Human Anatomy, Part 2 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2008

Special Part
Peripheral Nervous System, systema nervosum periphericum — General Overview
Spinal Nerves — Intercostal Nerves

The Anterior branches of the Thoracic nerves are called intercostal nerves because they lie within the intercostal spaces (Fig. 196). The twelfth nerve runs below the corresponding rib, which is why its more precise name is the subcostal nerve, nervus subcostalis. The upper six pairs of intercostal nerves reach the Sternum. The lower six emerge from the intercostal spaces and enter the cleft between the internal oblique and transverse Abdominal Muscles. They reach the rectus abdominis Muscle by passing through its sheath. The subcostal nerve terminates in the lower part of the rectus abdominis and pyramidalis muscles. The intercostal nerves innervate all ventral muscles in the walls of the thoracic and abdominal cavities, as well as muscles of ventral origin on the back, namely mm. serrati posteriores superiores et inferiores, levatores costarum. They also contribute to the Innervation of the Pleura and Peritoneum. Along its course, each intercostal nerve gives off a lateral cutaneous branch, ramus cutaneus lateralis, and an anterior cutaneous branch, ramus cutaneus anterior. According to their origin, these branches are referred to as thoracic or abdominal. Each lateral branch divides into anterior and posterior parts, while each anterior branch divides into medial and lateral parts. They innervate the Skin of the trunk while maintaining a segmental pattern, with the innervation zone of each nerve appearing as a band-like strip.

Class="center">

Fig. 196. Intercostal nerves, nervi intercostales (schematic diagram)

The fourth through sixth intercostal nerves innervate the mammary gland. Their lateral cutaneous branches give rise to the lateral mammary branches, rami mammarii laterales, and the anterior cutaneous branches give rise to the medial mammary branches, rami mammarii mediales.