FIGURE 7.

Schematic depiction of the three components mapped to the muscle classes. (A) Map of the three nerve components to muscle classes. Primaxial muscle-innervating branches (purple) include the dorsal segmental branches to the supracostal and external oblique, the ventral segmental branches to the longus-transversus and deep costal muscles classes, and the primaxial anterior branch to the primaxial rectus class. The LCB (light green) also consists of a pair of the dorsal and ventral subbranches, accompanying the dorsal and ventral extramural branches (dark green) to the girdle and limb muscle classes. The intramural branch (blue) innervates the internal oblique, transversus, and rectus muscle classes, and no dorsal counterpart exists. (B) Diagram with the layer information. The terminal branches of the three-components run in different inter-muscular spaces: the primaxial anterior branch in the superficial inter-muscular space, the intramural branch in the deep inter-muscular space, and the extramural branch in the outside of the body wall. A basic building unit is created from the innervation pattern of the dorsal rami to the four subclasses of the intrinsic back muscles; one main branch sends muscle-innervating twigs to a parallel pair of muscles, and ends as one terminal sensory branch (broken lines). Note that the body wall is composed of the eight muscle layers.