Preserved soft anatomy confirms shoulder-powered upstroke of early theropod flyers, reveals enhanced early pygostylian upstroke, and explains early sternum loss.

Anatomy of the first flying feathered dinosaurs, modern birds and crocodylians, proposes an ancestral flight system divided between shoulder and chest muscles, before the upstroke muscles migrated beneath the body. This ancestral flight system featured the dorsally positioned deltoids and supracoracoideus controlling the upstroke and the chest-bound pectoralis controlling the downstroke. Preserved soft anatomy is needed to contextualize the origin of the modern flight system, but this has remained elusive. Here we reveal the soft anatomy of the earliest theropod flyers preserved as residual skin chemistry covering the body and delimiting its margins. These data provide preserved soft anatomy that independently validate the ancestral theropod flight system. The heavily constructed shoulder and more weakly constructed chest in the early pygostylian Confuciusornis indicated by a preserved body profile, proposes the first upstroke-enhanced flight stroke. Slender ventral body profiles in the early-diverging birds Archaeopteryx and Anchiornis suggest habitual use of the pectoralis could not maintain the sternum through bone functional adaptations. Increased wing-assisted terrestrial locomotion potentially accelerated sternum loss through higher breathing requirements. Lower expected downstroke requirements in the early thermal soarer Sapeornis could have driven sternum loss through bone functional adaption, possibly encouraged by the higher breathing demands of a Confuciusornis-like upstroke. Both factors are supported by a slender ventral body profile. These data validate the ancestral shoulder/chest flight system and provide insights into novel upstroke-enhanced flight strokes and early sternum loss, filling important gaps in our understanding of the appearance of modern flight.

Development of an Algorithm to Determine Which Costal Cartilage to Harvest.

Rib graft is a common source of cartilage in rhinoplasty. Donor site choices for this resource were identified according to the authors who presented the introduction of this technique. However, the scientific basis of this valuable method lacks information, including the anatomical properties of costal cartilage. In this study, cartilage radioanatomy is examined and tested for if any estimators are present. A total of 148 thoracal CT scans of patients who applied to our facility were analyzed. Patients were divided per their sex and age of 35, and rib cartilage dimensions, including axial length between the sternal and costal ends of the cartilage (TotL), posteroanterior diameters at the sternal end (StDia), costal end (CosDia), the thickest part (MaxDia) as diametrical parameters and vertical height at the thickest part (h) were recorded. Length of the sternum (St), the axial length of the clavicle (ClavL), the distance of the sixth rib from the anterior axillary border (AntAx), and thorax circumferences at the level of both pectoralis major muscle origin (ThC) and nipples (BrC) were recorded. Statistical analyses were done for correlations. St, ClavL, ThC, and BrC were found to have the most correlated measurements in groups with the age of 35 and less of both genders, and the relations were lost in older groups. Thorax shape may change after the age of 35 years, but in younger patients, St in females and ClavL in males can be used as estimators of cartilage amount.

The utility of sternum in creating a biological profile: A review and future directions.

This review delves into the forensic utility of the sternum in creating a biological profile, focusing on sex, stature, and age estimation. Emphasizing the sternum's significance in challenging scenarios, the study supports the combined length of the manubrium and sternal body as a crucial indicator in sex and stature estimation. However, it highlights the need for caution in applying findings across diverse populations and questions the reliability of Hyrtl's law. Age estimation, primarily based on morphological changes and ossification ages, is explored, with one study showing promise but requiring further validation. While acknowledging the sternum's advantages, the review underscores potential limitations and the absence of specific studies on ancestry estimation, leaving this aspect open for future research. In conclusion, the review provides a comprehensive overview of the sternum's forensic applications, urging continued research to enhance accuracy and applicability.

[Morphology of sternum for formation of the biological profile of unidentified individual]. / Morfologiya grudiny dlya formirovaniya biologicheskogo profilya neopoznannogo individa.

Identification of a person by general group characteristics does not lose its relevance over a long period. An analysis of publications (2000-2023) devoted to the possibilities of using the sternum to determine gender and age showed a fairly large amount of work on this topic, with very promising results. The trend in the development of this area is the use of modern methods of medical imaging. This becomes the starting point for conducting such studies on the territory of the Russian Federation and developing a methodology that includes the Russian population, taking into account their population characteristics.

Prevalence and morphometry of sternal and xiphoid foramen: a meta-analysis on 16,666 subjects.

