Quantitative studies on the pars tuberalis of the hypophysis cerebri

Abstract

The pars tuberalis has been shown to be a distinct portion of the epithelial hypophysis both embryologically and histologically. 1 , 2 Whether it serves a distinct function, if any, has not been determined. 3

The method employed has been that utilized by Hammar, Rasmussen 4 and others. The three parts of the epithelial hypophysis were carefully outlined on paper of uniform thickness using serial sections and the projection microscope. The several parts were then cut out with scissors, and weighed. The volume of each part was determined in per cent of the total volume of the entire epithelial hypophysis. Then the value of the pars tuberalis in per cent of the pars intermedia was calculated.

In seventeen amphibia examined, there is great variation in the relative size of the pars tuberalis and the pars intermedia. In the tailed amphibia the pars tuberalis is relatively much larger than it is in the Anura. In Plethodon gutinosus and P. cinereus it is from one and a half to nearly five times as large as the pars intermedia.

In Ram pipiens, on the other hand, the pars tuberalis is much the smaller. In four frogs examined, the volume of the pars tuberalis was only 4 1/4 per cent of the volume of the pars intermedia.

The cat was selected as the mammalian type for this study. In this species the pars tuberalis may be distinguished with ease. The relative values for the three lobes is shown in the appended table.

Two important deductions may be drawn from our data: (1) In a number of vertebrate forms the volume of the pars tuberalis is equal or nearly equal to that of the pars intermedia; (2) As far as volume is concerned the pars tuberah may be capable of producing an important secretion in forms as high as the mammals.