Once the epidermis removed (SKIN), the superficial adipose tissue (SAT) and deep adipose tissue (DAT) appear, separated by the fascia superficialis (FS)
Numerous authors describe it as comprising “fatty lobules”  or being “more or less impregnated with fat” [15, 24], while the most common nomenclature define the FS as including all the adipose which accompanies it . Lockwood  proposed to include the adipose layers in the term superficial fascial system (SFS). We will use Lancerotto’s  and Stecco’s  definition of the FS, that is to say, the FS refers to the membranous layer within the SFS only.
Composition and Location of the FS
Additional fibrous septums arise from the FS and form a three-dimensional mesh of transversal or oblique interlinking through the SAT and DAT. This network forms a honeycomb-like structure [28, 85] on which are attached the fatty lobules of the SAT and DAT. In the SAT, this network of septae is called retinacula cutis superficialis.
The collagen fibres of the FS are associated with elastin fibres that provide a great deformability to the fibro-elastic structure [21, 27]. The FS appears as well-defined, continuous and well-organised membrane or layer, of aspect predominantly membranous, with irregular islands of fat cells. Microscopically, it appears lamellar  or honey-comb-like [28, 85].
The mechanical roles of the FS are to cover, maintain and shape the fat of the trunk, and to connect the skin to the underlying structures while allowing sliding motion of soft tissues to occur with movement.
Furthermore, the fatty lobules of the FS ensure a mechanical protection to compression. The fatty lobules provide a resilience to compression that guaranties the protection of the underlying structures and the restitution of the initial form [27, 28].
In addition, some skeletal muscles attach only to the superficial fascia, such as the platysma muscle or the muscles of facial expressions that enable humans to smile, frown and cry .
Fascia Profundis (FP)
It is found in the literature by the name of deep fascia, thoracolumbar fascia [23, 31, 32], lumbodorsal fascia , tendon of the latissimus dorsi , or lumbar aponeurosis or fascia [26, 33–35]. It is described by Gray  as being made up of the lumbodorsal fascia, the lumbar aponeurosis and the vertebral fascia. Its close relationship with the muscles and the bones justifies that it is described as a “false aponeurosis” or “tendinous membrane” by Rouviere  and of “aponeurosis of the latissimus dorsi” by Cunningham .
Depending on the nature of its constitution and on where it is situated on the trunk, it will act as a means of docking for the contractile fibres on the bones, or act like a flexible sheath or like a rigid shell. The posterior layer and the middle layer, together with the postero-lateral region of the vertebral column, constitute an “osteofascial” compartment  that encloses the muscle group called erector spinae.
In the sacral region, below the level of L5, the fascia profundis, or thoracolumbar fascia, is a thick aponeurotic structure which attaches to the sacrum and laterally to the posterior iliac spines.
It comprises the aponeurosis of the Multifidus (M), L and IC muscles, as well as the aponeurosis of the latissimus dorsi. It is called by some authors the thoracolumbar composite (TLC).
Cranially to L5, the fascia profundis splits into three layers: the posterior layer (PLF), the middle layer (MLF) and the anterior layer (ALF).
Posterior Layer of the Fascia Profundis, Lumbosacral Region
The posterior layer of the fascia profundis (PLF) appears as a large, pearly white membranous sheet—a colour that is characteristic of this tissue. It is a dense, fibrous connective tissue. The fibres are parallel to one another within the matrix. Their orientation is oblique, cephalic or lateral.
The PLF is made up of the aponeurosis of the latissimus dorsi (LD), the aponeurosis of the serratus posterior inferior (SPi) and the posterior aponeurosis of the extensors (L+IC).
The aponeurosis of the latissimus dorsi (LD) and of some of the extensors (L+IC) emerge from the thoracolumbar composite (TLC) of the sacral region, and they define two layers or laminae:
The posterior aponeurosis of the LD and the aponeurosis of the SPi become the superior lamina of the PLF (sPLF) . It allows the insertion of the contractile fibres of the latissimus dorsi. The insertion roughly follows a line, starting between the median third, the posterior third of the iliac crest and the spinous process of T7.
