The muscles of the back are divided into two groups, the extrinsic and the intrinsic muscles (mm. dorsi proprii), which are separated by the lamina posterior of the fascia thoracolumbalis. The superficial extrinsic muscles are considered muscles of the upper limb that have migrated to the back; these muscles are discussed in the Upper Limb, pp. 312–317.
Fig. 3.1 Superficial extrinsic muscles of the back
Posterior view. Removed: Mm. trapezius and latissimus dorsi (right). Revealed: Fascia thoracolumbalis. Note: The lamina posterior of the fascia thoracolumbalis is reinforced by the aponeurotic origin of the m. latissimus dorsi.
Fig. 3.2 Fascia thoracolumbalis
Transverse section, superior view. The mm. dorsi proprii are sequestered in an osseofibrous canal, formed by the fascia thoracolumbalis, the arcus vertebrarum, and the procc. spinosi and transversi of associated vertebrae. The fascia thoracolumbalis consists of a lamina poste rior and lamina media that unite at the lateral margin of the mm. dorsi proprii. In the neck, the lamina posterior blends with the fascia nuchae profunda, becoming continuous with the fascia cervicalis (lamina prevertebralis).
Fig. 3.3 Muscles in the nuchal region
Posterior view. Removed: Mm. trapezius, sternocleidomastoideus, splenius, and semispinalis (right). Revealed: Nuchal muscles (right).
Fig. 3.4 Short nuchal muscles
Posterior view. See Fig. 3.6. Three of the short nuchal muscles (m. obliquus capitis inferior, m. obliquus capitis superior and the m. rectus capitis posterior major) form the boundaries of the suboccipital triangle (region).
The extrinsic muscles of the back (mm. trapezius, latissimus dorsi, levator scapulae, and rhomboidei) are discussed in the Upper Limb, pp. 316–317. The m. serratus posterior, considered an intermediate extrinsic back muscle, has been included with the superficial intrinsic muscles in this unit.
Fig. 3.5 Musculi dorsi proprii
Posterior view. Sequential dissection of the fascia thoracolumbalis, superficial intrinsic muscles, intermediate intrinsic muscles, and deep intrinsic muscles of the back.
The mm. dorsi proprii are divided into superficial, intermediate, and deep layers. The mm. serrati posteriores are extrinsic back muscles, innervated by the rr. anteriores of nn. intercostales, not the rr. posteriores, which innervate the mm. dorsi proprii. They are included here as they are encountered in dissection of the back musculature.
Fig. 3.9 Intermediate mm. dorsi proprii, schematic
Right side, posterior view. These muscles are collectively known as the erector spinae.
The deep intrinsic back muscles are divided into two groups: mm. transversospinalis and deep segmental muscles. The mm. transversospinalis pass between the procc. transversi and spinosi of the vertebrae.
