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Domestication shaped wolves into dogs and transformed both their behavior and their anatomy. Here we show that, in only 33,000 y, domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans. Based on dissections of dog and wolf heads, we show that the levator anguli oculi medialis, a muscle responsible for raising the inner eyebrow intensely, is uniformly present in dogs but not in wolves. Behavioral data, collected from dogs and wolves, show that dogs produce the eyebrow movement significantly more often and with higher intensity than wolves do, with highest-intensity movements produced exclusively by dogs. Interestingly, this movement increases paedomorphism and resembles an expression that humans produce when sad, so its production in dogs may trigger a nurturing response in humans. We hypothesize that dogs with expressive eyebrows had a selection advantage and that “puppy dog eyes” are the result of selection based on humans’ preferences.

The facial nerve is the seventh cranial nerve, and its temporal branch (TBFN) innervates the frontalis muscle. Peripheral nerve disorders involving the facial nerve can lead to facial palsy, for which a common non-invasive treatment approach is to inject a chemodenervation agent such as botulinum toxin (BoNT). The purpose of this study was to provide anatomical suggestions for BoNT injection sites in the frontalis muscle based on the intramuscular innervation pattern of the TBFN as identified objectively using Sihler’s staining. Nineteen hemifaces containing the TBFN and the frontalis muscle were harvested from 15 embalmed cadavers according to facial landmarks. The frontalis muscle was divided into 16 areas to identify the prevalence rates of distal nerve endings and the arborization pattern of the TBFN after applying Sihler’s staining. Distal nerve endings of the TBFN were most commonly found in area B2 (17 of 19 specimens, 89.5%), followed by in area B3 ( n  = 15, 78.9%). No distal nerve ending was observed in area A1. Two types of the arborization pattern of the TBFN were observed. We propose four BoNT injection sites based on the intramuscular innervation pattern of the TBFN in the frontalis muscle as identified using Sihler’s staining.

Botulinum neurotoxin injection surrounding the nose area is frequently used in aesthetic settings. However, there is a shortage of thorough anatomical understanding that makes it difficult to treat wrinkles in the nose area. In this study, the anatomical aspects concerning the injection of botulinum neurotoxin into the nasalis, procerus, and levator labii superioris alaeque muscles are assessed. In addition, the present knowledge on localizing the botulinum neurotoxin injection point from a newer anatomy study is assessed. It was observed that, for the line-associated muscles in the nose region, the injection point may be more precisely defined. The optimal injection sites are the nasalis, procerus, and levator labii superioris alaeque muscles, and the injection technique is advised. We advise the best possible injection sites in association with anatomical standards for commonly injected muscles to increase efficiency in the nose region by removing the wrinkles. Similarly, these suggestions support a more precise procedure.

Computer vision (CV) is widely used in the investigation of facial expressions. Applications range from psychological evaluation to neurology, to name just two examples. CV for identifying facial expressions may suffer from several shortcomings: CV provides indirect information about muscle activation, it is insensitive to activations that do not involve visible deformations, such as jaw clenching. Moreover, it relies on high-resolution and unobstructed visuals. High density surface electromyography (sEMG) recordings with soft electrode array is an alternative approach which provides direct information about muscle activation, even from freely behaving humans. In this investigation, we compare CV and sEMG analysis of facial muscle activation. We used independent component analysis (ICA) and multiple linear regression (MLR) to quantify the similarity and disparity between the two approaches for posed muscle activations. The comparison reveals similarity in event detection, but discrepancies and inconsistencies in source identification. Specifically, the correspondence between sEMG and action unit (AU)-based analyses, the most widely used basis of CV muscle activation prediction, appears to vary between participants and sessions. We also show a comparison between AU and sEMG data of spontaneous smiles, highlighting the differences between the two approaches. The data presented in this paper suggests that the use of AU-based analysis should consider its limited ability to reliably compare between different sessions and individuals and highlight the advantages of high-resolution sEMG for facial expression analysis.

Background The nasal ala region significantly affects facial aesthetics and function. Botulinum toxin injections may enhance nasal appearance, but their precise impact on underlying muscles remains unexplored. Understanding the muscular anatomy and behavior in this area is crucial for optimizing toxin application and achieving desired outcomes. Objective This study aimed to ultrasonographically assess and characterize the muscular architecture of the nasal ala region in 32 participants, with the primary objective of delineating the specific muscles involved in nasal aesthetics. Methods and Materials This cross‐sectional study included 32 participants (15 females and 17 males, aged 20–65) with no history of nasal surgery or botulinum toxin injections in the nasal region. Ultrasonographic evaluation was performed to assess the superficial and deep muscular layers in the nasal ala region, using ultrasonography to visualize the targeted muscles and measure their depth. Results Ultrasonographic analysis revealed distinct muscular structures in the nasal ala region among participants. Simultaneous movements of the associated muscles were observed, exhibiting diverse depths. Conclusion Ultrasonographic evaluation in our study population elucidated the anatomical nuances of the underlying muscles involved in nasal anatomy. These findings establish a foundation for a more targeted and precise approach in administering botulinum toxin injections, potentially optimizing nasal aesthetics outcomes.

