Chest and Abdominal Wall

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Chapter 19 Chest and Abdominal Wall

Thoracic Ventral Spinal Rami

There are 12 pairs of thoracic ventral rami. The upper 11 lie between the ribs (intercostal nerves), and the twelfth lies below the last rib (subcostal nerve) (Figs 19.1, 19.2). Each is connected with the adjoining ganglion of the sympathetic trunk by grey and white rami communicantes; the grey ramus joins the nerve proximal to the point at which the white ramus leaves it. Intercostal nerves are distributed primarily to the thoracic and abdominal walls. The first two nerves supply fibres to the upper limb in addition to their thoracic branches, the next four supply only the thoracic wall and the lower five supply both thoracic and abdominal walls. The subcostal nerve is distributed to the abdominal wall and the gluteal skin. Communicating branches link the intercostal nerves posteriorly in the intercostal spaces, and the lower five nerves communicate freely in the abdominal wall.

Fig. 19.1 Course of a typical intercostal nerve. The muscular and collateral branches are not shown.

Fig. 19.2 Approximate segmental distribution of the cutaneous nerves on the front of the trunk. The contribution from the first thoracic spinal nerve is not shown, and the considerable overlap between adjacent segments is not indicated.

First to Sixth Thoracic Ventral Rami

The first thoracic ventral ramus divides unequally. A large branch ascends across the neck of the first rib, lateral to the superior intercostal artery, and enters the brachial plexus. The smaller branch is the first intercostal nerve; it runs in the first intercostal space and ends on the front of the chest as the first anterior cutaneous nerve of the thorax. It gives off a lateral cutaneous branch, which pierces the chest wall in front of the serratus anterior and supplies the axillary skin; it may communicate with the intercostobrachial nerve and sometimes joins the medial cutaneous nerve of the arm. The first thoracic ramus often receives a connecting ramus from the second, which ascends in front of the neck of the second rib.

The second to sixth thoracic ventral rami pass forward in their intercostal spaces below the intercostal vessels. At the back of the chest they lie between the pleura and external intercostal membranes, but in most of their course they run between the internal intercostals and the subcostals and innermost intercostals (see Fig. 19.2). Near the sternum, they cross anterior to the internal thoracic vessels and transversus thoracis; pierce the internal intercostals, external intercostal membranes and pectoralis major; and end as the anterior cutaneous nerves of the thorax, which supply the skin on the front of the thorax. The second anterior cutaneous nerve may be connected to the medial supraclavicular nerves of the cervical plexus; twigs from the sixth intercostal nerve supply abdominal skin in the upper part of the infrasternal angle.