Formation Of Crests Research Articles

Preterm rabbit-derived Precision Cut Lung Slices as alternative model of bronchopulmonary dysplasia in preclinical study: a morphological fine-tuning approach

Bronchopulmonary dysplasia (BPD) is the most common complication of preterm delivery, with significant morbidity and mortality in a neonatal intensive care setting. Research in this field aims to identify the mechanisms of late lung development with possible therapeutic targets and the improvement of medical management. Rabbits represent a suitable lab preclinical tool for mimicking the clinical BPD phenotype. Rabbits are born at term in the alveolar phase as occurs in large animals and humans and in addition, they can be delivered prematurely in contrast to mice and rats. Continuous exposure to high oxygen concentration (95% O2) for 7 days induces functional and morphological lung changes in preterm rabbits that resemble those observed in BPD-affected babies. The preclinical research pays great attention to optimize the experimental procedures, reduce the number of animals used in experiments and, where possible, replace animal models with alternative assays, following the principle of the 3 Rs (Replace, Reduce and Refine). The use of in vitro assays based on the ex vivo culture of Precision Cut Lung Slices (PCLS) goes in this direction, representing a good compromise between controlled and flexible in vitro models and the more physiologically relevant in vivo ones. This work aims to set up morphological analyses to be applied in preclinical tests using preterm rabbits derived PCLS, cultured up to 7 days in different oxygen conditions, as a model. After a preliminary optimization of both lung preparation and histological processing methods of the lung slices of 300 µm, the morphological analysis was conducted evaluating a series of histomorphometric parameters derived from those widely used to follow the phases of lung development and its alterations in vivo. Our histomorphometric results demonstrated that the greatest differences from pseudo-normoxia and hyperoxia exposed samples at day 0, used as starting points to compare changes due to treatments and time, are detectable after 4 days of in vitro culture, representing the most suitable time point for analysis in preclinical screening. The combination of parameters suitable for evaluating PCLS morphology in vitro resulted to be Tissue Density and Septal Thickness. Shape Factor and Roughness, evaluated to highlight the increasing complexity of the airspaces, due to the formation of septal crests, gave useful information, however, without significant differences up to day 4. Other parameters like Mean Linear Intercept and Septal Density did not allow to highlight significant differences between different oxygen conditions and time points. Instead, Radial Alveolar Count, could not be applied to PCLS, due to the tissue changes following agar infusion and culture conditions.

Protection of planting of potatoes from segetal vegetation

Goal. To investigate measures of limiting the number of weeds in planting potatoes on the yield of culture.
 Methods. Field, comparative and analytical.
 Results. The data of technical and economic efficiency of application in landings of potatoes of soil and insurance herbicides, as well as their mixtures are given. It was established that the application after formation of the crests of soil herbicide Zenkor Likvid SC in the normal rate of 1.1 l/ ha provided technical efficiency in 30 days at 77.8%, but did not provide full protection of planting of potato from cereal weeds. Spraying to seedlings with herbicide Zenkor Liquid SC normally consumes 1.1 l/ha and the introduction of Panther antimicrobial herbicide during the period of vegetation, the normally consumes 2.0 l / hectares provided technical efficiency in 30 days at 88.9%. Application in the growing season of the herbicide mixture culture Zenkor Liquid SC + Titus 25, WG in the norms of consumption of 0.2 l/ha + 30 g/ha + surfactant Trend 90, 200 ml / hectare provided technical efficiency at the level of 94.4% for the height of plants of culture 5—10 cm, and at for plant height 10—15 cm — 86.1%. Technical efficiency of the herbicide Titus 25, WG Normally, the consumption of 50 g/ha + surfactant Trend 90, 200 ml/ha was 88.9%, 30 days after spraying, and manual gutting — 80.6%. In variants with application of herbicides yield of potatoes at the level of 18.4—22.0 t/ ha was obtained, in the manual with manual propelling — 18.6 t/ ha, with a yield of 11.2 t/ha.
 Conclusions. To reduce segetal vegetation in potato positions and obtain high yields of tubers it is expedient to spray with soil herbicide Zenkor Liquid SC after the formation of crests to the seedlings of the culture and weeds, the COP normally consumes 1.1 l/ha (metrubuzin, 600 g/l) and in Period of vegetation with herbicide against cereal weeds. During the growing season of potatoes, at a height of culture of 5—10 cm, when weed plants are in the initial stages of growth, landing is sprayed with a mixture of soil and insurance herbicide Zenkor Liquid SC + Titus 25, WG in reduced rates of spending.

