Final answer:
It is true that a rabbit's chest cavity is very small, designed to house their respiratory and cardiovascular systems efficiently. The thoracic cavity plays a crucial role in respiration by changing size during inhalation and exhalation, while the pleural cavity within it contains the lungs and is not air-filled but may contain pleural fluid.
Step-by-step explanation:
The statement that a rabbit's chest cavity is very small is True. Rabbits, like many other small mammals, have a compact thoracic cavity to accommodate their respiratory and cardiovascular systems. While the chest cavity of a rabbit may be small, it's important to note that in mammals, the size of the thoracic cavity can change, particularly during respiration. When mammals inhale, the thoracic cavity expands, and during exhalation, it contracts. Inhalation involves contracting the diaphragm and intercostal muscles to create a negative pressure in the lungs relative to the outside environment, thus allowing air to enter the lungs.
The pleural cavity, which envelopes the lungs, is indeed part of the thoracic cavity, not to be mistaken with the abdominal or dorsal cavities. As for body cavities, they are not filled with air by default; rather, they may contain organs, and in the case of the pleural cavity, a small amount of pleural fluid to reduce friction during lung expansion. The thoracic cavity is protected by the rib cage, which includes the lower ribs for additional protection. This structural arrangement allows for the efficient functioning of the mammalian respiratory system which is summarized in conception by the passage of air through the nasal cavities, pharynx, trachea, bronchi, and into the alveoli of the lungs.