mesosternum

The mesosternum is a term used in anatomy to denote the middle ventral plate (sternite) of the thorax in many arthropods, especially insects. It corresponds to the sternite of the mesothorax, lying between the prosternum (anterior) and the metasternum (posterior).

In structure and function, the mesosternum forms a ventral shield that helps define the ventral boundary of the mesothorax. It provides attachment surfaces for muscles that move the thorax and, in winged insects, can influence the base and movements of the forewings. The exact morphology of the mesosternum varies across taxa: it may be a discrete plate, or it may be fused with adjacent sternites such as the metasternum, and in some groups it is reduced or strongly ornamented with projections or sutures.

Taxonomic variation is common. In many beetles, flies, wasps, and other insects, the mesosternum shows species- or group-specific shapes and degrees of fusion with neighboring plates. Its presence and development can affect thoracic articulation, leg bracing, and wing coupling, contributing to the diversity of thoracic architecture seen across insects.

In contrast, the term mesosternum is not a standard feature of vertebrate anatomy. In humans and other vertebrates, the sternum is typically described in terms of regions such as the manubrium, body (corpus sterni), and xiphoid process rather than as anterior, middle, or posterior sternites.

See also: prosternum, metasternum, sternum, thorax.