Variability of the African equatorial ionization anomaly (EIA) crests during the year 2013

This paper discusses the variability of the position and magnitude of the crests of African Equatorial Ionization Anomaly during noon and post sunset periods. Total electron content data covered the year 2013, and were obtained from a chain of global positioning system receivers in both hemispheres around 37°E longitude. Local magnetometer data were used to infer the direction and magnitude of the E × B drift, while the solar extreme ultraviolet proxy index was used as a measure of solar activity. It was found that the time of formation of both crests varied from 1400 to 1700 local time. Additionally, the position of the crests was found to be asymmetric with respect to the magnetic equator. During the noon period, the position of the northern and southern crests varied from 4.91° to 7.36° and −9.17° to −12.62°, respectively. During the post-sunset period, it varied from 8° to 11.7° and −9° to −16°, respectively. Seasonally, with reference to the magnetic equator, both crests moved poleward during equinoxes and collapsed towards the equator during winter and summer. Equinoxes recorded the greatest crest magnitude followed by winter then summer over both hemispheres during the noon period. However, this trend persisted over the northern crest only during the post-sunset period. Overall, during the noon period, we recorded correlation coefficients of 0.67 and 0.68 between crest magnitudes and ΔH, a proxy for equatorial electrojet current, and 0.88 and 0.81 between crest positions and ΔH, for the northern and southern crests, respectively. During the Halloween day storm of 30 October 2013, a westward electric field inhibited the development of the post-sunset crests.

UV induced surface modification on improving the cytocompatibility of metallocene polyethylene.

Demand for medical implants is rising day by day as the world becomes the place for more diseased and older people. Accordingly, in this research, metallocene polyethylene (mPE), a commonly used polymer was treated with UV rays for improving its biocompatibility. Scanning electron microscopy (SEM) images confirmed the formation of crests and troughs, which depicts the improvement of surface roughness of mPE substrates caused by UV etching. Accordingly, the contact angle measurements revealed that the wettability of mPE-2.5 J/cm2 (68.09º) and mPE-5 J/cm2 (57.93º) samples were found to be increased compared to untreated mPE (86.84º) indicating better hydrophilicity. Further, the UV treated surface exhibited enhanced blood compatibility as determined in APTT (untreated mPE- 55.3 ± 2.5 s, mPE-2.5 J/cm2 - 76.7 ± 4.1 s and mPE-5 J/cm2 - 112.3 ± 2 s) and PT (untreated mPE - 24.7 ± 1.5 s, mPE- 2.5 J/cm2 - 34.3 ± 1.1 s and mPE-5 J/cm2 - 43 ± 2 s) assay. Moreover, the treated mPE-2.5 J/cm2 (4.88%) and mPE-5 J/cm2 (1.79%) showed decreased hemolytic percentage compared to untreated mPE (15.40%) indicating better safety to red blood cells. Interestingly, the changes in physicochemical properties of mPE are directly proportional to the dosage of the UV rays. UV modified mPE surfaces were found to be more compatible as identified through MTT assay, photomicrograph and SEM images of the seeded 3T3 cell population. Hence UV-modified surface of mPE may be successfully exploited for medical implants.

