The four cervical muscle groups 
The deep muscles are pure intrinsic muscles.
Longus colli is an anterior intrinsic muscle of the lower cervical spine.
Para-median longitudinal deep fascicle extending from the body of C2 to that of T3,
Ascending upper oblique fascicle extending from the transverse processes of C3–C6 to the anterior tubercle of the atlas,
Descending lower oblique fascicle which extends from the transverse processes of C4–C7 to the bodies of T2 and T3.
These three fascicles create a diamond construct in which the bodies and discs of the lower cervical spine are inscribed. Longus colli is a flexor which flattens the cervical lordosis. It also has a stabilizing function to which we shall return.
The intertransversarius is a muscle that extends throughout the spine and is considered as an intrinsic lateral muscle.
The Transversarius Spinalis
The transversarius spinalis extends along the entire length of the column; it is a posterior intrinsic muscle divided into three layers: semi-spinous fascicles, long fascicles (multifidus), and short fascicles (rotatores).
The Peripheral Muscles
These are totally extrinsic muscles.
The supra- and infrahyoid muscles are anterior extrinsics.
The Sternocleidomastoid (SCM)
The Intermediate Muscles Extending Upwards
These are intrinsic muscles with proximal insertion on the base of the skull and distal insertion on the upper cervical spine.
The longus capitis which is positioned between the basilar process of the occiput and the anterior tuberculum of C3–C6.
The rectus capitis anterior located between the anterior limit of the occipital foramen and the lateral mass of the atlas.
The rectus capitis lateralis, parallel to the preceding one.
These three muscles are flexors and homolateral rotators.
The rectus capitis posterior major positioned between the inferior nuchal line of the occiput and the axis spinous process; it extends and inclines the head but has no real rotatory action.
The rectus capitis posterior minor, more medial, situated between the inferior nuchal line and the posterior ring of the atlas; it is an extensor.
The obliquus capitis inferior positioned between the transverse process of the atlas and the spinous process of the axis and which operates on the atlas, according to Kapandji  with the opposite obliquus capitis inferior acting as a pair of reins (Fig. 9). It controls homolateral rotation of the atlas.
The semispinalis capitis extending from the superior nuchal line to the transverse processes from C3 to T5 (Fig. 10).
The longissimus capitis which extends from the mastoid process to the transverse processes from C3 to T1.
The splenius capitis is inserted on the mastoid and the superior nuchal line and ends on the cervical spinous process. It is a powerful extensor and a homolateral rotator; it has in this movement a synergistic action with the controlateral SCM.
The Intermediate Muscles Extending Downwards
These are rather extrinsic muscles with a proximal insertion on the cervical spine but distal insertion at a distance on the thoracic spine, the ribs, or the scapula.
The scalenus anterior which extends from the anterior tubercle of the transverse processes from C3 to C6 to the upper surface of the first rib.
The scalenus medius which extends from the edge of the transverse process gutters of C2–C7 and ends on the same first rib behind the subclavian artery.
The scalenus posterior that extends from the posterior transverse tubercle of C4–C6 and ends on the second rib.
Besides their respiratory role, these muscles are flexors and lead to a homolateral inclination with contralateral rotation.
The Longissimus Cervicis
It extends from the transverse processes of the last four cervical vertebrae to those of the first five thoracic vertebrae; it is a powerful extensor.
The Ilio-Costalis (Fig. 10)
It has nearly the same origin as the preceding muscle; more lateral, it ends on the posterior arch of the first pair of ribs.
It extends between the spinous processes of C2 to C7 and participates in the constitution of the star-like formation of muscles around the spinous process of C2; we have shown only the cranial insertions in Fig. 8.
The Splenius Cervicis
It extends from the transverse processes of C1 to C3 to the spinous processes of the first five thoracic vertebrae; it is a direct extensor.
The Levator Scapulae
It is inserted on the tip of the transverse processes of the first four cervical vertebrae and after a tortuous path joins the superior medial angle of the scapula; if the scapula is fixed, it causes a homolateral extension-inclination.
The posterior or dorsal group which will extends inferiorly towards the lumbo-sacral junction.
The lateral group with the psoas and the quadratus lumborum.
Finally, the anterior or ventral group with the muscles of the abdominal wall.
Posterior Muscle Group
The Deep Plane
The transversus spinosus that exists at the cervical level is situated, according to Trolard, between the tip of the transverse process and the spinous processes or the laminae of the four overlying vertebrae. They are therefore muscular rafters (like the supports of a roof) which is commonly called the multifidus. More laterally and more superficially, we find the epi-spinalis of the thorax and the semi-spinous. The latter is purely thoracic and is situated between the transverse processes of the thoracic vertebrae and the spinous processes of the lower cervical vertebrae.
The spinalis thoracis also exists in the neck. It is more superficial and extends from the lateral surfaces of spinous processes from the thoracic region to the upper lumbar region where it is very close to the multifidus.
The longissimus thoracis, which extends from the longissimus capitis and the longissimus cervicis, unites downwards with the ilio-costalis to constitute the lumbo-sacral common mass. It inserts into the accessory processes of the lumbar vertebrae, the transverse processes of the thoracic vertebrae, and the posterior arch of the ribs.
The ilio-costal inserts on the posterior arch of the ribs and on the iliac crest.
According to Kapandji , the third lumbar vertebra at the apex of the lumbar lordosis, horizontal in the sagittal plane, is a true muscular relay (Fig. 14) since it receives from superiorly the longissimus and epi-spinalis thoracis and from inferiorly, the multifidus. This muscular disposition is reminiscent of that of the muscles around the posterior arch of C2.
Functionally, these posterior deep muscles are extensors and have rather a stabilizing function as shown by their composition in type 1 fibers (slow) and type 2 fibers (fast). Jorgensen  and Bagnall  demonstrated that these muscles were more rich in slow fibers than the superficial posterior muscles. It is interesting to note that in degeneration (or natural aging) these deep posterior muscles degenerate first and are replaced by fat and this normally occurs, from caudad to cephalad, from the lumbo-sacral junction to the upper lumbar spine.
Finally, at the base, the ilio-costalis, longissimus, and multifidus, although constituting the lumbo-sacral common mass, are separated by cleavage planes containing fat tissue. The multifidus—longissimus space can easily be dissociated with a finger and thus we can easily reach the articular processes or the transverse processes (classic Wiltse approach ) (Fig. 15).
The Intermediate Plane
The serratus posterior inferior is inserted on the spinal processes of the last thoracic vertebrae and the first lumbar vertebrae and ends on the caudal margin of the last four ribs. These two muscles have a function in inspiration.
The Superficial Plane
It consists of the trapezius , the rhomboideus, the latissimus dorsi, which are mobilizers of both the spine and the scapular girdle.
Lateral Muscle Group
The ilio-psoas consists of three heads (small and large psoas and iliac). It is innervated by the femoral nerve and has an action of lateral bending-rotation of the hip. Its action on the vertebral column is discussed: its contraction causes a homolateral inclination and a contralateral rotation (Fig. 18). In the sagittal plane, it is a lordosing muscle with lumbo-sacral flexion, as shown in the diagram of Kapandji  (Fig. 19).
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