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Stiletto snakes (Atractaspis) resemble vipers in having a short maxilla bearing a long fang associated with a large venom gland. Previous studies of Atractaspis have described an unusual envenomation strategy in which one fang is unilaterally everted from the closed mouth and stabbed into the prey by a posteroventral jerk of the head. Prior anatomical descriptions suggest that the head of Atractaspis is designed for increased cranial kinesis through liberation of both ends of the pterygoid. We combined video records of A. bibroni feeding on live prey inside a narrow tunnel with electrical stimulation of anesthetized snakes and dissection of preserved specimens to show that the apparent design for increased cranial kinesis is constrained minimally by maxillary-prefrontal relationships that limit pterygoid movement. Liberation of the palatine from the pterygoid precludes prey transport. using the 'pterygoid walk' because of the absence of a palatine protraction mechanism. Atractaspis has to rely on a relatively. inefficient transport mechanism in which the snake forces its head over the prey, with lateral rotations around a vertical axis. As the prey enters the esophagus A. bibroni switches to bilateral head and anterior trunk extension and compression, a mechanism that can make use of the palatine teeth. It remains unresolved how an upper jaw with high kinetic potential of the medial elements could evolve together with a lateral upper jaw with limited kinetic potential. Nevertheless, the unusual feeding apparatus of Atractaspis appears to be ideally suited for prey capture in small spaces.

Squamata may be viewed loosely as a clade composed of some species (mostly lizards) that eat plants or crush small prey and other species (many makes) that engulf large prey. In lizards, the quadrate is overlain by dermal bones, preventing its elevation. In snakes (and dibamids), the quadrate attaches to the lateral braincase and elevation of the entire bone is possible in many species. Elongation and reorientation of the quadrate within snakes correlates with increases in the diversity and size of elusive prey selected and with the appearance of rapid strike behavior. A host of structural changes (ear form, relative sizes of head and trunk, forms of palatomaxillary arches and teeth, relative lengths of mandibles, adductor muscle arrangements) may be correlated with the mechanical demands of striking. Hence, prey capture may have driven selection for many of the features necessary for ingestion of large diameter prey in snakes. Conversely, suspensorial design may limit most lizards to exploiting prey of relatively small mass.

Xenopeltis, a snake with unusual skull and cephalic muscle forms, is currently hypothesized to be a basal macrostomatan. Clade membership of Xenopeltis is reassessed on the basis of prey capture and transport mechanics, manipulations of anesthetized animals, and reanalysis of cranial anatomy from dissection and histological sections. These data show that Xenopeltis uses a simple lunge and a driving scissors strike to catch prey. The palatomaxillary apparatus is relatively immobile. Xenopeltis transports prey using occipital and snout shifting and palatomaxillary (PM) packing, a previously undescribed variant of a plesiomorphic mechanism used by Cylindrophis. PM packing depends on ratchet functions provided by hinged teeth on all dentigerous bones and on active depression of the snout, palatine and anterior end of the maxilla. These movements are activated by a large slip of the adductor externus superficialis connecting the prefrontal and dentary. Transport is aided by compressing and extending the anterior trunk. Xenopeltis lacks folded interscale regions between infralabial scales and loose connections between mandibles and skin, limiting separation of mandibular tips and, hence, maximum gape size. All these features indicate that Xenopeltis is not a basal macrostomatan but basal to macrostomatans. Further, rapid transport of relatively large diameter prey by Xenopeltis using snout and occipital shifting suggests these movements are basal to the pterygoid walk. A unilateral pterygoid walk occurs only in clades with the palatines liberated from the snout. Macrostomy evolved secondarily in clades with a unilateral pterygoid walk because other types of transport are ineffective when the mandibular tips are separated widely.