PURPOSE: Sternal foramen is a perforation of the sternum that can be a source of misdiagnosis during radiographic imaging or life-threatening perforations during bone marrow sampling. The aim of this study was to conduct a meta-analysis on the prevalence, morphometrics, and location of foramen in the sternal body and xiphoid process, describe morphometric features of this phenomenon, and thus verify its clinical importance. Moreover, our secondary outcome was to compare effectiveness of various imaging methods in diagnosis of the sternal or xiphoid foramen. METHODS: A comprehensive search was conducted on major scientific databases to identify studies containing relevant information. Data on foramen's prevalence, location, morphometrics, and accompanying findings were extracted and pooled into a meta-analysis using MetaXL 5.0. RESULTS: Thirty-five studies (n = 16,666 subjects) were included. The overall pooled prevalence of a foramen in the sternal body and/or a xiphoid process was 8.9% (95% CI 6.5-11.7) and it equaled 6.5% (95% CI 5.6-7.6) for sternal body alone and 2.9% (95% CI 0.5-6.9) for the xiphoid process. The foramen was more prevalent in males than in females (12.2% vs. 6.8%). The prevalence of sternal foramen was higher in South American [13.9% (95% CI 11.2-16.9)] and African [13.6% (95% CI 9.7-18.0)] studies compared to North American [6.2% (95% CI 5.0-7.5)] and European populations [8.6% (95% CI 3.1-16.3)]. Mean transverse and vertical diameter of foramen equaled 4.7 mm (95% CI 3.8-5.5), and 5.6 mm (95% CI 4.2-6.9), respectively. CONCLUSION: Our analysis proves that the sternal foramina are structures of significant prevalence and size. Any physician should keep them in mind when performing punctures in this area.

The relationship between sternum variation and mode of locomotion in birds.

BACKGROUND: The origin of powered avian flight was a locomotor innovation that expanded the ecological potential of maniraptoran dinosaurs, leading to remarkable variation in modern birds (Neornithes). The avian sternum is the anchor for the major flight muscles and, despite varying widely in morphology, has not been extensively studied from evolutionary or functional perspectives. We quantify sternal variation across a broad phylogenetic scope of birds using 3D geometric morphometrics methods. Using this comprehensive dataset, we apply phylogenetically informed regression approaches to test hypotheses of sternum size allometry and the correlation of sternal shape with both size and locomotory capabilities, including flightlessness and the highly varying flight and swimming styles of Neornithes. RESULTS: We find evidence for isometry of sternal size relative to body mass and document significant allometry of sternal shape alongside important correlations with locomotory capability, reflecting the effects of both body shape and musculoskeletal variation. Among these, we show that a large sternum with a deep or cranially projected sternal keel is necessary for powered flight in modern birds, that deeper sternal keels are correlated with slower but stronger flight, robust caudal sternal borders are associated with faster flapping styles, and that narrower sterna are associated with running abilities. Correlations between shape and locomotion are significant but show weak explanatory power, indicating that although sternal shape is broadly associated with locomotory ecology, other unexplored factors are also important. CONCLUSIONS: These results display the ecological importance of the avian sternum for flight and locomotion by providing a novel understanding of sternum form and function in Neornithes. Our study lays the groundwork for estimating the locomotory abilities of paravian dinosaurs, the ancestors to Neornithes, by highlighting the importance of this critical element for avian flight, and will be useful for future work on the origin of flight along the dinosaur-bird lineage.

New methods for sex estimation using sternum and rib morphology.

Sex estimation of skeletal remains is of great importance in the fields of physical and forensic anthropology. Since skeletons are often incomplete, it is essential to estimate sex from as many skeletal remains as possible. The aim of this study was to establish new methods for estimating sex using the morphology of the sternum and the fifth to ninth ribs. We considered two conditions of skeletal preservation: All skeletal elements measured are available, or only a single element is available. Traditional or virtual measurements were carried out on three samples: (1) A skeletal sample from the Hamann-Todd Human osteological collection, Cleveland Museum of Natural History, USA (N = 413), was used to create prediction equations for sex estimation. (2) A recent, CT-based sample from Israel (N = 33) was used to cross-validate the accuracy of the prediction equations. (3) A skeletal sample from the Anthropological Collection at Tel Aviv University (N = 15) was used to test the validity of the virtual measurements. Reliability and validity analyses were carried out via intraclass correlation coefficient analysis. Prediction equations for sex were created using logistic regression. The measurements were found to be highly reliable and valid. Success rates for sex estimation were high (> 80%) and correspond well between the skeletal and recent samples, especially for the left sixth, left eigth, and left ninth ribs. To conclude, measurements of the sternum and ribs are valuable for estimating sex and can be carried out using either traditional or virtual tools. Of all the skeletal elements examined in this study, the sternum, left sixth, left eighth, and left ninth ribs were found to be the most reliable skeletal elements for estimating the sex of an individual.

