Notochord (Gr. Noton - Spine, Chord - String)

The notochord (from the Greek words “noton” - back and “chord” - string) is a rod-shaped formation that runs along the longitudinal axis of the body and serves as a temporary skeleton in the embryos of all chordates. In some species it persists into adulthood, while in most higher chordates it is replaced by a vertebral column.

The notochord is one of the key characteristics of chordates and is considered one of the main reasons why these animals are grouped together. It was first described in 1827 by German zoologist Karl von Baer, ​​who noticed the similarity between the notochord and musical strings.

In embryos, the notochord appears earlier than other skeletal structures and serves as the basis for the development of the spine. The adult spine is a replacement for the notochord and consists of a series of vertebrae united by joints and separated by disc-shaped intervertebral discs.

The notochord is important in the development of embryonic tissues and organs such as the nervous system and mesodermal tissues, which differentiate into muscle, bone and connective tissue. It also serves as a fulcrum for the muscles and helps maintain the shape of the embryo's body.

In some species of chordates, such as amphioxus and lancelet, the notochord persists into adulthood and plays an important role in maintaining body shape and movement. In other species, the notochord is replaced by a spine, which performs the same functions.

Thus, the notochord is an important structure for understanding the evolution and development of chordates. Its presence in the embryos of all chordates is one of the key characteristics that unites them into one group, and it plays an important role in the development of embryonic tissues and organs.