The rodent cheek pouch is an evolutionary novelty that allows quick transport of large amounts of food to a safe environment for storage and consumption. Hamsters are unusual in responding to internal energy deficits by increasing hoarding rather than consumption of food. The hamster cheek pouch opens into the oral cavity, so that the mouth must be opened in order to pouch food. This suggests that pouching motor patterns might be derived from ingestive behavior. We recorded Syrian hamsters (Mesocricetus auratus) chewing and pouching in a mirrored box that provided simultaneous frontal, lateral, and ventral perspectives using video recorded at 60 fps with frame exposures of 1/500 sec. Jaw cycles were evident during pouching, and assisted insertion of food into the pouch. Pouching jaw cycles were similar to masticatory jaw cycles but a delay was often evident between normal fast-open and fast-close phases, particularly when pouching large food items, suggesting modulation of the most complex part of the masticatory motor pattern. The gross anatomy of the cheek pouch and its trapezius-derived retractor muscle combined with visual records of the timing of retractor contraction suggest that the retractor plays a role in filling the pouch. Contraction of the retractor muscle tightens the pouch walls around the food while pulling the pouch and enclosed food caudally, leaving an empty rostral region of the pouch available for more food. We speculate that the neuroanatomical circuits that control the cheek pouch and hoarding behavior might provide a unique opportunity to study the neural basis of hunger motivation vs. food consumption.

One hundred and eighty one white children aged 6 to 11 years who were attending medical outpatient clinics with their mothers were studied to assess the prevalence of psychological disturbance in the children, and anxiety and depression in the mothers. Teachers were also asked to assess the children independently using the Rutter scales. Mothers assessed 70 (39%) of the children as being disturbed, 20 of whom were also assessed as being disturbed by their teachers. A further 15 children were assessed as being disturbed by their teachers but not by their mothers. Thirty five (19%) of the mothers assessed themselves as anxious and two as depressed using the hospital anxiety and depression scale. Anxious and depressed mothers were significantly more likely to assess their child as being disturbed. In contrast, the teachers' assessments of the children were not affected by the mental state of the mothers. These findings confirm that mothers' perceptions of their children are modified by their own moods. [ABSTRACT FROM AUTHOR]

Asian children, excluding recently arrived immigrants, had a similar incidence of tuberculosis to white children in Leeds from 1982-6. Children living in the urban priority area were 2.6 times more likely to develop tuberculosis than those living elsewhere. Selection for infant BCG immunisation should not depend on ethnic group alone. [ABSTRACT FROM AUTHOR]

Anatomy compromises the precision and accuracy of measurements made of the body length and head size of live snakes. Body measures (snout-vent length, SVL) incorporate many synovial intervertebral joints, each allowing flexion and limited extension and compression. Radiographs of the trunk in 14 phylogenetically diverse species in resting and stretched conditions combined with dissections and histological analysis of intervertebral joints show that the synovial nature of these joints underlies the variance in SVL measures. Similarly, the ubiquity and variety of viscoelastic tissues connecting mobile snout and jaw elements of alethinophidian snakes underlie variances in length and width measures of the head. For the overall size of the head and jaw apparatus, the part that can be most easily and relatively precisely measured for many snakes is the mandible because it has only one mobile joint. As to accuracy, the anatomy of intervertebral and cranial joints supports the hypothesis that in living snakes, the head and trunk have no exact size., (© 2024 The Author(s). Journal of Morphology published by Wiley Periodicals LLC.)

The classic view of the vertebrate dorsal root ganglion is that it arises from trunk neural crest cells that migrate to positions lateral to the spinal cord, sending axons dorsally into the spinal cord and dendrites ventrally to meet with motor axons in the ventral root to form spinal nerves. As a result, the ganglion ends up lying in the dorsal root of the spinal nerve. Serial histological sections of parts of the trunk of juveniles of different snake species revealed that the ganglia lie distal to the junction of dorsal and ventral roots of spinal nerves and outside the neural canal. The anatomical position of spinal ganglia in snakes suggests that regulation of trunk neural crest migration in snakes differs from that in the model endotherms in which it has been most thoroughly explored. Dorsal roots have no distinct rootlets and the span of root entry to the spinal cord is short compared to that of ventral rootlets in the same segment. Comparing early developmental stages to juvenile spinal cords shows an increased separation of spinal nerve root sites and ventral migration of the ganglion in later development. Dorsal rami of the spinal nerves leave directly from the dorsal edge of the ganglion, and the ventral ramus leaves from the ventral tip of the ganglion. How these features relate to the developmental regulation of ganglion form and position and the extraordinary locomotor capabilities of the snake trunk are unclear., (© 2022 Wiley Periodicals LLC.)

