The Evolution of the Pituitary

Abstract

The interest and importance of the pituitary for the physiologist needs no emphasising. From the point of view of comparative anatomy and evolution it is no less interesting. The ductless glands as a group seem to be characterised by peculiarities in their histories; some of these are of course well known, such as that of the thyroid originating from the endostyle of low chordates or of the pineal derived from the parietal eye. Attempts to trace the history of the pituitary have been many, but few can be regarded as satisfactory. In this study I shall attack the subject by beginning with a description of the structure of the pituitary in the mammal as a type. Its development will be outlined; and lastly, an attempt will be made to sketch out the phylogeny of the pituitary as far as is possible from the data at our disposal.