Origin of Serratus posterior inferior.

• A. Nuchal ligament and spinous processes C7-T4
• B. Spinous processes of T11-L2
• C. Inferior borders of ribs 8-12
• D. Transverse processes of C1-C3

Answer: (B)

Serratus posterior inferior originates from the spinous processes of the lower thoracic and upper lumbar vertebrae, specifically around T11 to L2. From there the fibers run laterally and downward to reach the inferior borders of the lower ribs (commonly 8–12). This placement explains its role in depressing the ribs to assist with expiration, and its innervation comes from the thoracic ventral rami (intercostal nerves T9–T12).

The other details described fit different parts of the back musculature. The nuchal ligament and spinous processes from C7 to T4 are the origin story for serratus posterior superior, not the inferior muscle. The inferior borders of ribs 8–12 are the insertion, not the origin. Transverse processes of C1–C3 do not serve as the origin for Serratus posterior inferior.