4.1: Thorax: Body wall

Body wall

Wall of thorax and abdomen are one (only difference is ribs).

Skin is thick behind, thin in front, and tension lines run horizontally.

Subcutaneous tissue

Scarpa’s fascia (condensation of the fibrous septa of the subcut tissue into a membrane) allows subcutaneous fat (called Camper’s fascia) to slide on musculoaponeurotic tissues of trunk.

- disappears over upper thorax and midaxillary lines

- attaches to fascia lata below inguinal ligament.

- attaches to sides & body of pubic bone; continued over penis & scrotum as Colle’s fascia.

Blood supply

Intercostal and lumbar arteries ® flanks;

Internal thoracic, superior & inferior epigastric arteries ® ventral tissues.

Cutaneous branches from these ® fat & skin.

Venous return different: network of veins radiating away from umbilicus; below it ® long saphenous vein, above ® lateral thoracic ® axillary vein. (see Pl 239)

- some paraumbilical veins pass to ligamentum teres ® L portal vein (®Caput Medusae)

- longitudinal vein (thoracoepigastric) unites lateral thoracic vein and superficial epigastric, hence ® prominent in IVC obstruction

Lymphatics (169)

From skin ® follow veins (ie to axillary and superficial inguinal nodes)

Above umbilicus

Anterior lymphatics ® pectoral nodes (anterior axillary)

Posterior ® scapular nodes (posterior axillary)

Below umbilicus

Anterior ® medial superficial inguinal nodes

Posterior ® lateral superficial inguinal nodes

Cutaneous innervation (240)

Above 2^nd rib ® supraclavicular branches of cervical plexus

Below 2^nd rib

Ventral midline strip of skin by anterior terminal branches of T2 ® L1.

Lateral strip by lateral cutaneous branches T2-3 ® L1 (emerge in midclavicular line)

- lateral cutaneous branch of T12 and iliohypogastric descend over iliac crest to supply buttock

- ilioinguinal nerve has no lateral cutaneous branch (it is a collateral branch of iliohypogastric)

Posterior strip by posterior rami of spinal nerves; medial to T6, then lateral.

Morphology of body wall muscles

Segmentation of mesoderm ® trunk myotomes, dividing into dorsal and ventral parts supplied by posterior & anterior rami of spinal nerves.

Dorsal parts ® erector spinae.

Ventral parts ® three layers of body wall; neurovascular plane lying between middle & inner layers.

	Outer layer	Middle	Inner
Neck	Scalenus posterior	Scalenus medius	Scalenus anterior, longus capitis, longus cervicis
Thorax	External intercostals	Internal intercostals	Innermost intercostals, transversus thoracis & subcostals
Abdo	External oblique	Internal oblique	Transv abdominis, QL, levator ani

In midline the 3 layers fuse ® rectus abdominis in abdo, sternalis in chest (occasionally), straps in neck.