Sectorial cross vein

Definition

A short transverse vein in the insect wing that connects the anterior and posterior branches of the radius (R) near the base of the wing, typically located between the radial sector (Rs) and the media (M). It helps define the boundaries of the radial cell and is a key landmark in the Comstock–Needham system of wing venation.

Etymology

From Latin sectorius (of or belonging to a sector) + cross vein, referring to its position linking sectors of the radius.

Example

In many Diptera, the presence or absence of the sectorial cross vein (r-m) is diagnostic at the family level; for instance, Syrphidae typically retain it while some other brachyceran families have it reduced or lost.

Synonyms

• r-m cross vein
• radio-medial cross vein

Related Terms

• radial sector
• cross vein
• medial cross vein
• Comstock–Needham system
• wing venation
• Radius
• media

Usage Notes

Abbreviated as r-m in standard venation notation. The sectorial cross vein is homologous across many insect orders but may be shifted, reduced, or lost in derived lineages; its position relative to the base of the radial sector is taxonomically informative. Not to be confused with the medial cross vein (m-m) or the radio-cubital cross vein (r-cu).