commissure

plural commissures

1. anatomyThe joint between two bones.

   ...that round about the commissure of all our joints...

   1734, William Stukeley, Of the Gout, J. Roberts, page 14

2. anatomyA band of nerve tissue connecting the hemispheres of the brain, the two sides of the spinal cord, etc.
3. anatomyThe line where the upper and lower lips or eyelids meet.

   1 more example

   There is a third inner eyelid, highly developed and of beautiful mechanism: this is the nictitating membrane, or "winker" (nictito, I wink), a delicate, elastic, translucent, pearly-white fold of the conjunctiva. While the other lids move vertically and have a horizontal commissure, the winker sweeps horizontally or obliquely across the ball, from the side next the beak to the opposite.

   1884, Elliott Coues, “§ 4.—An Introduction to the Anatomy of Birds.”, in Key to North American Birds. […], 2nd edition, Boston, Mass.: Estes and Lauriat, →OCLC, part II (General Ornithology), page 180