Memoirs: Some Observations on the Hypophysis of Petromyzon and of Amia
| Autor: | G. R. De Beer |
|---|---|
| Rok vydání: | 1923 |
| Předmět: | |
| Zdroj: | Journal of Cell Science. :257-292 |
| ISSN: | 1477-9137 0021-9533 |
| DOI: | 10.1242/jcs.s2-67.266.257 |
| Popis: | 1. The hypophysis of Petromyzon arises as a solid ingrowth. 2. The depression in which the hypophysis and olfactory organs come to lie is formed by the great expansion of the upper lip in conjunction with the sides of the anterior surface of the head. 3. The beginning of the histological differentiation of the glandular elements takes place from a solid strand before the appearance of any cavity. 4. The hypophysial cavity arises late as a split in the thickness of the hypophysis, and afterwards extends in both directions communicating forwards with the external depression. 5. The homologue of the pars tuberalis is probably to be found in the ‘Uebergangsteil’ of Stendell, a chromophobe portion situated between the pars anterior and pars intermedia. 6. The hypophysis of Amia is derived from the ectoderm, thus agreeing with all other known forms. 7. It arises outside the stomodaeum on the anterior surface of the head. 8. It is a solid ingrowth which loses all connexion with its point of origin, and within which the hypophysial cavity makes its appearance at a later stage. 9. Outside and in front of the stomodaeum is probably the primitive position of origin of the hypophysis, without connexion with either mouth or nose. 10. In Selachians and Amniotes where the fore-brain is early very large and the cranial flexure pronounced, the hypophysis arises further posteriorly and so is included in the hollow of the stomodaeum. 11. Although probably primitively hollow, the rudiment of the hypophysis is often solid. Such diversity is brought about by embryonic developmental conditions, perhaps the distance separating the rudiment from the infundibulum. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|