| Placido da Costa, Antonio | <person> Portuguese ophthalmologist, 1848-1916. See: Placido da Costa's disk. (05 Mar 2000) |
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| Placido da Costa's disk | <instrument> An instrument marked with lines or circles by means of which the corneal reflex can be observed. Synonym: Placido da Costa's disk. Origin: kerato-+ G. Skopeo, to examine (05 Mar 2000) |
| costa | <microbiology> Rod shaped intracellular organelle lying below the undulating membrane of Trichomonas. Generates active bending associated with local loss of birefringence at the bending zone, probably as a result of conformational change in the longitudinal lamellae. Major protein approximately 90 kD. (10 Nov 1998) |
| costa cervicalis | A rib which arises from the seventh cervical vertebrae (above the normal first rib). Occurs in only about 0.5% of people. May cause nerve and artery problems. (12 Dec 1998) |