By far the most common source of intra-cranial infection is chronic suppuration of the middle ear and mastoid antrum, the organisms passing from these cavities to the interior of the skull directly through a perforation of the tegmen tympani or of the wall of the sigmoid groove, or being carried in the blood stream by the emissary veins.
"Manual of Surgery Volume Second: Extremities--Head--Neck. Sixth Edition."
Alexander Miles Alexis Thomson
The trail led almost due north, again and again crossing the Little Missouri which wound in wide sigmoid curves, now between forbidding walls of crumbling limestone and baked clay, now through green acres of pasture-land, or silvery miles of level sagebrush.
"Roosevelt in the Bad Lands"
Hermann Hagedorn
O O. The sigmoid flexure of the colon.
"Surgical Anatomy"
Joseph Maclise