PurposeThis study aimed to clarify the structural arrangement of the orbicularis oris (OOr), the buccinator, and the other perioral muscles around the modiolus.MethodsThe perioral muscles in seventeen cadavers fixed with formalin were dissected in situ and/or in isolated muscle specimens, and their layers were reconstructed schematically upon pantomographic view of the skeleton to evaluate their actions.ResultsThe buccinator was composed of three parts including upper and lower oblique parts in its superficial layer and a middle transverse part in its deep layer. The superior and inferior OOr were composed of an inner marginal part (IM) and an outer labial part (OL) in each. The perioral muscles as a whole were arranged in three layers. The first layer consisted of the depressor anguli oris and the OL of superior OOr connected at the modiolus in a vertical direction. The second layer consisted of the upper and inner oblique part of buccinator and a part of the OL of inferior OOr connected at the modiolus in a horizontal direction. The third layer contained the middle transverse part of buccinator continuous with the IM of both OOr and a part of the OL of inferior OOr without connection to the modiolus.ConclusionsThe different arrangement of the three layers of perioral muscles around the modiolus could serve as a good basis to predict the actions of the individual perioral muscles on the movement of lips in open/close of the oral fissure and widening/narrowing of the lip width.

Studies on the muscular-deep fascial system which connects the upper eyelid, brow, and glabella, are lacking. This study aimed to explore the fine anatomy of the muscular-deep fascial system in the region between the eyebrow and the superior orbital margin . We included eight formalin–phenol-embalmed cadavers (16 sides of specimens), and categorized them into anatomical dissections and histological sections. Five cadavers (10 sides) were dissected for gross anatomical observation, whereas all soft tissues of the other three cadavers (6 sides) were dissected for tissue sectioning and histological analysis. Three tissue blocks and 16 strips in each block were trimmed, numbered, and sliced into these specimens. Hematoxylin–Eosin and Masson’s Trichrome staining were performed. In the region between the eyebrow and the superior orbital margin, the frontalis was covered by the orbicularis oculi. Fibers of the frontalis muscle penetrated into the orbicularis oculi muscle bundles, and crosslinked around the eyebrow level. Both the frontalis and the orbicularis oculi were attached to the thickened multilayered deep fascia in this region, which could be regarded as the muscular-deep fascial system. The muscular-deep fascial system connects the frontalis deep fascia and deep forehead compartments down to the orbicularis-supporting ligament. The precise anatomy of the muscular-deep fascial system in the region between the eyebrow and the superior orbital margin may provide a valuable reference for soft-tissue fixation and suspension in facial surgery.

Botulinum toxin injections are a popular cosmetic treatment for smoothing wrinkles. Recent trends emphasize not just wrinkle reduction but also the correction of facial expressions that convey emotions. Among these, the sad face expression, associated with the omega pattern, is often overlooked despite its significant role in emotional expression. This study explored the anatomy and muscle activity related to the sad face expression, focusing on the occipitofrontalis, corrugator supercilii, depressor supercilii, procerus, and orbicularis oculi muscles. A new classification system was developed to categorize this expression based on patient control and muscle strength. The study found that the omega pattern is produced by the interaction of specific facial muscles, with three types of patient muscle control identified: automatic, controllable, and uncontrollable gestures. The visibility of the sad face expression varies among individuals due to differences in muscle strength and control. Incorporating the assessment of the sad face expression into pretreatment evaluations can enhance the effectiveness of botulinum toxin treatments by addressing both aesthetic and emotional aspects of facial expressions. V.

Paleontologists and paleoanthropologists have long debated relationships between cranial morphology and diet in a broad diversity of organisms. While the presence of larger temporalis muscle attachment area (via the presence of sagittal crests) in carnivorans is correlated with durophagy (i.e. hard-object feeding), many primates with similar morphologies consume an array of tough and hard foods—complicating dietary inferences of early hominins. We posit that tapirs, large herbivorous mammals showing variable sagittal crest development across species, are ideal models for examining correlations between textural properties of food and sagittal crest morphology. Here, we integrate dietary data, dental microwear texture analysis, and finite element analysis to clarify the functional significance of the sagittal crest in tapirs. Most notably, pronounced sagittal crests are negatively correlated with hard-object feeding in extant, and several extinct, tapirs and can actually increase stress and strain energy. Collectively, these data suggest that musculature associated with pronounced sagittal crests—and accompanied increases in muscle volume—assists with the processing of tough food items in tapirs and may yield similar benefits in other mammals including early hominins.

Network theory is increasingly being used to study morphological modularity and integration. Anatomical network analysis (AnNA) is a framework for quantitatively characterizing the topological organization of anatomical structures and providing an operational way to compare structural integration and modularity. Here we apply AnNA for the first time to study the macroevolution of the musculoskeletal system of the head and neck in primates and their closest living relatives, paying special attention to the evolution of structures associated with facial and vocal communication. We show that well-defined left and right facial modules are plesiomorphic for primates, while anthropoids consistently have asymmetrical facial modules that include structures of both sides, a change likely related to the ability to display more complex, asymmetrical facial expressions. However, no clear trends in network organization were found regarding the evolution of structures related to speech. Remarkably, the increase in the number of head and neck muscles – and thus of musculoskeletal structures – in human evolution led to a decrease in network density and complexity in humans.