The fine structure of the infundibular process of the hedgehog

Summary The fine structure of the infundibular process of the hedgehog has been studied, using material fixed in osmium tetroxide and embedded in Vestopal W. The process resembles in general structure that of other mammals, but also shows features not previously described in other species.The nerve fibres contain a number of inclusions, namely: small vesicles, 300–500 Å in diameter; larger vesicles, up to 2000 Å in diameter, which contain a variable amount of osmiophilic material; hexagonal crystal-like bodies, approximately 1250 × 3000 Å in size, lying within a striated membranous sheath; and aggregate bodies made up of small electron dense granules, possibly derived from mitochondria.In addition complex multilamellate bodies occur in some nerve fibres, which apparently give rise to membranous vesicles. Pituicytes, of varying appearance, are often intimately related to the nerve fibres.The findings suggest that synthesis of material may occur in the distal part of the fibres of the hypothalamo-hypophysial tract.We are indebted to the Medical Research Council, who provided the electron microscope in the Department of Anatomy, University of Birmingham, which was used in this study.