Genomics is narrowing uncertainty in the phylogenetic structure for many amniote groups. For one of the most diverse and species-rich groups, the squamate reptiles (lizards, snakes, and amphisbaenians), an inverse correlation between the number of taxa and loci sampled still persists across all publications using DNA sequence data and reaching a consensus on the relationships among them has been highly problematic. In this study, we use high-throughput sequence data from 289 samples covering 75 families of squamates to address phylogenetic affinities, estimate divergence times, and characterize residual topological uncertainty in the presence of genome-scale data. Importantly, we address genomic support for the traditional taxonomic groupings Scleroglossa and Macrostomata using novel machine-learning techniques. We interrogate genes using various metrics inherent to these loci, including parsimony-informative sites (PIS), phylogenetic informativeness, length, gaps, number of substitutions, and site concordance to understand why certain loci fail to find previously well-supported molecular clades and how they fail to support species-tree estimates. We show that both incomplete lineage sorting and poor gene-tree estimation (due to a few undesirable gene properties, such as an insufficient number of PIS), may account for most gene and species-tree discordance. We find overwhelming signal for Toxicofera, and also show that none of the loci included in this study supports Scleroglossa or Macrostomata. We comment on the origins and diversification of Squamata throughout the Mesozoic and underscore remaining uncertainties that persist in both deeper parts of the tree (e.g., relationships between Dibamia, Gekkota, and remaining squamates; among the three toxicoferan clades Iguania, Serpentes, and Anguiformes) and within specific clades (e.g., affinities among gekkotan, pleurodont iguanians, and colubroid families)., (© The Author(s) 2019. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Most suction-feeding, aquatic vertebrates create suction by rapidly enlarging the oral cavity and pharynx. Forceful enlargement of the pharynx is powered by longitudinal muscles that retract skeletal elements of the hyoid, more caudal branchial arches, and, in many fish, the pectoral girdle. This arrangement was thought to characterize all suction-feeding vertebrates. However, it does not exist in the permanently aquatic, tongueless Pipa pipa, an Amazonian frog that can catch fish. Correlating high-speed (250 and 500 fps) video records with anatomical analysis and functional tests shows that fundamental features of tetrapod body design are altered to allow P. pipa to suction-feed. In P. pipa, the hyoid apparatus is not connected to the skull and is enclosed by the pectoral girdle. The major retractor of the hyoid apparatus arises not from the pectoral girdle but from the femur, which lies largely within the soft tissue boundaries of the trunk. Retraction of the hyoid is coupled with expansion of the anterior trunk, which occurs when the hypertrophied ventral pectoral elements are depressed and the urostyle and sacral vertebra are protracted and slide forward on the pelvic girdle, thereby elongating the entire trunk. We suggest that a single, robust pair of muscles adduct the cleithra to depress the ventral pectoral elements with force, while modified tail muscles slide the axial skeleton cranially on the pelvic girdle. Combined hyoid retraction, axial protraction, and pectoral depression expand the buccopharyngeal cavity to a volume potentially equal to that of the entire resting body of the frog. Pipa may be the only tetrapod vertebrate clade that enlarges its entire trunk during suction-feeding., (© 2017 Wiley Periodicals, Inc.)

Many snakes swallow large prey whole, and this process requires large displacements of the unfused tips of the mandibles and passive stretching of the soft tissues connecting them. Under these conditions, the intermandibular muscles are highly stretched but subsequently recover normal function. In the highly stretched condition we observed in snakes, sarcomere length (SL) increased 210% its resting value (SL0), and actin and myosin filaments no longer overlapped. Myofibrils fell out of register and triad alignment was disrupted. Following passive recovery, SLs returned to 82% SL0, creating a region of double-overlapping actin filaments. Recovery required recoil of intracellular titin filaments, elastic cytoskeletal components for realigning myofibrils, and muscle activation. Stretch of whole muscles exceeded that of sarcomeres as a result of extension of folded terminal tendon fibrils, stretching of extracellular elastin and independent slippage of muscle fibers. Snake intermandibular muscles thus provide a unique model of how basic components of vertebrate skeletal muscle can be modified to permit extreme extensibility., (© 2014. Published by The Company of Biologists Ltd.)

