Structure
The structure of the heart can vary among the different branches of the animal kingdom. (See Circulatory system.) Cephalopods have two "gill hearts" and one "systemic heart". In vertebrates, the heart lies in the anterior part of the body cavity, dorsal to the gut. It is always surrounded by a pericardium, which is usually a distinct structure, but may be continuous with the peritoneum in jawless and cartilaginous fish. Hagfishes, uniquely among vertebrates, also possess a second heart-like structure in the tail.
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Famous quotes containing the word structure:
“If rightly made, a boat would be a sort of amphibious animal, a creature of two elements, related by one half its structure to some swift and shapely fish, and by the other to some strong-winged and graceful bird.”
—Henry David Thoreau (1817–1862)
“Each structure and institution here was so primitive that you could at once refer it to its source; but our buildings commonly suggest neither their origin nor their purpose.”
—Henry David Thoreau (1817–1862)
“With sixty staring me in the face, I have developed inflammation of the sentence structure and definite hardening of the paragraphs.”
—James Thurber (1894–1961)