The structure which does not contribute to the breathing in mammals is the Larynx.
The larynx, also known as the voice box, is responsible for producing sound and is involved in speech. While it plays a crucial role in vocalization, it does not directly contribute to the breathing process in mammals. Here's a breakdown of the other structures involved in breathing:
1. Diaphragm:
- The diaphragm is a domed-shaped muscle located at the base of the thoracic cavity.
- It separates the thoracic cavity from the abdominal cavity.
- During inhalation, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity, which allows the lungs to expand and fill with air.
2. Intercostal Muscles:
- The intercostal muscles are located between the ribs.
- They consist of external intercostal muscles and internal intercostal muscles.
- During inhalation, the external intercostal muscles contract, lifting the ribcage and expanding the chest cavity.
- During exhalation, the internal intercostal muscles contract, pulling the ribcage downward and decreasing the volume of the chest cavity.
3. Ribs:
- The ribs are long, curved bones that form the ribcage.
- They protect the vital organs in the thoracic cavity, including the lungs and heart.
- The ribs are attached to the spine at the back and the sternum (breastbone) at the front.
- They provide structural support to the chest and help in the expansion and contraction of the thoracic cavity during breathing.
In summary, while the diaphragm, intercostal muscles, and ribs are all involved in the breathing process in mammals, the larynx is primarily responsible for vocalization and does not directly contribute to the inhalation and exhalation of air.

Larynx is voice box which is responsible to produce sound.