The gross anatomy of the mouth of snakes has always been interpreted as an evolutionary response to feeding demands. In most alethinophidian species, their anatomy allows limited functional independence of right and left sides and the roof and floor of the mouth as well as wide separation of the tips of the mandibles. However, locations of the tongue and glottis in snakes suggest extraordinary rearrangement of pharyngeal structures characteristic of all vertebrates. Serial histological sections through the heads of a number of colubroid species show muscularis mucosal smooth muscle fibers appearing in the paratracheal gutter of the lower jaw at varying levels between the eye and ear regions. Incomplete muscularis externa elements appear beneath the paratracheal gutter more caudally but typically at otic levels. Both muscle layers encompass more of the gut wall at more posterior levels, encircling the gut at the level of the atlas or axis. The pattern in snakes suggests developmental dissociation of dorsal and ventral splanchnic derivatives and extensive topological rearrangements of some ventral pharyngeal arch derivatives typical of most tetrapods. When snakes swallow large prey, the effective oral cavity becomes extremely short ventrally. The palatomaxillary arches function as ratchets packing the prey almost directly into the esophagus. Our findings raise questions about germ layer origins and regulation of differentiation of gut regions and derivatives in snakes and suggest that significant aspects of the evolution of lepidosaurs may be difficult to recover from bones or molecular sequence data alone., (Copyright © 2014 Wiley Periodicals, Inc.)

The skin of squamates consists of a keratinized epidermis divided into thick scale and thinner, folded interscale regions underlain by a dermis containing a complex array of fibrous connective tissues. We examined the skin of the lower jaw of watersnakes (Nerodia sipedon) to determine how skin morphology changes when highly stretched during ingestion of large prey. Video records of skin behavior in the lower jaws of watersnakes feeding on fish or anesthetized watersnakes being stretched on an Instron machine showed that most skin extension involves the interscale skin. The largest intermandibular separation recorded during feeding was 7.7× resting distance, but intermandibular separation reached 10× without tissue failure during mechanical testing. Histological and anatomical analyses of lower jaws fixed in resting, moderately or highly stretched conditions showed that stretching had little effect on scale regions of the epidermis. However, stretching flattened folds of interscale regions at both gross and cellular levels and imposed changes in epidermal cell shape. Stretching of the dermis is primarily limited to realignment of collagen and stretching of elastin in the deep dermis. The configuration of dermal elastin suggests a model for passive recovery of epidermal folding following release of tension., (© 2013 Wiley Periodicals, Inc.)

Most mammals have deformable bodies, making it difficult to measure the size of living or freshly killed ones accurately. Because small rodents are common prey of many snakes, and because nearly all snakes swallow their prey whole, we explored four methods for determining the ingestible size (the smallest cross-sectional area that the largest part of the rodent can be made into without breaking bones or dislocating joints) of 100 intact rodents, including 50 Musmusculus and 50 Rattus norvegicus. Cross-sectional areas derived from maximal height and width of specimens at rest or the same specimens wrapped snout to pelvic girdle are roughly 1.5× higher than areas calculated either by the height and width of the same specimens rolled into cylinders or by volumetric displacement. Rolling rodents into cylinders reduces cross-sectional area by straightening the vertebral column, lengthening the abdominal cavity, elevating the sternum, compressing the thoracic cavity, and protracting the shoulder joint, that is, changes similar to those seen in rodents eaten by snakes. Reduced major axis regression of the smallest attainable cross-sectional area, y, on mass, x, shows that y (in log mm(2) ) approximates 1.53x (in log grams)(0.69) for rats and 1.63x(0.64) for mice. Our results suggest that visual cues provided by live rodents might lead most predators, like snakes, to overestimate ingestible size and hence rarely attack prey too large to ingest., (Copyright © 2012 Wiley Periodicals, Inc.)

Snakes have long been thought to drink with a two-phase buccal-pump mechanism, but observations that some snakes can drink without sealing the margins of their mouths suggest that buccal pumping may not be the only drinking mechanism used by snakes. Here, we report that some snakes appear to drink using sponge-like qualities of specific regions of the oropharyngeal and esophageal mucosa and sponge-compressing functions of certain muscles and bones of the head. The resulting mechanism allows them to transport water upward against the effects of gravity using movements much slower than those of many other vertebrates. To arrive at this model, drinking was examined in three snake species using synchronized ciné and electromyographic recordings of muscle activity and in a fourth species using synchronized video and pressure recordings. Functional data were correlated with a variety of anatomical features to test specific predictions of the buccal-pump model. The anatomical data suggest explanations for the lack of conformity between a buccal-pump model of drinking and the performance of the drinking apparatus in many species. Electromyographic data show that many muscles with major functions in feeding play minor roles in drinking and, conversely, some muscles with minor roles in feeding play major roles in drinking. Mouth sealing by either the tongue or mental scale, previously considered critical to drinking in snakes, is incidental to drinking performance in some species. The sponge mechanism of drinking may represent a macrostomatan exaptation of mucosal folds, the evolution of which was driven primarily by the demands of feeding., (© 2012 WILEY PERIODICALS, INC.)

