title: Parathyroid morphology of the brush-tail possum, Trichosurus vulpecula.
abstract: BACKGROUND
  Reviews of the comparative anatomy of the parathyroid glands contain very little or no information on this endocrine gland in marsupials. This paper is the initial report of a broader investigation of the parathyroid glands in marsupials and monotremes.
  
  
  METHODS
  Nineteen possums (Trichosurus vulpecula) were used in the study of the anatomy, histology, and ultrastructure of the parathyroid glands. Tissue sections were examined using routine light and electron microscopic techniques.
  
  
  RESULTS
  Parathyroid III is larger than parathyroid IV. The former occurs in the vicinity of the carotid bifurcation; the latter is found in the mediastinum, and in 67% of samples it was observed to be associated with thymic tissue. In parathyroid III specimens, 12.5% had follicles, 25% had cysts, and 16% contained thymic tissue. Ultrastructurally, the majority of specimens consisted of principal cells; no oxyphil cells were seen. Light and dark cells were only seen in glands that had been fixed by perfusion. Junctions between thymic and parathyroid tissues showed intervening epithelial reticular cells, but a basal lamina was not always apparent. In three specimens, cells that resembled water-clear cells were present. It is proposed that these unusual cells may reflect a state of impaired health in these possums.
  
  
  CONCLUSIONS
  Except for the presence of vacuolated cells labelled water-clear cells, the histology of the parathyroid gland in the possum shows many similarities to that in many eutherians.
authors.affiliation: Department of Anatomy and Histology, University of Adelaide, South Australia.
authors.forename: J I
authors.initials: JI
authors.lastname: Haynes
mesh_terms: D000818:Animals; D008854:Microscopy, Electron; D009893:Opossums / Q000033:anatomy & histology*; D010280:Parathyroid Glands / Q000033:anatomy & histology* / Q000166:cytology / Q000648:ultrastructure