Latitudinal effect on the diurnal variation of the F2 layer at low solar activity

The latitudinal effect on the diurnal variation of the F2 layer peak parameters at low solar activity was investigated. Our results reveal that the likelihood of the occurrence of a noon-bite out is reduced with increase in latitude. Beyond 21.770°N geomagnetic latitude, it is hardly noticed. Daytime maximum NmF2 peak occurs mostly after midday in the northern hemisphere. Similar variations occur in the southern hemisphere, although it varies with the seasons, and latitudes. The maximum ionization decreases with increase in latitude and NmF2 values during the equinoxes are higher than those of the solstice seasons, in the northern hemisphere. It is entirely different in the southern hemisphere. The rate of decay is faster during the solstice than during the equinoxes. Maximum hmF2 values occur at the equatorial ionosphere; the least is in the mid-latitude region. The time of formation and position of the EIA crests is observed to be asymmetric. It appears to be more consistent in the northern hemisphere than the south. These types of seasonal variations have been attributed to the daytime meridional wind, equatorial fountain effect and the location of the subsolar point in relation to the magnetic equator.

Delay in rat lung alveolarization after the combined exposure of maternal hyperglycemia and postnatal hyperoxia

Maternal diabetes interferes with fetal lung development and postnatal treatments may further disturb pulmonary growth. Therefore, we investigated the effect of postnatal oxygen exposure on alveolar development in neonatal rat lungs pre-exposed to intrauterine hyperglycemia. Diabetes was induced in Sprague-Dawley rats with streptozotocin injection before pregnancy. Hyperglycemia-exposed and control litters were randomized to breath room air or 85% oxygen for 7 days after birth. Lungs were analyzed on postnatal d7 for weight, morphology, apoptosis, proliferation, and biomarkers of oxidative stress. Maternal hyperglycemia accelerated lung development as demonstrated by thinner alveolar walls and slightly increased secondary septation when compared to room air bred rats. Hyperoxia alone caused thin-walled and enlarged alveoli with few secondary septa. Interestingly, the dual exposure inhibited the thinning of alveolar walls and the disappearance of mesenchymal cells from the alveolar walls together with the delay in the formation of alveoli and secondary crests. While the lungs' oxidative stress was similar in all groups, pulmonary apoptosis and proliferation were altered. Our results thus indicate that the hyperglycemic priming of the fetal lung modifies the deleterious effect of hyperoxia on alveolarization in neonatal rats.

Simulations of the equatorial thermosphere anomaly: Physical mechanisms for crest formation

Several mechanisms including heat transport due to zonal winds, chemical heating and field‐aligned ion drag have been proposed to explain the formation of the Equatorial Thermosphere Anomaly (ETA), but the cause of the ETA crests in thermosphere temperature is still a mystery. Our companion study (Lei et al., 2012) has revealed that the field‐aligned ion drag mainly contributes to the ETA trough, but has little effect on the ETA crests. In this study, the mechanisms of heat transport associated with zonal winds and chemical heating due to recombination are examined to assess their contributions to the production of the ETA crests on the basis of National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (NCAR‐TIEGCM) simulations. Our sensitivity simulations demonstrate that neither heat transport due to zonal winds nor chemical heating is able to explain the formation of the ETA crests. Instead, we found that the formation of the ETA crests is attributed to plasma‐neutral heating which has two peaks in the topside ionosphere aside the magnetic equator. These two peaks, which are largely controlled by the magnetic field, are the results of energy transfer from thermal electrons and ions to the neutrals through collisions due to their temperature differences, albeit the ultimate source of this heating is solar radiation which produces photoelectrons that mainly depend on solar zenith angle. The TIEGCM simulations show that the crests of the ETA always locate poleward by 10°–15° with respect to those of the Equatorial Ionosphere Anomaly (EIA), although the trough location of the ETA resembles that of the EIA. The location of the ETA crests is associated with the two‐hump structure in plasma‐neutral collision heating which is small inside the EIA region and larger at the poleward edge of this region.

