METHODS

The present study examined length and volume changes of the human VNO in 26 "normal" (10 female, 16 male) histologically prepared fetuses from the University of Pittsburgh and the University of Michigan across three trimesters (8-30 weeks postmenstrual age). A computer reconstruction technique was used to quantify lengths and volumes of right and left VNOs, and regression equations were generated to assess growth rates.

RESULTS

A linear increase in VNO length and a logarithmic increase in VNO volume with increasing postmenstrual age was found. Volume increase was noted for both the vomeronasal epithelium and the lumen of the VNO. A comparison with most estimates of adult human VNO length suggested that further prenatal or postnatal size increase occurs. The growth curves also suggested a more rapid growth in VNO length and volume for females than for males.

CONCLUSIONS

The present study demonstrates that the fetal human VNO commences volumetric increase in the early second trimester but does not achieve maximum size during fetal development. Further investigation is needed to determine whether the human VNO is sexually dimorphic in size.

Vomeronasal organ growth and development in normal and cleft lip and palate human fetuses

As part of an ongoing investigation of normal and cleft lip and palate (CLP) fetal midfacial development, the vomeronasal organ (VNO) was examined in 35 human fetuses (26 normal and 9 CLP) ranging in age from 8 to 30 weeks postmenstrual age. All specimens were examined histologically, and a computer reconstruction technique was used to quantify lengths and volumes of right and left VNOs and anterior paraseptal cartilages (PCs). Growth curves were generated for these data and were compared between normal and cleft samples. VNOs and PCs were present in all normal fetuses, whereas VNOs were found in only 5 of 9 CLP specimens and PCs were found in 8 CLP specimens. The side of the palatal cleft in specimens with unilateral CLP was associated with PC dysmorphologies but appeared to have no influence on VNO presence or absence. Septal dysmorphologies were observed in most CLP specimens with absent or abnormal VNOs. VNO length increased in a linear fashion across ages, and VNO volume was seen to change in a logarithmic fashion. Individual CLP specimens did not differ significantly from the mean of the normal sample for VNO length or volume. PC length was seen to change in a sigmoidal fashion, and PC volume changes were best described by a logarithmic curve. In contrast to findings on the VNO, CLP specimens exhibited significantly different growth rates (line slopes) for PC length and volume compared to the normal sample. Results on the normal sample suggested that the human fetal VNO exhibits volumetric increases between the 16th and 30th weeks of development, but this increase begins later and proceeds more slowly than that of the PCs. Examination of the CLP sample suggested that the VNOs were of "normal" size for age, but may be vulnerable to septal dysmorphologies that result in altered location or disruption.

Histomorphologic analysis of the soft palate musculature in prenatal cleft and noncleft A/Jax mice

The two specific aims of this study were as follows: to evaluate the appropriateness of the A/Jax mouse model in the investigation of the key cellular stages in prenatal soft palate morphogenesis and myogenesis; and to describe structural differences in the histomorphology of the soft palate anatomy from cleft and noncleft mice prior to, during, and after palatogenesis. Cleft-induced and control groups of A/Jax mouse embryos from timed pregnancies were harvested sequentially on gestational days 15 to 19. Embryos were weighed and staged for external body morphology. The heads were removed and fixed for light microscopy, sectioned serially in the frontal plane at 10 microns and stained with hematoxylin-eosin to characterize and compare the soft palate musculature. All observations were made at the head depth of the trigeminal ganglion in both age- and stage-matched embryos. The following findings were made: (1) the A/Jax mouse is a suitable animal model for the study of soft palate myogenesis; (2) there were no discernible morphologic differences between the soft palate muscles in cleft and noncleft A/Jax mice when viewed under light microscopy; (3) the soft palate and related muscles were identifiable as muscle fields, in both the cleft and noncleft fetuses, as early as gestational day 15 and as specific muscles at gestational day 18; (4) in both the cleft and noncleft A/Jax fetuses, the soft palate muscles appeared in a sequential anatomic fashion (the palatine aponeurosis appeared first, next the tensor palatini, and then the levator palatini muscles); and (5) in the cleft palate fetuses, both pterygoid plates were angulated and displaced laterally.

