Follow
the dissection manual closely for instructions on skinning the back and observation
of the superficial features of the back. Grant's manual should be referenced
throughout the entire dissection.
After skinning and
removing the superficial fascia, the superficial back muscles are visible. The
trapezius muscle originates from the external occipital protuberance, the
ligamentum nuchae, and the spinous processes of C7 and T1-T12.
The ligamentun nuchae is a strong supraspinous tendon that extends from the
occipital protuberance to C7.2. The trap. m. has fibers that run in several
directions:
Superior portion-
fibers run inferolaterally & insert into the lateral 1/3 of the clavicle
Middle portion-
fibers run transversly & insert on the acromion & spine of scapula
Inferior portion-
fibers run superolaterally and converge into an aponerosis near the medial
end of the spine of the scapula
The trap. m. needs to be reflected for access
to the deeper layers of muscle. After carefully cutting along the midline as
close to the origin as possible, you can reflect the trap m. superiorly, exposing
the underlying structures. You can now see the spinal
accessory nerve running vertically on the undersurface of the muscle. On
a closer view, you can see the
nerve as it runs from the sternocleidomastoid m. to its termination between
fibers of the trap. m.
The latissimus
dorsi m. arises from the thoracolumbar fascia of the lower back. Its superior
border extends laterally from the spinous processes of T6-7 while its most lateral
parts interdigitate with fibers of the external oblique inferior m. The fibers
of the muscle form a broad tendon which inserts into the intertubercular fossa
of the humerus.
The triangle
of auscultation is visible after removal of skin on the back. This is an
anatomical space that is used by physicians to listen to sounds produced by
the lungs and other thoracic organs.
The borders are:
Trapezius m.
Lat. dorsi m.
Vertebral border of the scapula &
rhomboid major m.
At this location,
ribs 6 and 7 and the intercostal space are free of overlying mm., making it
easier for auscultation.
FIG. 1-5 : RHOMBOIDEUS
& LEVATOR SCAPULA (back
to top)
After reflection of the trapezius and lat. dorsi
mm., the next layer of superficial muscles is exposed. This includes the rhomboid
major and minor muscles and the levator scapula muscle. The rhomboid minor
muscle originates from the spinous process of C7-T1 and ligamentum nuchae, and
inserts on the upper 1/3rd of the verterbral border of the scapula. The rhomboid
major muscle originates from the spinous process of T2-5 and inserts on the
lower 2/3rds of the verterbral border of the scapula. The levator scapula muscle
originates on the transverse processes of C1-4 and inserts onto the superior
angle of the scapula.
The intermediate muscle group
consists of the Serratus Posterior
Superior and Inferior mm. These muscles are paper thin therefore caution
must be used when dissecting these muscles. The serr.
post. inf. m. is seen upon reflection of the lat. dorsi m. from its origin
along the spine. It originates from the spinous processes of T11-L2 and inserts
on the inferior borders of ribs 8-12 near their angles.
The serr. post. sup. m. is
located deep to the rhomboid mm. This muscle is found after careful detachment
of the rhomboid mm. from their origin. The serr. post. sup. arises from the
ligamentum nuchae & spinous processes of C7-T3 and inserts onto the superior
borders of ribs 2-4.
FIG. 1-7
: SPLENIUS CAPITIS AND CERVICIS (back
to top)
After removal of the trap. m., splenius capitis
and cervicis mm. are exposed. The splenius
mm. originates at the spinous processes of C7-T3. Splenius capitis inserts
into the nuchal line on the occipital bone and the mastoid process of temporal
bone. Splenius cervicis inserts into the posterior tubercles of transverse process
of C1-C3(C4).
The first layer of deep muscles in the back consist of long
vertically oriented muscle bundles running down both sides of the back from
the occipital bone to the pelvis. The erector
spinae mm. include:
The spinalis
m. is a relatively thin mm. (about 2cm) that connects to the lumbar, thoracic,
and cervical spinous processes.
Capitis- originates on the transverse processes
of C7-T7 and articular process of C4-6. It inserts between the superior
and inferior nuchal lines on the occipital bone.
Cervicis- originates on the spinous processes
of C7-T2. It inserts onto the spinous processes of C2-3.
Thoracis- originates on the spinous processes of T11-L2.
It inserts on the spinous processes of T4-8.
After removal of the first deep layer of back
mm., the erector spinae, the Transversospinalis m. group can be dissected out.
Follow Grant's dissector manual carefully, as these mm. are difficult to dissect.
The semispinalis m. is comprised of three divisions.
Capitis-
originates on the transverse processes of C7-T6 and the articular processes
of C4-6. This m. inserts on the superior and inferior nuchal lines of the
occipital bone.
Cervicis- arises from the transverse processes
of T1-6 and articular processes of C4-7. It inserts into the spinous processes
of C2-5.
Thoracis-
originates on the transverse processes of T7-12 and inserts
on the spinous processes of C6-T4.
After reflecting the semispinalis m., the multifidus
m. can be dissected out. This muscle consists of many short bundles which
are the most prominent in the lumbar region.
Its many origins include:
the posterior aspect of the sacrum
PSIS
posterior sacroiliac ligament
mamillary processes of lumbar vertebrae
transverse processes of all thoracic vertebrae
articular processes of C4-7
Its insertion is into the spinous process of the
vertebrae TWO to FOUR LEVELS
ABOVE THE LEVEL OF ORIGIN.
The deepest layer of the transversospinalis m.
group is the rotatores m.
These mm. originate on the transverse process of one thoracic vertebrae and
insert on the base of the spinous process of the vertebrae ONE
to TWO LEVELS ABOVE THE LEVEL OF ORIGIN.
The levator
costorum mm. can be seen lateral to the transverse process of the vertebrae,
running inferolateral in between the ribs. The origin is the transverse process
of C7-T11. They insert between the tubercle and the angle on the outer surface
of the ribs below the vertebrae of origin.
The intertransversarii
mm. are deep back muscles that bend the spinal column laterally. They are
usually poorly developed in the thoracic region. The origin and insertions of
this muscle is between the transverse processes of cervical, throacic and lumbar
vertebrae.
JOINTS OF THE BACK
Although we will not show dissected joints of
the back, it is important to understand all relevant anatomical components.
Click here for labeled diagrams and descriptions
of the joints adapted from Grant's Atlas.
