The vascularization of the pituitary in elasmobranchs

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Abstract
Hypophysial vascularization is described in members of the genera Squalus, Etmopterus, Scyliorhinus, Pristiurus and Raja. The anterior lobe lacks arteries and is supplied by a pituitary portal system. The collecting area of this system covers the median eminence, but also receives capiIIaries from adjacent hypothalamic nuclei. The two regions of the anterior lobe belong to different regions of the portal system. The neuro-intermediate lobe is usually supplied with arteries, but in some cases receives vessels from the median eminence (Scyliorhinus, Raja). There is a possibility of neurovascular control of the intermedia through vessels from the neural lobe (Squalus, Etmopterus). Lateral afferent veins bring blood from a wide hypothalamic area to or through the neuro-intermediate lobe (not in Squalus). The functional significance of the vascular pathways is, discussed, and an attempt at an evolutionary derivation of the portal system is given.