Patterns of abnormal myogenesis in human cleft palates

To test the hypothesis that soft palate muscles are abnormal in cleft palate, we compared soft palate morphogenesis in fetuses with cleft palate (n = 4) to age-matched (n = 3) and nonmatched (n = 1) control specimens. The morphologic status of all soft palate and masticatory structures were classified into one of six stages based on the level of histogenesis. At 54 mm crown-rump length (CRL), the levator veli palatini (L), palatopharyngeus (PP), and palatoglossus (PG) in cleft subjects demonstrated mesenchymal condensation into myoblastic fields, lagging behind the control specimens (97 mm CRL), which displayed definitive fields of myoblasts and myotube formation. In the 175 mm and 225 mm cleft and the 170 mm and 192 mm control specimens, muscular morphology was similar and had reached its postnatal appearance for the tensor veli palatini (175 m only) and L, PP, PG (225 mm only). Muscle fiber directions were, however, disoriented and disorganized, especially close to the medial epithelial edge of the cleft. The levator veli palatini, could not be distinguished as a discrete muscle in the cleft specimens, and what we believed to be the PP and PG seemed "normal" at the level of light microscopy, but malpositioned in a superior direction. This preliminary study demonstrates for the first time that early myogenesis in cleft palates differs from normal.

Soft-palate myogenesis: a developmental field paradigm

Surgical correction of clefts of the soft palate leads to varying degrees of normal function although the repair itself is successful. Explanations for this include structural abnormalities of the muscles. Previous studies have focused primarily on gross anatomical features of late fetal and postnatal cleft palate musculature; however, infrequent reference has been made to early prenatal morphologic patterns of soft-palate development, beginning with the embryo. Thus we evaluated the chronology of prenatal myogenesis of the soft palate from its early mesenchymal phase through the appearance of definitive palatal muscles and associated structures in a sample of 22 human fetuses that represented postfertilization weeks 6.5 to 20.5 (18- to 192-mm crown-rump length). Specimens were histologically prepared for descriptive and morphometric light microscopy. Data were collected on the earliest appearance times of identifiable soft palate and associated structures within the mesenchymal field and on their individual stages of myogenesis (e.g., for muscles, from mesenchyme to myoblasts to fascicles). Analyses showed that (1) palatal muscles and related bony structures emerge sequentially as densely staining mesenchymal subfields within the larger mesenchymal soft-palate field during the 6- to 9-week period, with the tensor veli palatini muscle appearing earliest, and the musculus uvulae latest; (2) further morphogenesis of the soft palate and associated structures follows a definite timeline; and (3) by 16 to 17 weeks the postnatal palatal morphology is in place.

Patterns of Abnormal Myogenesis in Human Cleft Palates

To test the hypothesis that soft palate muscles are abnormal in cleft palate, we compared soft palate morphogenesis in fetuses with cleft palate (n=4) to age-matched (n=3) and nonmatched (n=1) control specimens. The morphologic status of all soft palate and masticatory structures were classified into one of six stages based on the level of histogenesis. At 54 mm crown-rump length (CRL), the levator vell palatini (L), palatopharyngeus (PP), and palatoglossus (PG) in cleft subjects demonstrated mesenchymal condensation into myoblastic fields, lagging behind the control specimens (97 mm CRL), which displayed definitive fields of myoblasts and myotube formation. In the 175 mm and 225 mm cleft and the 170 mm and 192 mm control specimens, muscular morphology was similar and had reached its postnatal appearance for the tensor veli palatini (175 m only) and L, PP, PG (225 mm only). Muscle fiber directions were, however, disoriented and disorganized, especially close to the medial epithelial edge of the cleft. The levator veli palatini, could not be distinguished as a discrete muscle in the cleft specimens, and what we believed to be the PP and PG seemed “normal” at the level of light microscopy, but malpositioned in a superior direction. This preliminary study demonstrates for the first time that early myogenesis in cleft palates differs from normal.

