humeral cross vein

Definition

A short cross vein in the anterior (costal) region of an insect wing, connecting the subcostal vein (Sc) to the radius (R) near the humeral angle (the basal corner of the wing where it articulates with the thorax). It represents a reduced remnant of the primitive precostal area and is most conspicuous in basal pterygote lineages such as Odonata and Ephemeroptera, where it may appear as a distinct brace; in many derived insects it is lost or fused into the basal fold.

Etymology

From Latin humerus (shoulder), referring to the shoulder-like basal angle of the wing; cross vein denotes a transverse vein connecting longitudinal veins rather than running the length of the wing.

Example

In dragonflies (Anisoptera), the humeral cross vein (often labeled h) forms a small crossbar between the subcosta and radius just distal to the nodus, creating a characteristic notch in the leading edge of the forewing that aids in species identification.

Synonyms

• humeral vein
• h cross vein
• precostal cross vein

Related Terms

• cross vein
• subcosta
• Radius
• humeral angle
• nodus
• pterostigma
• wing venation
• costal margin

Usage Notes

Specialists abbreviate this structure as 'h' in wing-venation formulas. It should not be confused with the humeral vein of Diptera, which is a different longitudinal vein in the humeral callus. Presence versus absence of a free humeral cross vein is a character used in phylogenetic analyses of Paleoptera and some Polyneoptera. In relaxed or spread specimens, this delicate vein is easily torn or overlooked; it is best examined in fresh material or high-quality photographs with the wing held flat.