The anterior aponeurosis of the LD and of the aponeurosis of the SPi, as well as the posterior part of the retinacular sheath that surrounds the paraspinal muscles (L+IC) becomes the deep lamina of the PLF (dPLF) .
Middle Layer of the Fascia Profundis, Lumbosacral Region
The aponeurosis of the QL and of the M, L and IC muscles separate from the thoracolumbar composite (TLC) of the sacral region. The middle layer of the PLF is made up of the anterior fascia of the M muscle, the posterior fascia of the QL, and the aponeurosis of the transversus abdominis (Tra) and internal oblique (IO).
The middle layer of the PLF is located in the plane of the costiform processes of the lumbar vertebrae.
Cephalically, it inserts on the inferior edge of the 12th rib and on the lumbo-costal ligament ; however this information varies depending on the authors.
At the L2 level, the middle layer will merge with the anterior layer. We will refer to the resulting layer as the anterior layer. The term “middle layer” therefore only exists in the lower lumbar region and in the cervical region.
Anterior Layer of the Fascia Profundis, Lumbosacral Region
From its differentiation with the TLC and up to the level of L2, the anterior layer of the PLF is made up of the anterior sheath of the QL muscle and extends laterally with the sheath of the psoas muscle (P), . Going cranially from L2, the middle layer merges with the anterior layer that is then made up of the anterior fascia of the multifidus muscles (M), and the surrounding sheath (anterior and posterior) of the QL [24, 36, 37].
The anterior layer is not taken into account identically by all the authors that can describe two or three layers to the fascia profundis in the lumbar region. Authors describing two layers do not include this anterior layer and refer to it as the transversalis fascia .
It inserts caudally on the superior edge of the iliolumbar ligament and on the iliac crest . The cephalic insertion of the deep layer varies according to authors. It is described as being on the arcuate ligament  or the lateral arcuate ligament (lateral lumbocostal arch) or medial arcuate ligament (medial lumbocostal arch) . Medially, it merges with the fascia iliaca, and with the sheath of the psoas muscle [20, 24] and inserts on the costiform processes of the lumbar vertebrae, laterally and posteriorly to the fascia iliaca . Its lateral insertion is on the lateral raphe.
The Lateral Raphe
The lateral raphe is made up of the merging of the posterior, middle and anterior layers, laterally to the QL muscle. It extends antero-laterally via the connective sheaths of the transversus abdominis (TA) and internal oblique (IO) abdominal muscles.
In the thoracic region , the fascia profundis consists of the posterior and anterior layers of the lumbosacral region. In between them, an additional fibrous element separates the extensors (L+IC+S) from (M+R): the intermediate layer.
Posterior Layer of the Fascia Profundis, Thoracic Region
In the thoracic region, the superficial lamina of the posterior layer (sPLF) covers the inferior fibres of the trapezius muscle (T). It is made up of the posterior aspect of the sheath of the trapezius muscle and therefore inserts on the spinous processes of the lower vertebrae (Fig. 5).
the anterior sheath of the rhomboid muscle (Rh) , then also includes the anterior sheath of the levator scapulae (LS) and of the serratus posterior inferior (SPi) and superior (SPs) (in continuity with this of the LD and SPi).
the posterior sheath of the spinalis muscle (in addition to this of the L+IC) then also includes this of the splenius muscle (Sp).
The Deep Lamina of the Posterior Layer of the Facia Profundis in the Thoracic Region
This connective layer is visible underneath the DL in the thoracic region . It contains thin and spaced-out pearl white fibres, the density of which varies according to the spinal level and the individual.
Aponeurosis of the serratus posterior muscle 
Dorsal fascia 
The generally admitted inferior spinal insertions globally correspond to the insertion of the serratus posterior inferior (SPi) . Its superior insertion is controversial. According to some authors [20, 21, 39, 42] it links the superior edge of the SPi to the inferior edge of the serratus posterior superior (SPs), which justifies the denomination of (intermediary) aponeurosis of the serratus.
Its close links with the abdominal muscles internal oblique and transversus seem to allow the transmission of the force that they develop to participate in the extension of the spine .