Prenatal pattern emergence in early human facial development

This report addresses the emergence of proportional patterns in the early development of the human face. Fifty-nine human embryos and fetuses (7 through 26 weeks fertilization age) constituted a "normal" study sample. Midfacial cephalometric analyses were done on projected histologic sections cut frontally through the maxillary deciduous first molar tooth crowns. The midface was divided into three cephalometric zones. Data show that while each zone increases in absolute width, least change is seen in the central facial zone, with greatest change seen in the lateral-most facial zone. This pattern of proportional stability of the central facial zone becomes evident at 9 weeks gestation, at which time the changing embryonic optical axes have converged toward the midline to within several degrees of their position at birth. These data show that the central portion of the postnatal facial T-zone has a clearly recognizable prenatal antecedent as early as the ninth week in fetal life.

Critical periods in the prenatal morphogenesis of the human lateral pterygoid muscle, the mandibular condyle, the articular disk, and medial articular capsule

This study was prompted by the renewed clinical interests in understanding the natural history or early morphogenesis of the human temporomandibular joint. Using histologic preparations of 52 representative human embryos and fetuses, each of the major components of the joint was systematically assessed for its changing structure and related to an approximate time scale. The emergence and continued morphogenesis of the joint articular fossa, mandibular condyle, disk, capsule, lateral pterygoid muscle fibers, and both joint cavities occur in regular temporal and spatial pattern. A key observation from this study of embryos and fetuses ranging in age from 32 days to 22 weeks is that each of the component parts of the TMJ progressively emerge with some kind of continuity from a common mass of embryonic mesenchyme interposed between the future temporal bone and mandibular regions. The observations of this study lead to the suggestion that significant developmental disturbances to this common tissue mass or "developmental field" can lead to anomalous morphogenesis of those structures expected to emerge over time from the "developmental field" of the temporomandibular joint. Timing and the identification of a critical time period for the joint are important variables. This study identifies the critical period in the early morphogenesis of TMJ structures as generally falling between the early 7th and 11th prenatal weeks.

The natural history and pathogenesis of the cranial coronal ring articulations: implications in understanding the pathogenesis of the Crouzon craniostenotic defects

The craniostenotic birth defects seen in patients with Crouzon syndrome have prompted this developmental study on the system of articulations between the human frontal, sphenoid, and ethmoid bones. The Crouzon facies, including midfacial hypoplasia and exorbitism, have been linked to the premature synostosis of calvarial sutures. However, considerable evidence shows that midfacial positioning is linked to increasing length of the midline cranial base. Thirty-seven typical-for-age (8 to 29 weeks) embryos were histologically prepared, read serially, and three-dimensionally reconstructed to map the so-called coronal ring articulations that continuously join the frontal, sphenoid, and ethmoid bones. A morphologic staging plan was used to show the progressive development of bones and intervening joints. Data show that a coronal ring exists beginning at 8 weeks. Those portions of the ring separating the frontal and sphenoid bones (within the orbit and laterally along the coronal suture) show the typical structure of a five-layered suture. This sutural component of the ring is C-shaped with a cartilaginous bridge between the optic foramina completing the ring. This is the sphenoethmoidal (S-E) synchondrosis of the midline cranial base. It is suggested that this deeply located cartilage joint is the primary site of pathogenesis in the craniostenotic facies and not the coronal sutures which are operated upon. Even though the S-E cartilage would be difficult and potentially morbid to approach surgically, this study would suggest that preoperative computed tomography (CT) of the skull base with special emphasis on the S-E region may provide a better prognosis regarding midface growth effects after surgery. It appears to be the fused S-E synchondrosis and not necessarily the premature closure of the coronal sutures that may tether the midface posteriorly.

