A crevasse may be as deep as 45 metres (148 ft) and as wide as 20 metres (66 ft). A crevasse may be covered, but not necessarily filled, by a snow bridge made of the previous years accumulation and snow drifts. The result is that crevasses are rendered invisible, and extremely dangerous to anyone attempting to traverse a glacier. Types of crevasses
Longitudinal crevasses form parallel to the ice flow where the glacier width is expanding. Splaying crevasses appear along the edges of a glacier. Transverse crevasses form in a zone of longitudinal extension where the principal stresses are parallel to the direction of glacier flow. Fissure vent
A fissure vent, also known as a volcanic fissure or eruption fissure, is a long volcanic vent through which lava erupts. Fissure vents are connected to deep magma reservoirs and are typically found in and along rifts and rift zones. They are commonly associated with shield volcanoes. Over time fissure vents form spatter cones and can feed lava channels and lava tubes. Karst terrain
Karst terrain or simply karst are vast regions of barren land with rocky ground and generally consisting of nearby caves, fissured ground, and sinkholes. Although these regions normally have moderate to heavy rainfall, they are noticeably devoid of vegetation and characteristically have no lakes, rivers, or streams on their surface. They form when large to massive veins of soluble aggregate like limestone, gypsum, or dolomite are excavated by underground torrents of flowing water.
Research
Equivocal preliminary results from small studies exist for:

Other dyskinesias
Huntingtons chorea
Spasmodic torticollis
Dystonia

See also
Biperiden (bicyclic ring)
Cycrimine (cyclopentanyl instead of cyclohexanyl)
Gamfexine
Procyclidine

References

 This article incorporates public domain material from Toxnet:Trihexyphenidyl. United States Department of Health and Human Services. Retrieved 8 May 2017.