Optimum chest compression point might be located rightwards to the maximum diameter of the right ventricle: A preliminary, retrospective observational study.

BACKGROUND: Some researchers have reported that applying compression closer to the maximum diameter of the left ventricle (Point_max.LV) is associated with worse clinical outcomes, challenging its traditional position as optimum compression point (Point_optimum). By locating the mid-sternum (the actual compression site) in terms of Point_max.LV and its right ventricular equivalent (Point_max.RV), we aimed to determine its optimum horizontal position associated with increased chances of return of spontaneous circulation (ROSC). METHODS: A retrospective, cross-sectional study was performed at a university hospital from 2014 to 2019 on non-traumatic out-of-hospital cardiac arrest (OHCA) victims who underwent chest computed tomography. On absolute x-axis, we designated the x-coordinate of the mid-sternum (x_mid-sternum) as 0 and leftward direction as positive. Re-defining the x-coordinate of Point_max.RV and Point_max.LV as 0 and 1 interventricular unit (IVU), respectively, we could convert x_mid-sternum to "-x_max.RV/(x_max.LV - x_max.RV) (IVU)." Using multiple logistic regression analysis, we investigated whether this converted x_mid-sternum was associated with clinical outcomes, adjusting core elements of the Utstein template. RESULTS: Among 887 non-traumatic OHCA victims, 124 [64.4 ± 16.7 years, 43 women (34.7%)] were enrolled. Of these, 80 (64.5%) exhibited ROSC. X_mid-sternum ranging from -1.71 to 0.58 (-0.36 ± 0.38) IVU was categorised into quintiles: <-0.60, -0.60 to -0.37, -0.37 to -0.22, -0.22 to -0.07 and ≥-0.07 (reference) IVU. The first quintile was positively associated with ROSC (odds ratio [95% confidence interval], 9.43 [1.44, 63.3]). CONCLUSION: Point_optimum might be located far rightwards to Point_max.RV, challenging the traditional assumption identifying Point_optimum as Point_max.LV.

Correlation between Sternal Slope Angle and Primary Spontaneous Pneumothorax in Young Males, a Propensity Score Match Analysis.

It is generally accepted that primary spontaneous pneumothorax (PSP) is found mostly in tall, thin young males. However, the precise etiology of PSP is unclear. We compared some thoracic structural angles of PSPs and controls in young males to determine the predominant factor. CT data of 43 male PSPs (age 21.88 ± 5.30) and 30 controls (age 21.47 ± 5.47) were collected. The angle of thoracic vertebrae slope (∠α), sternal slope angle (∠ß), and tracheal-sternal stem angle (∠γ) were measured in the sagittal position. Carina angle (∠δ) was measured in the coronal position. After a propensity score match (PSM) of age and smoking history, the angles were comparatively evaluated. There were significant differences in all four angles between two unmatched groups, while only in three (∠ß, ∠γ, and ∠δ) after PSM was performed. The correlation between âˆ ß and PSP was most significant, and R2 was 0.456. The prediction accuracy of âˆ ß was 81.3%, OR was 1.386, 95% confidence interval was (1.095-1.754). The sternal slope angles in PSPs are greater than controls indicate the sternal slope angle is associates with the development of PSP and it could be a thoracic structural index to predict the risk of PSP occurrence. Clin. Anat. 33:605-609, 2020. © 2019 Wiley Periodicals, Inc.

The medial-central septum based mammaplasty: A reliable technique to preserve nipple-areola complex sensitivity in post bariatric patients.