Congenital hemifacial hyperplasia: an embryologic hypothesis and case report

Congenital hyperplasia is a developmental disorder characterized by marked unilateral asymmetry. The structural disproportions from one side to the other far exceed variations commonly seen in the normal population. Classically, as first described in 1836, the overgrowth of tissue is restricted to one-half of the body, including the extremities. In other cases the hyperplastic enlargement involves segmental areas of the body, such as the hemifacial skeleton and an extremity. A case report is presented, and the clinical characteristics of 192 cases of congenital hyperplasia in the literature are briefly reviewed. Use of the word hyperplasia to describe the condition (rather than hypertrophy) is encouraged. The authors propose a new embryologic hypothesis: asymmetrical development of the neural fold and hyperplasia of the neural crest cells are said to form the basis for the disorder. The rewards, risks, and limitations of reconstructive surgery over a 10-year period are discussed.

Reexamination of the origin and early development of the human larynx

The respiratory primordium buds off the primitive foregut and grows caudally, on a lengthening stalk; the cephalic end of the stalk develops into the glottis and infraglottis, and the rest becomes the trachea. Compression by pharyngeal mesoderm cephalic to the respiratory diverticulum obliterates the foregut lumen ventrodorsally as far cranially as the 4th pharyngeal pouches, forming an epithelial lamina with a narrow pharyngoglottic duct along its dorsal border. The mesoderm also raises an epiglottic and two arytenoid swellings in the pharyngeal floor at the level of the 4th pouches; the triangular 'cecum', bounded by these swellings, grows caudally along the ventral border of the epithelial lamina to just above the glottis. Beginning at stage 21, the epithelial lamina separates cephalocaudally, bringing the cecal lumen into continuity with the pharyngoglottic duct to form the laryngeal vestibule; when the separation is complete, the vestibule is continuous with the infraglottic cavity. Meanwhile, bilateral pouches arising from the caudal end of the cecum form the ventricles, the lower lips of which become the vocal folds, and the pharyngeal mesoderm surrounding the laryngeal cavity gives rise to the laryngeal cartilages and intrinsic musculature. The cricoid chondrifies bilaterally from a single center in the ventral arch of a precartilaginous template that encircles the infraglottic cavity, and on meeting forms the dorsal lamina. Each arytenoid chondrifies from a single center, and each half of the thyroid cartilage chondrifies from two. Anlagen for the intrinsic muscles appear during stage 17, sites of individual muscles are recognizable by stage 23, and myofibrils are present by the 12th week.

Adipose tissue growth patterns during human gestation: a histometric comparison of buccal and gluteal fat depots

Morphometric analysis of fat lobule size and number, and fat cell number in middle buccal and gluteal fat depots during the prenatal period was carried out using histological sections from 88 typical-for-age or normal human prenates of both sexes. The sample ranged from 110 to 385 mm Crown-Rump length (or from 14 through 42 gestational weeks). Compared with the buccal fat pad, the gluteal fat was one to four weeks delayed in lobule maturation. In addition to fat maturation differences between buccal and gluteal fat sites, gluteal fat characteristically showed fewer but larger fat lobules than did the buccal fat pad. Conversely there appeared a larger number of fat cells per unit area in the buccal fat than in the gluteal fat. Fat accumulation in human buccal and gluteal fat depots include differences in growth timing and magnitude, but also different developmental patterns. These patterns suggests our hypothesis that while lobule hyperplasia and hypertrophy occur at both sites, gluteal fat lobules grow primarily through lobule hypertrophy whereas the buccal fetal pad grows through lobule hyperplasia.

Crown area as an indicator of changing crown size in human pre-natal teeth

This study deals with correlations of tooth size in human primary teeth. Traditionally, mesiodistal or buccolingual measurements have been used to express crown size. However, in this study, crown area was used as a reference parameter. Graphic reconstructions of 38 histologically prepared human fetuses with Crown-Rump Length (CRL) between 54 and 280 mm were used to obtain linear and area measurements. Based on clinical records and physical examinations, these fetuses were considered typical-for-age, or "normal". Correlation matrices indicated high levels of concordance among all developing deciduous tooth crowns and arch measurements. It was concluded that crown area is a statistically better trait to use in comparison of teeth rather than the traditional mesiodistal measurement.