Elapid snakes have previously been divided into two groups (palatine erectors and palatine draggers) based on the morphology and inferred movements of their palatine bone during prey transport (swallowing). We investigated the morphology and the functioning of the feeding apparatus of several palatine draggers (Acanthophis antarcticus, Oxyuranus scutellatus, Pseudechis australis) and compared them to published records of palatine erectors. We found that the palatine in draggers does not move as a straight extension of the pterygoid as originally proposed. The dragger palato-pterygoid joint flexes laterally with maxillary rotation when the mouth opens and the jaw apparatus is protracted and slightly ventrally during mouth closing. In contrast, in palatine erectors, the palato-pterygoid joint flexes ventrally during upper jaw protraction. In draggers, the anterior end of the palatine also projects rostrally during protraction, unlike the stability of the anterior end seen in erectors. Palatine draggers differ from palatine erectors in four structural features of the palatine and its relationships to surrounding elements. The function of the palato-pterygoid bar in both draggers and erectors can be explained by a typical colubroid muscle contraction pattern, which acts on a set of core characters shared among all derived snakes. Although palatine dragging elapids share a fundamental design of the palato-maxillary apparatus with all higher snakes, they provide yet another demonstration of minor structural modifications producing functional variants.

The fangs of vipers are extremely long, rotating, hollow teeth. Analysis of video records of more than 750 strikes recorded at 60 or 250 frames per second for 285 individuals representing 86 species in 31 genera shows that vipers reposition fangs after initial contact with prey in more than a third of the strikes. Repositioning resulted when fangs missed prey entirely or hit prey regions that did not permit adequate penetration. The prevalence of repositioning, even among species that normally release prey, suggests strong selective pressure for rapid neuromotor response to fang placement error. The rapidity of repositioning suggests the existence of (a) fine-scale sensory detection of fang penetration depth, (b) rapid modulation of contraction of antagonistic muscles, and (c) possibly neurological modifications to shorten transmission time between sensory input and motor output. Extreme fang length has apparently coevolved with extreme functions.

Video records of swimming water snakes show that during moderate to rapid swimming, the rear half to two-thirds of the trunk is compressed laterally, approaching the body form of some sea snakes. Body form of swimming snakes differed significantly from their shape when resting on a flat surface or when anesthetized and suspended in water. The extent of lateral flattening is positively correlated with swimming speed, a relationship generally supported by tests of trunk models in a flow tank. In Nerodia, the ability to temporarily flatten the trunk depends on kinetic costovertebral joints, a large compressible body cavity, and the absence of ventral skeletal support - features found in most snakes. Histological studies and manipulations of partially dissected preserved specimens showed that the resting angle of the ribs is maintained by localized elastic hypertrophy of the costovertebral capsular ligament. Trunk form during swimming in Nerodia is proposed to arise from anteromedial movement of the distal rib powered by deep muscles acting in concert with those proposed to generate undulation of the vertebral column.

Prodigious food hoarding in Syrian hamsters Mesocricetus auratus Waterhouse is strongly linked to appetite and is made possible by large internal cheek pouches. We provide a functional analysis of the cheek pouch and its associated retractor muscle. Frame-by-frame analysis of videotaped pouch-filling behavior revealed multiple jaw cycles for each food item pouched and the use of more jaw cycles to pouch large food items ( approximately 2.5 g chow pellets) than small (corn kernels or sunflower seed with husks). These results stand in contrast to previously reported pouching kinematics in the externally pouched Dipodomys deserti, which uses only one jaw cycle per pouching event. Comparison of pouching and mastication in the same individuals also suggests that in Syrian hamsters, feeding jaw cycles are modulated to accommodate pouch filling primarily by the addition of a pause between fast open and fast close phases, which we call ;gape phase'. Contrary to previous assertions, the retractor muscle does not merely provide structural support for the full pouch during locomotion. Video analysis of ten hamsters with unilaterally denervated retractor muscles and electrophysiological study of an anaesthetized subject confirmed that retractor muscle activity during pouch filling increases pouching efficiency for food items subsequent to the first.