The Costal groove is a groove between the ridge of the internal surface of the rib

Rib

In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...

 and the inferior border. It contains the intercostal vessels

Intercostal vessels

Intercostal vessels can refer to:* arteries** Posterior intercostal arteries** Highest intercostal artery** Anterior intercostal branches of internal thoracic artery* veins** Supreme intercostal vein** Superior intercostal vein...

 and intercostal nerve.
In herpetology

Herpetology

Herpetology is the branch of zoology concerned with the study of amphibians and reptiles...

, costal grooves refer to lateral indents along the integument of salamander

Salamander

Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...

s. The grooves run between the axilla to groin. Each groove overlies the myotomal septa to mark the position of the internal rib.