The chronology of adipose tissue appearance and distribution in the human fetus

Timing of first appearance and subsequent distribution of adipose tissue were assessed in 488 normal-for-age human fetuses. The sample represented each of the three trimesters of normal pregnancies. Light microscopy showed that adipose tissue first appears and progressively develops from the 14th to 24th week of gestation (100-216 mm crown-rump length) in those areas where it characteristically accumulates after birth. No significant sex differences were found in patterns of early fat deposition. It is suggested that the second trimester of gestation is the critical or key period in fat adipogenesis.

Growth and development of human adipose tissue during early gestation

805 normal-for-age human embryos and fetuses were used to study early prenatal fat development. The investigation included observations on stages of fat morphogenesis at the light microscopic level and computerized image analyses of fat lobule size and number. The buccal fat pad was selected as a model system for the analyses. Fat tissue differentiates between the 14th and the 16th weeks: there are five morphogenic phases in adipose tissue formation, strongly associated with the formation of blood vessels. Fat lobules are the earliest structures to be identified before typical vacuolated fat cells appear. Concerning fat lobule size and number, we show that after the 23rd week the total number of fat lobules remains approximately constant, while from the 23rd to 29th week the growth of adipose tissue is determined mainly by an increase in size of the lobules. These results suggest that the 14th through the 23rd week is a sensitive period in fat lobule development, and that disturbances of normal adipogenesis during this period may play a role in the etiology of obesity in later life.

Congenital alar field defects: clinical and embryological observations

Congenital malformations of the nasal ala may occur as isolated unilateral nasal alar defects or as part of more severe facial clefting syndromes. The embryologic significance of the isolated alar deformity seems separate from other craniofacial deformities and justified comment. Clinical examples of isolated nasal alar malformations are correlated with a study of 60 human embryos ranging from seven to 10 weeks gestation. These studies indicate that the nasal and alar developmental fields each have a separate critical time during which cells are most susceptible to altered development.

Comment on the prune belly syndrome: a 11-week fetus with megacystis

An 11-week human fetus with megacystis, prostatic dysgenesis, and lateral displacement of the abdominal muscles is described. We suggest that a subtle outflow obstruction of the very early bladder may give rise to both bladder dilation and bladder wall dysgenesis. The bladder dilation may produce abdominal muscle dysplasia or atrophy and almost certainly produces dilation of the prostatic urethra. The dilation of the prostatic urethra disrupts the formation of the prostate.

Adjacency effects in developmental correlations among tooth organs in human fetuses

This study explores whether the "distance gradient" model shown for embryonic development and postnatal tooth growth is also characteristic of the fetal period. Histologic data and ratings from 26 human fetuses show that, unlike the embryonic and postnatal periods, changes occurring in two tooth germs are significantly alike, regardless of the number of intervening teeth.

Crown size-arch space relationships during human prenatal dental development

As shown in composite reconstructions made from optically-projected measurements of 10mu frontal maxillofacial sections of 20 histologically normal fetuses and embryos in the 70-255 mm CRL range, individual differences in relative tooth size and interdental spacing are evident by 10.5-11 weeks of gestation, and age-corrected crown-size correlations (r=0.40) approximate those in postnatal life. Despite an eight-fold increase in crown dimensions, interdental spacing remains approximately constant after 150 mm CRL, suggesting that the tooth organs or the periodontal membranes are able to maintain spacing, into the third trimester.