INTRODUCTION: Massive weight loss is associated with the ptosis of the breast, loss of the upper pole fullness, medialization of the nipples and volume depletion. Post bariatric patients often need breast reshaping with mastopexy or breast reduction. We report the author's experience with the medial central septum based mammoplasty for breast reshaping after massive weight loss. METHODS: We retrospectively reviewed the records of 85 women who underwent a medial-central septum based mammaplasty, analyzing patients (age, BMI, comorbidities) and operation specific characteristics' (surgical technique, complications) to identify the advantages and the drawbacks of the adopted technique. All the procedures were performed at a single institution by the senior author of this article. RESULTS: 85 patients were included in the review, in total 170 medial-central septum based mammaplasty were performed over a five years period. Early complications, as hematoma and seroma occurred in 2 patients. No total or partial nipple-areola losses were recorded and the viability of the nipple-areola complex (NAC) was excellent in all the treated patients. Sensation was retained in all breasts. Nine patients showed delayed wound healing at the joint of the T scar; in 5 patients we observed spreading scars. CONCLUSION: The medial-central septum based mammaplasty seems to be an effective and safe choice for breast reshaping after massive weight loss, as none of our patients experienced nipple loss and all of them reported good nipple sensation. Moreover, the technique is versatile and can be applied to patients with hypertrophic breasts or gigantomastia.

Validation of age and height based formulae to predict paediatric airway distances - a prospective observational study.

Background: Preoperative airway evaluation in children is an important part of routine preanesthetic evaluation before surgery. External airway measurements, viz., thyromental, mentohyoid, and sternomental distances, while being growth dependent, could identify pediatric patients with potentially difficult airways. Objectives: This study was conducted to validate the age- and height-based formulae, derived from a previous study conducted in our institute, to predict thyromental distance, sternomental distance, and mentohyoid distance in relation with the height and age of pediatric patients. Design: Prospective cross-sectional single arm observational study. Setting: Tertiary level university teaching hospital from July 2015 to December 2016. Patients: Children (202) in the age group of 3-15 years with no obvious external airway anomaly scheduled for elective surgery under general anesthesia. Outcomes Measured: The thyromental, mentohyoid, and sternomental distances were measured preoperatively. The same parameters were then calculated based on age- and height-related formulae derived in the earlier study. Results: Bland-Altman analysis of the sample patients showed a mean difference (bias) between measured and calculated values ranging from 0.14 to -0.60 (3 - 13%). Overall agreement in terms of bias were found to be more with height-based equation for mentohyoid distance and thyromental distance and age-based equation for sternomental distance. Conclusion: Our study validates the formulae derived in the earlier study to predict thyromental, mentohyoid, and sternomental distances in children with no obvious external airway anomalies. Further studies are needed to extend the applicability of these formulae in obese children and those with craniofacial anomalies coming for general anesthesia and surgery.

Sex estimation of the sternum by automatic image processing of multi-slice computed tomography images in a Croatian population sample: a retrospective study.

AIM: To determine the sexual dimorphism of the sternum with standard measurements in a contemporary Croatian population sample using multi-slice computed tomography (MSCT) and to compare the data obtained by an automatic with those obtained by a manual approach. METHODS: Five sternal measurements were obtained from MSCT images of 73 men and 55 women and three sternal indices were calculated. Custom image analysis software was developed for automatic segmentation and calculation of sternal measurements. Measurements of sexual dimorphism were automatically calculated and compared with manual measurements. RESULTS: All of the sternal measurements exhibited significant differences between men and women. The discrepancies between manual and automatic measurements ranged from 2.8% to 3.6% of the mean average values obtained with the automatic approach. The most accurate single-variable discriminant function was sternal body length (82.8%), the most accurate index was sternal area (89.1%), and the discriminant function using three variables was manubrium width, sternal body length, and sternal body width (90.6%). CONCLUSION: Sternal measurements are a reliable sex indicator and can be used in forensic casework. Computer-aided measurement methods can accelerate sex estimation and improve its precision and accuracy.

Bilateral supernumerary clavicular heads of sternocleidomastoid muscle in a Korean female cadaver.

Many anatomical variants on the sternocleidomastoid muscle have been reported. In this study, supernumerary clavicular heads of sternocleidomastoid muscle in a Korean female cadaver were bilaterally displayed. The observed supernumerary heads were classified as follows: one sterno-mastoid, one cleido-occipital and one cleido-mastoid on the right side, and one sterno-mastoid-occipital, four cleido-occipitals, and one cleido-mastoid on the left side. The sterno-mastoid and sterno-mastoid-occipital and the cleido-occipital made the superficial layer of the sternocleidomastoid muscle, while others made deep layer. We discussed clinical relevance and developmental basis of these muscular variations important for clinicians and anatomists.

The dominant nutrient foramen at the clavicular midshaft: an anatomical study.

