Human Anatomy Vol 1

THORAX

and four coccygeal. In the thoracic, lumbar and sacral
regions, the number of vertebrae corresponds to the
number of spinal nerves, each nerve lying below the
corresponding vertebra. In the cervical region, there are
eight nerves, the upper seven lying above the
corresponding vertebrae and the eighth below the

seventh vertebra. In the coccygeal region, there is only

one coccygeal nerve.

Sometimes the vertebrae are also grouped according

to their mobility. The movable or true vertebrae include

the seven cervical, twelve thoracic and five lumbar

vertebrae, making a total of 24. Twelve thoracic verte-

brae have ribs attached to them. The fixed vertebrae

include those of the sacrum and coccyx.

The length of the spine is about^70 cm in males and

about 60 cm in females. The intervertebral discs

contribute one-fifth of the length of the vertebral

column.

As a result of variations in the width of the vertebrae,

the vertebral column can be said to be made up of four

pyramids (Fig. 13.16a). This arrangement has a

functional bearing. The narrowing of the vertebral

column at the level of the disc between fourth thoracic

and fifth thoracic vertebrae is partly compensated for

by the transmission of weight to the lower thoracic

region through the sternum and ribs.

Culvolures

In Sogf I Plans

I Primary curaes are present at birth due to the shape

of the vertebral bodies. The primary curves are

thoracic and sacral, both of which are concave

forwards.

2 Secondary curres are postural and are mainly due to

the shape of the intervertebral disc. The secondary

or compensatory curves are cervical and lumbar,

both of which are convex forwards. The cervical

curve appears during four to five months after birth

when the infant starts supporting its head: The

lumbar curve appears during twelve to eighteen

months when the child assurnes the upright posture

(Figs 13.16b and c).

Disc between C7 and T1

Disc between T4 and T5

FThoracic

Disc between L5 and S'1 tsSacral

Figs 13.16a to c: (a) Scheme to show that the vertebral column is divisible into a number of pyramidal segments, (b) primary

curves, and (c) secondary curues

Cervical

Lumbar

Fig. 13.14: Sternal puncture for bone marrow biopsy

(a) Funnel chest, and (b) pigeon chest