Prenatal growth patterns of the human mandible and masseter muscle complex

Since experimental and clinical evidence supports some role of musculature in determining the form and size of facial bones during the active periods of growth after birth, this study addresses the same basic relationships between muscle and bone during the periods of active growth before birth. The relationship between the masseter muscle and the mandible, including its ramal and body components, was chosen as the model for study in nineteen human fetuses (ages 16 to 36 weeks). Cross-sectional cephalometric data indicated that, although increases in the size of the muscle and mandible were linearly related to increasing age, the ramal portion of the mandible was more closely related to changes in the masseter muscle than to changes in the mandibular body. Moreover, it appears that reorientation of the muscle anteriorly and downward precedes a similar reorientation of the ramus, with the combination of both fetal events leading to the typical relationships of the two structures expected after birth. Although this study does not get to cause-and-effect relationships, and although the fetal specimens cannot be monitored longitudinally over time, the parallelisms between our prenatal findings and those reported for postnatal periods certainly lend further support to the observation that many aspects of morphogenesis and growth are continual processes spanning the periods on either side of birth.

Congenital bipartite scaphoid--fact or fiction?

Whether there is such a condition as congenital bipartite scaphoid has long been debated. Five cases that fulfill the established criteria are presented, supplemented by a review of roentgenograms of 17,439 hands in which no case of bipartite scaphoid was detected. Serial sections of 196 fetal hands also failed to reveal any evidence of bipartite development of the scaphoid. We concluded that bipartite scaphoid is of traumatic origin and should be treated accordingly.

Warfarin-associated embryopathy in a 17-week-old abortus

Histological and anthropometric studies were made of the hands and face of a 17-week-old (postmenstrual) human fetus that was exposed to warfarin throughout gestation. The fetus had marked nasal hypoplasia and the facial cartilages contained discrete foci of abnormal cartilage. When compared with age-matched control fetuses hand pattern profile analysis showed that the brachydactyly was due to shortening of the terminal phalanges. Histologically chondrogenesis was disordered in the carpals and phalanges, with the most deviant development occurring at the distal ends of the terminal phalanges. In none of the areas of abnormal cartilage was there evidence of hemorrhage or hemosiderin deposition. It is our contention that warfarin is teratogenic in human beings and that its teratogenicity is not due to focal hemorrhage.

Prenatal origins of carpal fusions

As shown in 138 embryos and fetuses in the 40-285 mm crown-rump length range, carpal and carpal-metacarpal "fusions" arise from incomplete separation of the cartilaginous precursors rather than from failure of initiation, thus accounting for the "fusions" seen in postnatal radiographs and the grooves that are evident enough in adult fusions. Radiographs selected from over 20,000 apparently normal individuals provide postnatal counterparts for the prenatal examples shown in histological sections.

Prenatal origin of brachymesophalangia-5

As shown in 91 embryos and fetuses in the 41-235 mm crownrump length, brachymesophalangia-5 may be identified in prenatal time. Although the ratios involving different combinations of length of mid-5 relative to other segments yield different frequencies of BMP-5, the short middle segment of the little finger is already associated with clinodactyly and developmental eccentricity as early as the ninth week of prenatal development.

Early prenatal attainment of adult metacarpal-phalangeal rankings and proportions

As shown in 56 human embryos and fetuses between 15 and 104 mm in crown-rump length, "adult" metacarpal-phalangeal length rankings are attained by the seventh intrauterine week and near-adult bone-to-bone ratios or proportions by the theirteenth week. Micrometric measurements of optically-projected histological hand sections show relative elongation of the distals between the 15-29 mm and 30-44 mm crown-rump range, and relative reduction to radiogrammetrically-determined adult proportions by the 90-104 mm CRL.

Mandibular precedence in the prenatal development of four permanent teeth

As shown in 62 pairs of dental opponents from 32 grossly normal human fetuses in the 75-378 mm crown-rump range, mandibular precedence is the rule for 11, 12, C and M1, a trend in agreement with mandibular precedence for deciduous teeth through dm1 and in the gingival emergence of the same permanent teeth during postnatal development.

Spontaneous pleural effusion in a human fetus

Left sided pleural effusion was found in a human fetus spontaneously aborted at 20 weeks postmenstrual. Pulmonary hypoplasia associated with the effusion suggested that the fluid had been present for some time before delivery. Absence of other anomalies supports the view that the effusion was due to maldevelopment of the thoracic lymph channels.