BACKGROUND: The aim of the present study was to describe the prevalence and topography of the dominant nutrient foramen at the clavicle. METHODS: 317 macerated human clavicles (167 right and 150 left) were available for the study. After detecting the dominant nutrient foramen, the total distance from the sternal surface to the examined nutrient foramen was measured. A foramen index (FI) was used for further data processing. RESULTS: We detected a dominant foramen in 300/317 (94.64%) clavicles, which was located in the middle third in 287/300 (95.7%) clavicles. The average clavicular length was measured at 14.9 cm ± 1.0 cm (range 11.6-17.5 cm) with an average foraminal distance from the sternoclavicular joint surface of 7.9 cm ± 1.3 cm (range 0.9-12.6 cm) in total. The mean FI was 53.2% ± SD 7.4% (range 5.5-79.3%). CONCLUSION: The present study provides a topographic mapping of the foraminal area (46-60% of the total clavicular length). The findings help to assess clavicular fracture patterns, which pass through the foraminal area.

Describing the sternalis muscle: a new variant and an amended classification.

PURPOSE: With emphasis on the clinical setting, knowledge of anatomical variation decreases misdiagnoses and surgical complications. We report a previously undocumented variant of sternalis muscle and recommend an augmented classification scheme. METHODS: Dissection of the anterior thoracic wall on an 83-year-old female cadaver revealed bilateral sternalis muscles. The Snosek et al. classification system was referenced to describe the variant types. RESULTS: The right sternalis muscle has a single belly and can be classified using the Snosek et al. classification system as a simple type, right single. The left sternalis muscle presented with three muscle bellies, each having a unique pattern of superior attachments (heads). This variation is previously undocumented and requires a more detailed classification. CONCLUSIONS: We propose the addition of a new subtype of sternalis classification, as well as a modification to the Snosek et al. (Clin Anat 27:866-884, 2014) classification scheme, to include classification of different muscle bellies when multiple are present.

Optimum Chest Compression Point for Cardiopulmonary Resuscitation in Children Revisited Using a 3D Coordinate System Imposed on CT: A Retrospective, Cross-Sectional Study.

OBJECTIVES: The optimum chest compression site (P_optimum) in children is debated: European Resuscitation Council recommends one finger breadth above the xiphisternal joint, whereas American Heart Association proposes the lower sternal half. Using a coordinate system imposed on CT, we aimed to determine the pediatric P_optimum to maximize stroke volume, the key point for successful cardiopulmonary resuscitation, while minimizing hepatic injury. DESIGN: Retrospective, cross-sectional study. SETTING: University hospital. PATIENTS: Children 1-15 years old who underwent chest CT. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We defined zero point (0, 0) as the center of the xiphisternal joint designating leftward and upward directions of the patients as positive on each axis. P_optimum (x_max. left ventricle, y_max. left ventricle) was defined as the center of the maximum diameter of the left ventricle, whereas P_aorta (x_aorta, y_aorta) as that of the aortic annulus. To compress the left ventricle exclusively, y_max. left ventricle should range above the y coordinate of hepatic dome (y_liver_dome) and below y_aorta. Data were presented as median (interquartile range) and compared among age groups 1.0-5.0, 5.1-10.0, and 10.1-15.0 years using Kruskal-Wallis test. For universal application regardless of age, y coordinates were converted into relative ones with unit of sternal top: 1 unit of sternal top was the y coordinate of the sternal top. A total of 163 patients were enrolled, median age 8.8 year (4.2-14.3 yr). Among age groups, no significant difference was observed in y_max. left ventricle, relative y_max. left ventricle, y_aorta, and y_liver_dome: 1.0 cm (0.1-1.9 cm), 0.10 unit of sternal top (0.01-0.18 unit of sternal top), 0.39 unit of sternal top (0.30-0.47 unit of sternal top), and -0.14 unit of sternal top (-0.25 to -0.03 unit of sternal top), respectively. The probability to compress the left ventricle exclusively was greater than or equal to 96% when placing hand at 0.05-0.20 unit of sternal top. Subgroup analysis demonstrated the following regression equation: x_max. left ventricle (mm) = 0.173 × (height in cm) + 13 (n = 106; p < 0.001; R = 0.278). CONCLUSIONS: Theoretically, pediatric P_optimum is located 1 cm (or 0.1 unit of sternal top) above the xiphisternal joint.

Clinical location of the fourth and fifth intercostal spaces as a percent of the length of the sternum.

