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Midaxillary Line · What Is It, Location, Function, and More
Published: Nov 06, 2025
Author: Alyssa Haag, MD•
Editor: Ahaana Singh•
Editor: Lisa Miklush, PhD, RN, CNS•
Editor: Kelsey LaFayette, DNP, ARNP, FNP-C
Illustrator: Aileen Lin
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What is the midaxillary line?
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Where is the midaxillary line located?
The midaxillary line originates in the axilla, or armpit, and passes vertically downwards. It is located between the anterior axillary line (i.e., front of the armpit) and the posterior axillary line (i.e., back of the armpit).
Within the armpit, the axillary line is located between the anterior axillary fold, formed by the muscles of the chest (i.e., pectoralis), and the posterior axillary fold, formed by two major muscles of the upper back, the latissimus dorsi and teres major. From there, it passes over the lateral thoracic wall and continues down the flank of the abdomen. In thin individuals, it runs just lateral to the midclavicular line and anterior to the scapular line.
What is the function of the midaxillary line?
The midaxillary line functions as a reference point for a number of procedures, including thoracentesis, paracentesis, and placement of electrocardiogram (ECG) leads. It is also used as a landmark for lung auscultation, determining the size of the liver, and kidney palpation. Finally, it’s used as a reference in ultrasound, chest X-rays, CT, and thoracic MRI as it divides the anterior, lateral, and posterior chest walls.
What are the most important facts to know about the midaxillary line?
The midaxillary line is an imaginary line that clinicians use as a reference point during a variety of procedures, such as a thoracentesis, paracentesis or an ECG. It’s also used to locate the base of the lungs, assess the size of the liver, and palpate the kidneys. The midaxillary lines goes from the armpit downwards through the torso and abdomen, dividing the body into its anterior and posterior halves.
Key Takeaways
Definition | The midaxillary line is an imaginary line running through an individual’s torso and abdomen, separating the body into the anterior and posterior halves. |
Location | - Originates in the axilla (armpit) - Passes vertically downwards - Passes over the lateral thoracic wall - Continues down the flank of the abdomen - Between the anterior axillary line (front of the armpit) and the posterior axillary line (back of the armpit) |
Function | - Reference point for procedures - Placement of electrocardiogram (ECG) leads - Landmark for: - Determining liver size - Imaging - Describe location of findings |
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