[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Chest](https://durgical.com/en/anatomy/region/chest/) › External intercostals [Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Chest](https://durgical.com/en/anatomy/region/chest/) # External intercostals The external intercostals are the outer layer of muscles between the ribs; they lift the ribs to help breathe in, especially during effort. Official name: External intercostal muscles [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=thorax&select=external_intercostals&side=r) Opens in the Durgical app, no sign-up needed. ## What it is Muscles between the ribs with fibres running down and forward. ## What it does Lift the ribs to help breathe in, especially when breathing hard. ## Key points - Outermost of the three intercostal layers; fibres run down and forward like hands in the front pockets, the same direction as the [external oblique](https://durgical.com/en/anatomy/external-abdominal-oblique-muscle/) - They run from the rib tubercles behind to the costochondral junctions in front; between the cartilages they are replaced by the external intercostal membrane - Inspiration: they raise the upper [ribs](https://durgical.com/en/anatomy/ribs/) and [sternum](https://durgical.com/en/anatomy/sternum/) (pump-handle, more front-to-back depth) and the lower ribs (bucket-handle, more width) ## Key facts **Origin** Inferior border of rib above **Insertion** Superior border of rib below; fibers run down and forward; replaced in front by external intercostal membrane **Action** Elevate ribs in inspiration; support intercostal space **Nerve** [Intercostal nerves](https://durgical.com/en/anatomy/intercostal-nerves/) (T1–T11) **Blood supply** Posterior and anterior intercostal arteries ## Relations **Superficial** [Pectoralis major](https://durgical.com/en/anatomy/pectoralis-major-muscle/) and minor, [serratus anterior](https://durgical.com/en/anatomy/serratus-anterior/), [latissimus dorsi](https://durgical.com/en/anatomy/latissimus-dorsi-muscle/) and the back muscles, depending on the level **Deep** [Internal intercostals](https://durgical.com/en/anatomy/internal-intercostal-muscles/), whose fibres cross theirs at right angles; the intercostal neurovascular bundle lies deeper still, under the internal layer **Above** Lower border of the rib above, from which they arise **Below** Upper border of the rib below, where they insert ## How to find it Not felt as a separate muscle: the intercostal spaces are palpated between the ribs, best on the lateral [chest](https://durgical.com/en/anatomy/region/chest/) wall. On ultrasound with the probe across two ribs, the three muscle layers lie between the rib shadows, with the bright pleural line beneath. ## Examination - Chest expansion: hands on the lower ribs with the thumbs meeting at the midline; reduced or asymmetric movement on deep inspiration points to a problem on that side of the wall, [pleura](https://durgical.com/en/anatomy/pleura/) or lung - Inspection for intercostal retractions: the spaces drawing in on inspiration signal increased work of breathing, a sign seen early in children ## On imaging On CT and MRI the three intercostal layers look like one thin muscle band between the ribs. Ultrasound with a linear probe across a space shows the layers between the rib shadows, above the bright pleural line: the view used to guide chest-wall blocks. After trauma or thoracotomy, CT shows lung herniating through a torn intercostal space. ## Clinical notes - Every needle or drain through the chest wall crosses all three intercostal layers, then the endothoracic fascia and the parietal pleura - Paralysis of the intercostal muscles (high [spinal cord](https://durgical.com/en/anatomy/spinal-cord/) injury) leaves the [diaphragm](https://durgical.com/en/anatomy/diaphragm/) to do the breathing, and the chest wall may draw in on inspiration ## Development Like the other intercostal layers, they come from the ventral extensions of the thoracic myotomes that grow round with the ribs; in the chest these stay separate segments, each with its own intercostal nerve, while over the [abdomen](https://durgical.com/en/anatomy/region/abdomen/) they fuse into the flat muscle sheets. ## Memory aid External intercostals = hands in the front pockets (down and forward); internal intercostals run at right angles to them. ## Related conditions - [Asthma](https://durgical.com/en/conditions/asthma/) - [Rib fractures](https://durgical.com/en/conditions/rib-fractures/) - [Flail chest](https://durgical.com/en/conditions/flail-chest/) ## Test yourself Think of the answer, then tap the question to see it. ## In which direction do the fibres of the external intercostal muscles run? Down and forward, like hands in the front pockets: the same direction as the external oblique. ## What is the action of the external intercostal muscles? They raise the ribs in inspiration: the upper ribs and sternum (pump-handle, more front-to-back depth) and the lower ribs (bucket-handle, more width). ## What replaces the external intercostal muscles in front, between the costal cartilages? The external intercostal membrane; the muscles run from the rib tubercles behind to the costochondral junctions in front. ## What nerves supply the external intercostal muscles? The intercostal nerves (T1–T11). [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/external-intercostal-muscles/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** musculi intercostales externi TA2 2311 **Official Spanish (DeCS)** Músculos intercostales externos DeCS D007366 **English (TA2)** External intercostal muscles ## Related - [Intercostal nerves](https://durgical.com/en/anatomy/intercostal-nerves/) - [Internal thoracic artery](https://durgical.com/en/anatomy/internal-thoracic-artery/) - [Posterior intercostal arteries](https://durgical.com/en/anatomy/posterior-intercostal-arteries/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=22524&filter=ths_termall&q=M%C3%BAsculos%20Intercostales); [Anatomy, Thorax, Wall Movements](https://www.ncbi.nlm.nih.gov/books/NBK526023/); [Anatomy, Thoracotomy and the Collateral Intercostal Neurovascular Bundle](https://www.ncbi.nlm.nih.gov/books/NBK544368/); Anatomy of the Human Body (20th ed.): Development of the Muscles (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain. ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/external-intercostal-muscles/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/external-intercostal-muscles/