Intermediate Layer of the Fascia Profundis, Thoracic Region
Within the erector spinae or paraspinal muscles compartment, the intermediate layer is not a perfectly identified real layer but a sliding plane between more superficial longitudinal muscles (L + IC + E) and deepest muscles (M + R + Ssp).
Anterior Layer of the Fascia Profundis, Thoracic Region
The anterior layer of the fascia profundis does not have major changes in the thoracic region compared to the lumbosacral region. In the thoracic region, the anterior layer is in continuity with the extension of the sheath of the QL.
Posterior Layer of the Fascia Profundis, Cervico-Cranial Region
In the cervico-cranial region, the superficial lamina of the posterior layer (sPLF) is in continuity with the thoracic region and is therefore made up of the posterior aspect of the sheath of the trapezius muscle.
Cranially, from the upper nuchal line, it merges with the connective sheath of the skull.
LD wraps the latissimus dorsi in the thoracic region. In the cervico-cranial region, this same layer wraps the trapezius. It forms the superficial blade of the nuchal fascia and merges, from the superior nuchal line, with the connective sheath of the skull.
Intermediate Layer of the Fascia Profundis, Cranio-Cervical Region
The sheaths of the iliocostalis cervicis and longissimus cervicis muscles reach the transverse processes of the cervical vertebrae from C2.
The sheath of the longissimus capitis muscle becomes one with the connective sheaths of the skull from the mastoid process.
Middle Layer of the Fascia Profundis, Cranio-Cervical Region
At the T4 level, the middle layer emerges from the anterior layer. It is made up of the anterior fascia of the M+SSp and the posterior fascia of the Lcol+Lcap.
Anterior Layer of the Fascia Profundis, Cranio-Cervical Region
The sheaths of the scalene musles (Sc) insert on the superior edge of the first two ribs, and on the cervical vertebrae on their costiform process (anterior tubercle) and transverse process (posterior tubercle).
The sheaths of the suboccipital muscles reach the connective sheath of the skull from the inferior nuchal line.
The connective tissues of the back compose an envelope that individualises anatomical structures. Being continuous, this envelope homogenises and links the different anatomical structures. It has therefore a fundamental role in providing nervous information. Each of the layers that composes the connective tissues of the back has a specific organisation, constitution, appearance, function and relation. In consequence, their innervation is also variable and specific .
This informative function is insured by the sensitive information which remains not well-known in its distribution and function. It appears difficult to study with precision the sensitive innervation of the connective tissues, since they can have ramifications in the tissue as well as in the muscles or the skin. There are four types of sensory fibres in the connective tissues of the back that originate from different sensory receptors. These receptors differ in size, configuration, organisation, form and density. They are not specific to this region and are found throughout the whole body.
Sensory innervation is essential from the first weeks of the embryological development , and connective tissues have an essential role in the organisation and formation of the nerve fibres and of the muscles .
We will consider the sheath of the muscles as being part of their aponeurosis. All these aponeuroses compose the thoracolumbar fascia described above. This part will focus on the sensory innervation of the thoracolumbar fascia, the nervous endings of which are located within the muscle sheaths and aponeurosis. This description is not limited to the TLF and is applicable to the connective tissues in general.
Fibres and Receptors
The thoracolumbar fascia is innervated by the dorsal ramus of the spinal nerve [52–54]. The dorsal ramus has myelinated motor fibres (Aα, Aβ and Aγ), unmyelinated vasomotor fibres (C) and sensory fibres.
There are 4 types of sensory fibres, carrying information from the endings located in the muscle sheaths and aponeuroses to the dorsal horn of the spinal cord.
Sensory Fibre Types Found in the Connective Tissues of the Back
Type I sensory fibres have the largest diameter (12–20 μm) and are distributed in two sub-groups: type Ia sensory fibres that originate as annulospiral endings in muscle spindles, and type Ib sensory fibres that originate as Golgi tendon organs, Meissner corpuscles or Merkel corpuscles. They have the thickest myelin sheath and have therefore the highest conduction velocity (79–114 m/s) .