American Heritage® Dictionary of the English Language, Fourth
Edition - n. The membranous sac filled with serous fluid that
encloses the heart and the roots of the aorta and other large
blood vessels. Century Dictionary and Cyclopedia - n. In anatomy
and zoology: A somewhat conically shaped membranous sac,
inclosing the heart and the origin of the great vessels. It is
composed of two layers, an outer fibrous one, dense and
unyielding in structure, and an inner serous one, reflected on
the surface of the viscus. See cut under - n. A blood-sinus or
special cavity beneath the carapace of a crustacean, in which
the heart is suspended by ligaments and arteries, but not
otherwise connected. - n. In mollusks, the spacious dorsal cœlom
or body-cavity which is traversed by the contractile vessel
which acts like a heart. It is situated dorsad of the alimentary
canal, seldom or never contains blood-lymph, and doest not
communicate with other body-cavities, but opens upon the
exterior through the nephridia. See cuts unde