Human Anatomy Vol 1

BONES AND JOINTS OF THORAX

Time of

appearance

A cftrmeelfs

1 The anterior surface gives origin on either side to

the pectoralis major muscle (Fig. 13.9).

2 The lower part of the posterior surface gives origin

on either side to the sternocostalis muscle.

3 On the right side of the median plane, the posterior

surface is related to the anterior border of the right

lung and pleura. On the left side, the upper two

pieces of the body are related to the left lung and

pleura, and the lower two pieces to the pericardium

(Fig. 13.12).

4 Between the facets for articulation with the costal

cartilages, the lateral borders provide attachment to

the external intercostal membranes and to the

internal intercostal muscles (see Fig. 74.L).

Xiphoid Plocess

The xiphoid process is the smallest part of the sternum.

It is at first cartilaginous, but in the adult it becomes

ossified near its upper end. It varies greatly in shape

and may be bifid or perforated. It lies in the floor of the

epigastric fossa (Fig. 13.10).

Affcefrmemfs
1 The anterior surface provides insertion to the medial
fibres of the rectus abdominis, and to the
aponeuroses of the external and internal oblique
muscles of the abdomen.
2 Tlte posterior surface gives origin to the diaphragm.
It is related to the anterior surface of the liver.
3 The lateral borders of the xiphoid process give
attachment to the aponeuroses of the internal oblique
and transversus abdominis muscles.
4 The upper end forms a primary cartilaginous joint
with the body of the stemum.
5 The lower end affords attachment to the linea alba.

The sternum develops by fusion of two sternal plates

formed on either side of the midline. The fusion of

the two plates takes place in a craniocaudal direction.

Manubrium is ossified from 2 centers appearing

in 5th foetal month. First and second sternebrae

ossify from one center appearing in 5th foetal month.

Third and fourth sternebrae ossify from paired

centers which appear in 5th and 6th months. These

fuse with each other from below upwards during

puberty. Fusion is complete by 25 years of age. The

manubriosternal joint which is a secondary

cartilaginous joint usually persists throughout life.

The centre for the xiphoid process appears during

the third year or later. It fuses with the body at about

40 years (Figs 13.13a and b).

5th to 6th

fetal month

3rd year

(a) (b)

Figs 13.13a and b: Ossification of sternum

Trme of

unron

Remains

ununited

Between 17th

to 25th years

Soon after

puberty

Fusion at

about 40th

year

Bone marrow for examination is usually obtained

by manubriostemal puncture (Fig. 13. 14). It is done

in its upper half to prevent injury to arch of aorta

which lies behind its lower half.

The slight movements that take place at the

manubriosternal joint are essential for movements

of the ribs.

Lr the anomaly called'funnel chest', the sternum

is depressed (Fig. 13.15a).

In another anomaly called'pigeon chest', there is

forward projection of the sternum like the keel of

aboat, and flattening of the chest wall on either

side (Fig. 13.15b).

For cardiac slrrgery the manubrium and/or body

of sternum need to be splitted in midline and the

incision is closed with stainless steel wires.

Sternum is protected from injury by attachment

of elastic costal cartilages. Indirect violence may

Iead to fracture of sternum.

Non-fusion of the sternal plates causes ectopia

cordis, where the heart lies uncovered on the

surface. Partial fusion of the plates may lead to

the formation of sternal foramina, bifid xiphoid

process/ etc. (Fig. 13.9).

Veilebrol Column os o Whole

The vertebral column is also called the spine, the spinal

column, or back bone. It is the central axis of the body.

It supports the body weight and transmits it to the

ground through the lower limbs.

The vertebral column is made up of 33 vertebrae;

seven cervical, twelve thoracic, five lumbar, five sacral