Sentence:  The branches of these compound veins are known as <WSD>nervules</WSD>. The median vein always has three <WSD>nervules</WSD>. The <WSD>nervules</WSD> of the subcostal veins branch up and outward, with from four to five subcostal <WSD>nervules</WSD>, toward the costal margin and the apex of the forewing. 
Meaning of the word marked with <WSD> tags:  A minor vein in a wing of an insect.