Pertaining to rudiments or first principles; consisting in or dealing with first principles; elementary; initial: as, rudimentary teachings; rudimentary laws.Of the nature of a rudiment; elementary; undeveloped.Specifically, in biology: Pertaining to or of the nature of a rudiment; rudimental; beginning to be formed; elementary; embryonic.Vestigial; abortive; aborted or arrested in development; having no functional activity.Synonyms Rudimentary. Vestigial, Abortive. These three words, in their biological application, are commonly used interchangeably, and may mean exactly the same thing. But there is a clear and proper distinction in most cases, since that which is rudimentary in one organism may be fully developed in another organism, and that which is rudimentary in a given organism may or may not proceed to develop in that organism. So that which is developed in one organism but remains rudimentary in another is vestigial for the latter—that is. it affords a mere trace or hint of the former; and that which might have developed but did not develop in the same organism is abortive. Thus, all embryonic parts and organs are properly rudimentary; all functionless organs are vestigial which in another case have become functional; those which are normally functional but fail to become so in a given case are abortive. Rudimentary is the most general and comprehensive term for that which is rude, raw, crude, unformed, in an absolute sense; vestigial is a relative term, implying comparison with something else, of which that which is vestigial is a mere trace; abortive is likewise a relative term, but one implying arrest or failure of development in the thing itself, without reference to any other thing. Few if any organs can be described with equal accuracy by all three terms, though the distinctions are often ignored. Vestigial is a more technical term than either of the other two, implying a broad view of the thing described, derived from comparative anatomy and physiology, according to the theory of evolution. Abortive is specially applicable to pathological and teratological cases. A harelip or cleft palate is abortive, but neither vestigial nor rudimentary. The thymus of the adult is vestigial, but neither abortive nor rudimentary. The brain-bladders of the embryo are rudimentary, but neither vestigial nor abortive. Most of the functionless and apparently useless organs of adults of the higher animals are most properly to be designated as vestigial.
