In smooth muscle cells, sarcomeres and regular striated Z discs are absent. Instead, actin thin filaments and intermediate filaments (desmin or vimentin) attach to protein-rich dense bodies (dense bands) scattered throughout the cytoplasm and along the sarcolemma. Dense bodies contain $\alpha$-actinin and serve the identical anchoring function as Z lines of skeletal muscle.

Option breakdown:

• Dense bodies are electron-dense structures that anchor actin thin filaments in smooth muscle, analogous to Z discs.
• Caveolae are small, flask-like plasma membrane invaginations involved in calcium entry, analogous to T-tubules.
• M line is the central line in the A band of striated muscle sarcomeres where thick filaments are cross-linked.
• Bachman's bundle is an interatrial conduction tract in the heart.

Statement (I) is correct: A right shift in the oxygen-hemoglobin dissociation curve (Bohr effect, induced by increased $H^+$, temperature, $p\text{CO}_2$, or 2,3-DPG) means that at any given $p\text{O}_2$, hemoglobin saturation is lower, signifying a decreased affinity for oxygen and facilitating oxygen release to metabolizing tissues.
Statement (II) is correct: In the rumen, microbial fermentation generates large volumes of gas consisting of approximately $60 - 65\%\text{ CO}_2$, $30 - 35\%\text{ CH}_4$, and minor amounts of nitrogen ($7\%$), hydrogen, and hydrogen sulfide. Thus, $\text{CO}_2$ is indeed the principal gas produced by percentage.

Option breakdown:

• Both Statement (I) and Statement (II) are physiologically accurate.
• Neither statement is incorrect.
• Statement (II) is correct.
• Statement (I) is correct.

Option analysis:
(A) In pigs, the esophageal tunica muscularis contains striated muscle only in the cranial one-third, transitioning to smooth muscle in the caudal two-thirds (unlike horses where it is striated in the cranial two-thirds, or ruminants/dogs where it is entirely striated).