The Fermi-Pasta-Ulam recurrence and related phenomena for 1D shallow-water waves in a finite basin

Different regimes of the Fermi-Pasta-Ulam (FPU) recurrence are simulated numerically for fully nonlinear “one-dimensional” potential water waves in a finite-depth flume between two vertical walls. In such systems, the FPU recurrence is closely related to the dynamics of coherent structures approximately corresponding to solitons of the integrable Boussinesq system. A simplest periodic solution of the Boussinesq model, describing a single soliton between the walls, is presented in analytic form in terms of the elliptic Jacobi functions. In the numerical experiments, it is observed that depending on the number of solitons in the flume and their parameters, the FPU recurrence can occur in a simple or complicated manner, or be practically absent. For comparison, the nonlinear dynamics of potential water waves over nonuniform beds is simulated, with initial states taken in the form of several pairs of colliding solitons. With a mild-slope bed profile, a typical phenomenon in the course of evolution is the appearance of relatively high (rogue) waves, while for random, relatively short-correlated bed profiles it is either the appearance of tall waves or the formation of sharp crests at moderate-height waves.

A 1‐D morphodynamic model for rill erosion

The key objective of this paper is to develop a 1‐D hydrodynamic and sediment transport model, namely, RILL1D, that handles transcritical flows over abrupt changes (e.g., formation of pool crests and width change) in a single rill and also predicts changes in rill bed elevation. Replication of rill conditions in terms of flow and bed evolution changes necessitated the use of an enhanced TVD‐MacCormack scheme with implementation of Tseng's surface gradient method, to provide an oscillation free solution over formed pool crests. The model at the end of each time step calculates the flow depth, velocity, and bed shear stress and provides changes in bed elevation and grain size distribution within a cell. The hydrodynamic performance of RILL1D is evaluated by comparing its results with either analytical solutions or experimental observations from various benchmark tests with rigid bed conditions that include (1) formation of a hydraulic jump in a rectangular channel, (2) steady subcritical and transcritical flow (without a shock) over a hump, (3) formation of a hydraulic jump in a converging‐diverging frictionless channel, and (4) flows over step‐pools. It is shown that the enhanced TVD‐MacCormack scheme adequately simulates transcritical flows by preserving the mass conservation and reducing the artificial numerical error. The scheme also approximates satisfactorily depth and velocity for a single rill, with a fixed bed consisting of steps and pools, except near the pool headwalls where a backroller forms with negative velocities. The sediment component of RILL1D is evaluated by two field investigations of single rills with mobile beds. With the field data the code is tested for its ability to reproduce measured values of sediment transport rates. A sensitivity analysis is performed to assess the effects of cell size and critical erosional strength in the predictive ability of the model. RILL1D performs reasonably well in these simulations in terms of sediment prediction rates and fared adequately in terms of replicating rill bed morphology.

Glucocorticoid receptor disruption delays structural maturation in the lungs of newborn mice

In order to better understand the regulation of lung maturation by glucocorticoid-glucocorticoid receptor signaling, we studied glucocorticoid receptor (GR) hypomorphic mice with a mixed C57Bl6/129 sv background, in which disruption of exon 2 of the GR gene produces an N-terminal truncated GR protein. Four groups of mice were compared: homozygous mice that die at birth (non-survivors), homozygous mice that survive the neonatal period (survivors), heterozygotes and wild-type mice. Newborn non-survivors had 50% thicker airspace walls and a 46% decrease in the formation of secondary crests (the beginning of alveolar secondary septation) compared to either survivor or wild-type littermates (n = 9 mice in each group). The lung tissue to airspace ratio in homozygous mice not expressing wild-type GR (non-survivor and survivor) was increased compared to heterozygotes and wild-type mice that do express wild-type GR (0.91 +/- 0.08 vs. 0.49 +/- 0.02, n = 4 in each of the four subgroups), suggesting that complete morphological maturation of the lung is dependent on effective glucocorticoid signaling through a fully functional GR. Moreover, the relatively mature lung morphology of survivor versus non-survivor newborns suggests that a partial reduction in mesenchymal thickness is compatible with capillary remodeling, alveolar septation, and viable respiratory function after birth. Our findings suggest that in mice homozygous for disrupted GR, the severity of newborn respiratory insufficiency correlates with the degree of lung structural immaturity.

