3 Musculature: Topographical Anatomy
3.1 The Back Muscles and Thoracolumbar Fascia
A The thoracolumbar fascia as a partition between the intrinsic and nonintrinsic back muscles
The trapezius muscle has been completely removed and the latissimus dorsi has been partially removed on the right side to reveal the thoracolumbar fascia. The superficial layer of the thoracolumbar fascia separates the intrinsic back muscles from the nonintrinsic muscles that have migrated to the back.
Note: The superficial layer of the thoracolumbar fascia is located close to the spinal column just beneath the skin, where it is heavily reinforced and serves as the origin for the extensive tendon of the latissimus dorsi. Lateral to the origin, the superficial layer is pushed beneath both the tendon and the muscle, thereby losing direct contact to the subcutaneous tissue. Along its entire width, medial to lateral, the superficial layer covers the intrinsic back muscles.
B Thoracolumbar fascia
a Transverse section through the neck at the level of the C6 vertebra, superior view.
b Transverse section through the posterior trunk wall at the level of the L3 vertebra (cauda equina removed), superior view.
The thoracolumbar fascia forms the lateral portion of an osseofibrous canal that encloses all of the intrinsic back muscles. In addition to the thoracolumbar fascia, this canal is formed by the vertebral arches and the spinous and costal processes of the associated vertebrae. The thoracolumbar fascia consists of a superficial and a deep layer, especially in the lumbar region; both layers unite at the lateral margin of the intrinsic back muscles. At the back of the neck, the superficial layer of the thoracolumbar fascia blends with the nuchal fascia (deep layer), becoming continuous with the prevertebral layer of the cervical fascia.
Note: According to the new anatomic nomenclature, the thoracolumbar fascia consists of three layers: What was previously the deep layer is now the middle layer (lamina media); the new deep layer is the fascia of the quadratus lumborum. The superficial layer remains unchanged.
3.2 The Intrinsic Back Muscles: Lateral and Medial Tracts
A Course of the thoracolumbar fascia
Posterior view. To reveal the thoracolumbar fascia, both shoulder girdles and the extrinsic back muscles have been removed (except for the serratus posterior superior and inferior and the aponeurotic origin of the latissimus dorsi on the right side).
B Lateral tract of the intrinsic back muscles
Posterior view. Portions of the superficial layer of the thoracolumbar fascia have been removed on the left side of the back to expose the lateral tract muscles (iliocostalis, longissimus, and splenius muscles). The levatores costarum and intertransversarii muscles, also part of the lateral tract, are covered here by the iliocostalis and longissimus muscles (see C and D).
Note that the thoracolumbar fascia on the back of the neck is continuous with the deep layer of the nuchal fascia.
C Medial tract of the intrinsic back muscles (portions of the lateral tract left in place)
Posterior view. The longissimus (except for longissimus capitis) and splenius muscles have been removed on the left side of the back, and the iliocostalis muscles have been removed on the right side (see D for the rotatores muscles).
Note the deep layer of the thoracolumbar fascia from which both the internal oblique and the transversus abdominis muscles originate (see D).
D Medial tract of the intrinsic back muscles (with the entire lateral tract removed)
Posterior view. The entire lateral tract (except for the intertransversarii and levatores costarum) has been removed, along with portions of the medial tract, to demonstrate the various individual muscles of the medial tract.
Note the origin of the transversus abdominis from the deep layer of the thoracolumbar fascia in the lumbar region (left side).
On the right side, the deep fascial layer and multifidus muscle have been removed to display the intertransversarii (lateral tract) and the quadratus lumborum (posterior [deep] abdominal muscle).
3.3 The Intrinsic Back Muscles: Short Nuchal Muscles
A Location of the short nuchal muscles (suboccipital muscles)
Nuchal region, posterior view. The suboccipital muscles in the strict sense are the short (deep) nuchal muscles that belong to the intrinsic back muscles (recti capitis posterior major and minor and obliquii capitis superior and inferior). They meet the criterion of being innervated by a posterior ramus—in this case the C1 posterior ramus, the suboccipital nerve. The recti capitis anterior and lateralis are not classified as intrinsic back muscles, despite their suboccipital location, because they are innervated by anterior rami. The short nuchal muscles lie within the thoracolumbar fascia deep at the back of the neck and course between the occiput and the first two cervical vertebrae. They act mainly on the craniovertebral joints (see p. 122) and support differentiated head movements (e.g., for fine adjustments of head position). The following muscles have been partially removed to reveal their location in the right nuchal region: trapezius, sternocleidomastoid, splenius capitis, and semispinalis capitis. An important landmark in the deep nuchal region is the spinous process of the axis.
B Course of the short nuchal muscles
Suboccipital region, posterior view. The rectus capitis posterior major and obliquus capitis superior muscles on the right side have been partially removed.
C Origin and insertion of the short nuchal muscles
Suboccipital region, posterior view. The colored areas indicate the origins (red) and insertions (blue) of the muscles.
3.4 The Thoracic Wall Muscles and Endothoracic Fascia
A Muscles of the thoracic wall
a Anterior view, b posterior view. Topographically, the intercostal, transversus thoracis (see Ba), and subcostal (see Bb) muscles are included in the category of thoracic wall muscles.
Note: The scalene muscles, which belong to the deep neck muscles topographically, are classified functionally as thoracic muscles owing to their involvement in thoracic breathing. Hence they are included in the drawings.
The diaphragm, also considered a thoracic muscle, is shown in Bc and on p. 176. The nonintrinsic back muscles are described on p. 146.
B Endothoracic fascia
a Posterior surface of the anterior thoracic wall segment removed in b.
b Posterior thoracic wall, anterior view (endothoracic fascia removed on the left side).
c Coronal section through the lateral thoracic wall and costodiaphragmatic recess.
The thoracic cavity is lined by a fascia-like layer of connective tissue, the endothoracic fascia. It lies between the deep muscles of the thoracic wall and the costal portion of the parietal pleura, to which it is firmly attached, and is analogous to the transversalis fascia of the abdominal cavity (a). The endothoracic fascia is thickened over the pleural apex to form the suprapleural membrane (Sibson’s fascia). The phrenicopleural fascia is the portion of the endothoracic fascia that connects the diaphragmatic part of the parietal pleura to the upper surface of the dia phragm (b). The costodiaphragmatic recess (c) between the chest wall and diaphragm is a potential space that enlarges on inspiration (during lowering of the diaphragm) to accommodate the expanding lung. The pleural space is the potential space located between the parietal/costal pleura and the visceral pleura, which directly invests the lung tissue.
3.5 Thoracoabdominal Junction: The Diaphragm
A The diaphragm, superior view
The diaphragm consists of three parts: costal, lumbar, and sternal. As the muscle that separates the thoracic and abdominal cavities, the diaphragm has characteristic apertures for the passage of the esophagus, inferior vena cava, and aorta (see Cb and Db).
B The diaphragm, inferior view
C Position and shape of the diaphragm, viewed from the left side
Midsagittal section demonstrating the right half of the body. The diaphragm is in an intermediate position at end-expiration.
a The apertures in the diaphragm are depicted at vertical positions corresponding to the following landmarks in the lower thoracic spine: caval opening = T 8 vertebral body, esophageal hiatus = T 10 vertebral body, aortic hiatus = T 12 vertebral body.
b The diaphragmatic apertures and the structures that they transmit (see p. 207).