Fig. 1-4. (A) Light microscopy of a parafollicular cluster (arrow) in relationship to thyroid follicle (TF) (x900). (B) Parafollicular cell in characteristic position between follicular cells and follicular basement membrane, not abutting on colloid (TF) (x4,200). Tissue was obtained from normal thyroid tissue of a 26-year-old woman operated on because of a solitary thyroid adenomatous nodule. Specimens were fixed in glutaraldehyde and embedded in Araldite-502. (From Teitelbaum et al. Nature, 230,1971, with permission).