Collisionally regenerated dark matter structures in galactic nuclei

We show that the presence of a $\ensuremath{\rho}\ensuremath{\sim}{r}^{\ensuremath{-}3/2}$ dark matter overdensity can be robustly predicted at the center of any galaxy old enough to have grown a power-law density cusp in the stars via the Bahcall-Wolf mechanism. Using both Fokker-Planck and direct $N$-body integrations, we demonstrate collisional generation of these dark matter ``crests'' (collisionally regenerated structures) even in the extreme case that the density of both stars and dark matter were previously lowered by slingshot ejection from a binary supermassive black hole. The time scale for collisional growth of the crest is approximately the two-body relaxation time as defined by the stars, which is $\ensuremath{\lesssim}10\text{ }\text{ }\mathrm{Gyr}$ at the centers of stellar spheroids with luminosities $L\ensuremath{\lesssim}{10}^{9.5}{L}_{\ensuremath{\bigodot}}$, including the bulge of the Milky Way. The presence of crests can robustly be predicted in such galaxies, unlike the steeper enhancements, called ``spikes,'' produced by the adiabatic growth of black holes. We discuss special cases where the prospects for detecting dark matter annihilations from the centers of galaxy halos are significantly affected by the formation of crests.

The dynamics of travertine dams

We present a simple, abstract model for travertine dam formation. The simulation uses a depth-averaged hydrodynamic code, coupled with an empirical precipitation model where surface-normal growth rate is proportional to local flow rate. The dynamics of the resulting formation, coarsening and migration (progradation) of crests is demonstrated and compared with field observations. The local self-enhancement of crests, due to increasing flow rate, in combination with lateral inhibition due to upstream drowning, implies a classical pattern formation system with a characteristic dam size, however this wavelength is not stable but increasing. The model also reproduces crest lobes, step bunching and other processes that contribute to the complex dynamics of travertine systems.

Lo, and the Niche Is Knit: Lysyl Oxidase Activity and Maintenance of Lung, Aorta, and Skin Integrity

Lo, and the Niche Is Knit: Lysyl Oxidase Activity and Maintenance of Lung, Aorta, and Skin Integrity

Finite Element Modeling for Tap Design Improvement in Form Tapping

The form tapping process typically yields unfinished threads known as split crests. Thread quality can be greatly improved by reducing the size and severity of split crest formation. This paper develops a finite element model to simulate form tapping with an eye towards the reduction of split crests. The model is validated against linear scratch experiments, and simulations are compared to actual tapping. The effects of various tap design parameters and tapping process conditions on the formation of split crests are investigated to strive toward an optimal tap design.

A new docodont (Mammalia) from the Middle Jurassic of Kyrgyzstan, central Asia

ABSTRACT Tashkumyrodon desideratus, gen. et sp. nov. from the Middle Jurassic (Callovian) Balabansai Formation near Tashkumyr in Kyrgyzstan is described from a single lower molar. The tooth exhibits the typical structure of a docodont lower molar with the main cusp a connected by crests to the lingual cusps (c and g) and to the mesial cusp b. Tashkumyrodon is plesiomorphic in retaining well developed crests c-d and d-f, and derived in reduction of crest b-g. By formation of crests b-e and e-g (derived), Tashkumyrodon resembles Tegotherium from the Late Jurassic of Mongolia and Sibirotherium from the Early Cretaceous of West Siberia, Russia. Tegotherium is more derived than Tashkumyrodon by the more prominent anterior basin (“pseudotalonid”) and the reduction of the crests distal to cusp c. The Asian docodonts probably represent the sister group of all remaining docodonts, an Euramerican clade characterized by retention of crest b-g and reduction of cusp e as well as crest b-e. Simpsonodon from the Middle Jurassic of England is convergently similar to Tegotherium in development of a “pseudotalonid” and reduction of distal crests.

