Intercostal Artery:

Each intercostal space contain two anterior intercostal artery and one posterior intercostal artery. There are nine intercostal spaces anteriorly.

Anterior Intercostal Artery:

First six  intercostal artery arise from internal thoracic artery. Next three arise from muculophrenic artery.

Internal Thoracic Artery:

It arises from  first part of subclavian artery . It passes just lateral to sternum and ends at the sixth intercostal space by dividing into its sternal branches namely superior epigastric artery and musculophrenic artery. Superior epigastric artery enters the abdomen by passing through larry's space or foramen of morgagni. Larry's space is the space between the ziphoid and costal origin of diaphragm. Musculophrenic artery  pierces the diaphragm at the level of ninth costal cartilage.

Posterior Intercostal Artery:

There are eleven posterior intercostal spaces. Each space contain one posterior intercostal artery. The first two posterior intercostal artery are branches from superior intercostal artery which in turn is a branch from costocervical trunk. Costocervical trunk is a branch from second part of subclavian artery.

left  side subclavian artery is a branch from arch of aorta whereas the right side is a branch from brachiocephalic artery.

The remaining posterior intercostal artery is a branch from descending thoracic aorta.

Branches of posterior intercostal artery:

Right sided bronchial artery arise from third posterior intercostal artery.

Descending thoracic aorta:

It is the continuation of arch of aorta which starts at the level of T4-T5 i.e. at the level of sternal angle of  louis. Embryologically it is derived from left fourt arch artery.

It passes through posterior mediastinum.

Branches:

1.  Third to eleventh posterior intercostal artery

2. Subcostal artery

3. Left bronchial artery.