Question

which muscle of respiration is indicated in the picture by the letter a?

internal intercostal
internal oblique
external intercostal
external oblique

Explanation:

Identify the anatomical structure labeled A

Using the Intercostal Muscles and Muscles of Respiration knowledge points

• The pointer labeled A points to the superficial muscle layer located between the ribs (intercostal spaces).
• The fibers of this muscle run obliquely downward and forward (anteriorly and inferiorly, like putting your hands in your pockets).
• This fiber direction and superficial position relative to the inner layers identify it as the external intercostal muscle.

Evaluate the multiple-choice options

Using the Muscles of Respiration knowledge point

• "Internal intercostal": Incorrect. These lie deep to the external intercostals, and their fibers run at right angles (downward and backward).
• "Internal oblique": Incorrect. This is an abdominal wall muscle, not located in the thoracic intercostal spaces.
• "External intercostal": Correct. This matches the superficial thoracic muscle layer labeled A.
• "External oblique": Incorrect. This is a superficial abdominal muscle, located inferior to the rib cage.

Answer:

• Internal intercostal
• Internal oblique
• External intercostal (Correct answer)
• External oblique