STUDIES OF SPERMATOGENESIS IN THE HEPATICAE V. BLEPHAROPLAST DEVELOPMENT IN MARCHANTIA POLYMORPHA

Coaxial centrioles and a microtubule organizing center (MTOC) constitute each centrosome in spermatid mother cells of Marchantia polymorpha. During cell division the centrosome separates at its midregion and the two centrioles undergo a planar rotation that brings them to lie somewhat staggered and nearly parallel with their proximal ends embedded in osmiophilic granular material similar in appearance to that of the MTOC. Microtubules of the multilayered structure (MLS) arise in this material below the posterior centriole and parallel to its long axis. The rotation of centrioles and the initiation of S1 tubules below the posterior centriole determine polarity of the incipient blepharoplast. Lower MLS strata are formed under the anterior centriole by the compaction of granular, osmiophilic matrix. Formation and growth of S2 vertical lamellae occur at the left front edge of the MLS in association with MTOC‐like matrix localized near the cell membrane. The MLS enlarges to about 0.4 μm wide by 0.6 μm long and is ovoid in outline except for a short distal projection underlying the posterior centriole. Subsequently the lamellae are transformed into homogenous, osmiophilic matrix that contributes directly to the expansion of all MLS strata including microtubules. The stratum of lamellae is interpreted as a planar MTOC subject to morphogenetic control. Each of the four strata grows proximally while the tapering distal projection lengthens beneath the posterior basal body. Dense matrix above the MLS, apparently elaborated by the S2 layer, is organized into cartwheel and triplet components of the basal bodies’ proximal extensions. Organization of triplet tubules proceeds from proximal to distal toward preexisting triplets. Osmiophilic matrix contributes to the formation of microtubule keels and osmiophilic crests and may serve as a cementing material that stabilizes the spatial relationships of blepharoplast components. After full expansion of the MLS’ lower strata, the S2 layer is reorganized into lamellae. Flagellar growth in Marchantia is postulated to involve a process whereby subunits or their precursors are elaborated by the MLS, translocated to the distal end of the flagellum and incorporated into the axonemal tubules. When MLS microtubules elongate to form a long, narrow band, the distal half of the S2 layer is again in the osmiophilic matrix state.

Cyclical changes in the epididymis of the goose, Anser melanotus

ABSTRACT The epididymis of Anser melanotus consists of three components, the rete testis, vasa efferentia, and epididymal tubules. The histological structure and the relationships between the three components of avian epididymis are similar to those existing in the mammalian epididymis. The epididymis shows periodic changes in its histological structure, which are parallel to the changes in the testis. The rete testis consists of wide, anastomosing, cavernous channels, the rete tubules, lines with a simple non-secretory epithelium of cuboidal and columnar non-ciliated cells. During the breeding season the diameter of the rete tubules undergoes an appreciable increase. The internal epithelium becomes squamous through considerable distension. The efferent ducts are lined by groups of columnar ciliated cells alternating with non-ciliated cubical cells, both the types showing secretory activity in the progressive and reproductive phases of the testicular cycle. The internal epithelium of the efferent ducts is thrown into longitudinal folds, leading to the formation of crests and crypts, which give a festooned appearance to the lumen. The epididymal tubules are lined with columnar ciliated cells. During the onset of reproductive period, the epithelial cells of the epididymal tubules hypertrophy and become secretory. The secreted droplets are discharged into the tubule lumina. During the breeding season the epididymal tubules are filled with sperms. In the refractory phase of the testis cycle the epididymal tubules present an embryonic appearance and have no limiting membrane. Groups of cells similar to those which constitute the lining of the tubules can be seen. These cords of cells become bigger by the division of the pre-existing cells and lumina then appear in the centre, leading to the formation of new tubules. The epididymal secretion gives a stimulus to the spermatozoa different from that given by the testis; it brings about the ripening changes in the spermatozoa. There is no influence in the epididymis which can indefinitely preserve the vitality of sperms. The unejaculated spermatozoa left over in the epididymis after the breeding season is finished, either undergo dissolution in the lumina of the tubules or penetrate into the epithelial lining of the efferent ducts and epididymal tubules or even into the surrounding connective tissue, to undergo degeneration there.

