Haematobia irritans

Haemal arch (also known as the ventral arch or chevron bone) is a structure found in the anatomy of many vertebrates, including fish, amphibians, reptiles, birds, and some mammals. It is a bony or cartilaginous arch located on the ventral side of the tail vertebrae, and it serves to protect the blood vessels and nerves that run along the tail.

Structure and Function[edit | edit source]

The haemal arch is typically Y-shaped, with the arms of the Y extending upwards and the stem pointing downwards. It is located beneath the centrum (the main body of the vertebra) and is often attached to the centrum by a thin piece of bone or cartilage known as the haemal spine.

The primary function of the haemal arch is to protect the major blood vessels and nerves that run along the tail. In some species, the haemal arch also serves as an attachment point for muscles, contributing to the movement and flexibility of the tail.

Variations among Species[edit | edit source]

The structure and presence of the haemal arch can vary greatly among different species. In fish, the haemal arch is often large and robust, providing significant protection for the caudal artery and vein. In contrast, in birds and mammals, the haemal arch is often reduced or absent, as these animals have less need for tail flexibility and protection.

In some reptiles and amphibians, the haemal arch can be quite pronounced, forming a significant part of the tail's structure. In these species, the haemal arch often has additional functions, such as serving as an attachment point for muscles that control tail movement.