The word viscera, the plural of viscus,
refers to the soft internal organs of the body, especially those contained
within the abdominal and thoracic cavities (American Heritage Dictionary
of the English Language, Houghton Mifflin, 1996 p.1996), such as
the heart, liver, and stomach. An example would be:
In this disease, the capillaries of the skin and viscera
are narrowed.
The plural form, viscera, is used much more frequently
than the singular form, viscus, which is quite rare.
Many dictionaries do not even list the singular form, viscus;
indeed, Webster抯 New Twentieth Century Dictionary (Collins
World, 1977) defines viscus merely as "singular
of viscera. [Rare.]," while viscera
has a full definition.
Dr. Mark Multach, Chief of the Division of General Medicine at the
University of Miami, says this about viscus: "Viscus
is rarely used other than to refer to the bowel (hollow viscus).
I don't recall ever hearing any other abdominal organ referred to that
way."