SECONDARY WAVE CREST FORMATION

The critical condition for the formation of secondary wave crests in shallow water has been studied using a wave channel 3ft. deep by 1ft. wide by 60ft. long. In the preliminary experiment a horizontal model reef with a vertical drop at its seaward end was installed in order to extend the results of Mason and Keulegan. In later tests this model reef was taken out and the experiment was conducted for a horizontal bottom extending over the entire length of wave channel. The theoretical criterion introduced by Miche was found to be a fairly reliable index.

CRANIAL CRESTS IN THE ANTHROPOIDEA

SUMMARY In young monkeys and apes, and human skulls of all ages, the cranial attachments of the temporalis and nuchal muscles are completely separate. As the permanent teeth erupt, the facial skeleton grows much faster than the cranium, and the correlated development of the temporalis and nuchal muscles results in the formation of bony crests in the occipital region (nuchal crests) and sometimes also in the mid‐sagittal line of the skull (sagittal crests). The crests are most powerfully developed in the gorilla, especially in males, where a nuchal crest may eventually become a uniform shelf of bone as much as 4 cm. wide. A sagittal crest begins to form in the region immediately anterior to the inion. It is present in all males, and may be as much as 5 cm. high. It is found in only about two in every five females. In the adult chimpanzee, the nuchal shelf is formed only in the middle part of the arc between the mastoid and inion, and even in males does not project more than 0–6 cm. A sagittal crest is never found in female chimpanzees. A sagittal ridge or small crest develops in about one male in six. It begins to form mid‐way between the bregma and lambda. In the orang‐utan, the nuchal crest varies in its development. Occasionally it forms a continuous shelf from mastoid to mastoid, and sometimes it is present in only the middle part of the arc between the mastoid and the inion. A sagittal crest develops in up to seven out of every ten adult males, but in only about one adult female in twenty. It begins to form in the region mid‐way between the bregma and lambda. In the gibbon the nuchal crest seldom projects more than 0–1 or 0–2 cm., and extends over only the middle part of the arc between the mastoid and inion. Even in adults, and in contrast to the condition found in most apes and monkeys, the temporal lines are often closest together in the region of the bregma. Very rarely they meet to form a sagittal ridge in this region. In the adult white‐nosed monkey, the nuchal crest occupies at most only the middle third of the arc between the mastoid and the inion. A sagittal crest is present in about one adult male monkey in ten, but never in adult females. It may develop near the bregma, near the inion, or at both points simultaneously. It extends along the whole length of the sagittal suture in less than one male skull in twenty. In the adult male baboon, the nuchal shelf may extend uninterruptedly from mastoid to mastoid, and may project as much as 0–5 cm. In some males and in all females it extends for only a short distance behind the mastoid. The sagittal crest forms in the region immediately anterior to the inion in practically all adult males. In the female the temporal lines may touch immediately anterior to the lambda, but a true crest does not develop. In the woolly monkey, the nuchal crest is weakly developed behind the mastoid. Even in adult males it seldom extends for more than 2 cm. and projects at the most for 0–05 cm. In some adult females not even a nuchal crest is formed. No sagittal ridge or crest was found in any of the skulls of this type of monkey that were examined. The growth processes underlying the formation of the cranial crests are similar throughout the Primates, variations between different species resulting from differences in the relative speed of growth and in the point at which growth stops. Thus: In all primate species the posterior fibres of the temporalis muscles grow more rapidly than the middle and anterior groups, and consequently first approximate to the upper advancing edge of the nuchal muscles at a point between the mastoid and inion. In young animals in which only the milk teeth are in place, the temporal lines are closest together immediately posterior to the glabella. Subsequently, however, as the middle fibres of the temporalis muscle grow more rapidly than the anterior ones, the point of least separation moves backwards to the region of the bregma. Further growth may result in their meeting in the mid‐sagittal line of the skull, at a variable point between the bregma and lambda to form a sagittal crest. In both fossil and living man, the temporalis and nuchal muscles do not approximate, and neither a nuchal nor a sagittal crest is ever formed. The evidence for the three available specimens of Paranthropus crassidens, in which a sagittal crest is present, suggests that the cranial crests of the Australopithecinae developed according to the general pattern which prevails in living monkeys and apes.