The carotid body of the pheasant (Phasianus colchicus L.). An electron microscopy study.

In the pheasant, the carotid body lies laterally to the common carotid artery, is partly surrounded by parathyroid tissue and is immediately adjacent to the ultimobranchial body. In some cases these tissues intermingle. The cellular component of the carotid body consists primarily of granular endocrine cells, which are arranged in islands and lie in immediate proximity to wide capillaries and nerve fibres. A quantitative evaluation of granule size frequencies in these main cells, which we divided into three types, showed, inter alia, that the types represented three stages of cell differentiation, type III being the most mature cells. Only this last, i.e. mature, type can be used for differentiation from the granular cells of the ultimobranchial body of the same species, from which they differ. In addition, the main carotid body cells are typically surrounded by sustentacular cells. Numerous contacts with the terminal parts of axons were found on the main cells.