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Updated: July 23, 2025
It is exactly similar in structure and arrangement to the tricuspid valve, except that it is stronger and is composed of two parts instead of three. B. Right semilunar valve. The tricuspid valve and the chordæ tendineæ shown in the ventricle. The right semilunar valve is situated around the opening of the right ventricle into the pulmonary artery.
It is fairly well developed in the two lower divisions of the mammalian series, namely, in the monotremata and marsupials, and in some few of the higher mammals, as in the walrus. But in man, the quadrumana, and most other mammals, it exists, as is admitted by all anatomists, as a mere rudiment, called the semilunar fold. Muller's 'Elements of Physiology, Eng. translat. 1842, vol. ii. p. 1117.
Vogt, Karl, on the origin of species; on the origin of man; on the semilunar fold in man; on microcephalous idiots; on the imitative faculties of microcephalous idiots; on skulls from Brazilian caves; on the evolution of the races of man; on the formation of the skull in women; on the Ainos and negroes; on the increased cranial difference of the sexes in man with race development; on the obliquity of the eye in the Chinese and Japanese.
On the right side, in front of the external half of the sclerotic, was observed a semilunar fold with the concavity inward, and which projected much more when the lower lid was depressed. When the eyelid rolled inward the fold rolled with the globe, but never reached so far as the circumference of the cornea and did not interfere with vision.
In one important point veins differ structurally from arteries namely, in being provided with valves which prevent reflux of the blood. These valves are composed of semilunar folds of the tunica intima strengthened by an addition of connective tissue.
This is so useless in man that it can be explained only as a survival. There are some other survivals in man of ancient structures to which a passing allusion must suffice. In man's eye is a minute membrane, the semilunar fold, which is absolutely useless in his economy.
Oh no! but what dull ache is this in that obscurely sensitive region, somewhere below the heart, where the nervous centre called the semilunar ganglion lies unconscious of itself until a great grief or a mastering anxiety reaches it through all the non-conductors which isolate it from ordinary impressions?
The celebrated Hieronymus Fabricius of Aquapendente, a most skilful anatomist, and venerable old man, or, as the learned Riolan will have it, Jacobus Silvius, first gave representations of the valves in the veins, which consist of raised or loose portions of the inner membranes of these vessels, of extreme delicacy, and a sigmoid or semilunar shape.
But if the divine Galen will here allow, as in other places he does, "that all the arteries of the body arise from the great artery, and that this takes its origin from the heart; that all these vessels naturally contain and carry blood; that the three semilunar valves situated at the orifice of the aorta prevent the return of the blood into the heart, and that nature never connected them with this, the most noble viscus of the body, unless for some important end"; if, I say, this father of physicians concedes all these things, and I quote his own words, I do not see how he can deny that the great artery is the very vessel to carry the blood, when it has attained its highest term for term of perfection, from the heart for distribution to all parts of the body.
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