OBJECTIVES: To verify accurate placement of the precordial ECG leads by identifying the 4th and 5th intercostal spaces as a function of the length of the sternum. This should decrease the percentage of lead misplacement leading to misdiagnoses. METHODS: The population consisted of patients and healthy volunteers. The proposed method compared palpation of the 4th and 5th intercostal spaces to a percentile of the sternal length. Location of the 4th and 5th intercostal space using a simple device was evaluated to assist in proper placement of the precordial leads to obtain accurate diagnosis. RESULTS: The location of the 4th and 5th intercostal space is related to the length of the sternum. It is 77% of the sternal length that measures 15cm for the 4th intercostal space. The position of the V1 and V2 electrodes decreases to 57% when the sternal length is 26cm. Similar data was obtained to locate the 5th intercostal space with proper position of V4-V6 electrodes. Tables are provided to facilitate this process. An instrument was designed to measure the 4th and 5th intercostal space as a function of the sternal length. CONCLUSIONS: The location of the 4th and 5th intercostal space is identified based on the length of the sternum.

Evidence of the sternalis muscle in two South African cadavers.

The sternalis muscle is an infrequent, non-pathological anatomical variant typically misrepresented in a clinical context. It presents with 3-8% prevalence, according to cadaveric studies. The muscles were identified during routine cadaver prosection at the School of Anatomical Sciences, University of the Witwatersrand. Here, we report two cases of the sternalis muscle in two South African White cadavers. Analysis of the sternalis muscles revealed unilaterally present, distinctly defined muscle masses on the right (case number 1, female) and left (case number 2, male) hemithorax, lateral to the sternum. The muscles occurred with a prevalence of 2.25% within the cadaveric population examined. The prevalence of the sternalis muscle is generally low, especially in the European population. Their presence represents the remnants of the cutaneous muscles in the ventral thorax of lower animals. Clinically, the sternalis muscle may be misinterpreted as a pathological mass or lesion, thus accurate knowledge regarding its variations and prevalence is of importance.

On the absence of sternal elements in Anchiornis (Paraves) and Sapeornis (Aves) and the complex early evolution of the avian sternum.

Anchiornis (Deinonychosauria: Troodontidae), the earliest known feathered dinosaur, and Sapeornis (Aves: Pygostylia), one of the basalmost Cretaceous birds, are both known from hundreds of specimens, although remarkably not one specimen preserves any sternal ossifications. We use histological analysis to confirm the absence of this element in adult specimens. Furthermore, the excellent preservation of soft-tissue structures in some specimens suggests that no chondrified sternum was present. Archaeopteryx, the oldest and most basal known bird, is known from only 10 specimens and the presence of a sternum is controversial; a chondrified sternum is widely considered to have been present. However, data from Anchiornis and Sapeornis suggest that a sternum may also have been completely absent in this important taxon, suggesting that the absence of a sternum could represent the plesiomorphic avian condition. Our discovery reveals an unexpected level of complexity in the early evolution of the avian sternum; the large amount of observable homoplasy is probably a direct result of the high degree of inherent developmental plasticity of the sternum compared with observations in other skeletal elements.

Regulatory modulation of the T-box gene Tbx5 links development, evolution, and adaptation of the sternum.

The sternum bone lies at the ventral midline of the thorax where it provides a critical attachment for the pectoral muscles that allow the forelimbs to raise the body from the ground. Among tetrapods, sternum morphology is correlated with the mode of locomotion: Avians that fly have a ventral extension, or keel, on their sterna, which provides an increased area for flight muscle attachment. The sternum is fused with the ribs attaching on either side; however, unlike the ribs, the sternal precursors do not originate from the somites. Despite the crucial role of the sternum in tetrapod locomotion, little attention has been given to its acquisition, evolution, and embryological development. We demonstrate an essential role for the T-box transcription factor gene Tbx5 in sternum and forelimb formation and show that both structures share an embryological origin within the lateral plate mesoderm. Consistent with this shared origin and role of Tbx5, sternum defects are a characteristic feature of Holt-Oram Syndrome (OMIM 142900) caused by mutations in TBX5. We demonstrate a link between sternum size and forelimb use across avians and provide evidence that modulation of Tbx5 expression underlies the reduction in sternum and wing size in a flightless bird, the emu. We demonstrate that Tbx5 is a common node in the genetic pathways regulating forelimb and sternum development, enabling specific adaptations of these features without affecting other skeletal elements and can also explain the linked adaptation of sternum and forelimb morphology correlated with mode of locomotion.