The Comparative Physiology of the Pituitary Body 263 



The posterior lobe is smaller than the anterior, and overlaps it slightly 

 behind. It is hollow, and its cavity is continuous through a narrow neck 

 with the third ventricle of the brain. The lobe is occasionally much con- 

 voluted, and its cavity appears at several points in the same section. Its 

 wall is never very thick, and seems to consist chiefly of long ependyma 

 cells, true nerve-cells being absent from it. Colloid bodies are not infre- 

 quently present, and the cavity often contains much debris and occasionally 

 rounded clumps of what resemble epithelial cells. In the extension of its 

 cavity by recesses and the convolutions of its wall the posterior lobe sug- 

 gests a glandular structure opening into the third ventricle. Like the 

 posterior lobe of the mammalian pituitary, that of the fowl possesses an in- 

 complete covering of epithelial cells, which are constantly found in certain 

 positions. They resemble in structure and in their relationship to nervous 

 tissue the cells of the pars intermedia of the mammalian pituitary, and are 

 probably to be regarded as having the same significance. These cells form 

 layers closely investing the nervous substance of the neck of the posterior 

 lobe, and extending forwards between the anterior lamina of the neck and 

 the optic chiasma (fig. 1 of Plate). The layers are few in number, and well 

 supplied by blood-vessels ; in fact, the cells often appear to have extended 

 along the sheaths of the blood-vessels. They spread around the neck of 

 the posterior lobe and for a considerable distance backwards over the thin 

 lamella forming the lower wall of the third ventricle. The body of the 

 posterior lobe lies behind, directly upon the anterior lobe, but is readily 

 separated from it. No epithelial cells are seen on its posterior and upper 

 surface, but they are often found laterally, and extend with the blood- ve.ssels 

 into the spaces between the folds of the lobe. In the fowl, therefore, the 

 cells of the pars intermedia come into close contact with the nervous tissue 

 of the posterior lobe, but are aggregated for the most part in the neighbour- 

 hood of its neck and on the thin lamina of nervous tissue forming the floor 

 of the third ventricle. It is easy to separate the anterior lobe from the 

 posterior, but impossible to remove the nervous tissue of the posterior lobe 

 without at the same time including epithelial cells of the pars intermedia 

 and their products. 



B. Haller (2) studied tlie pituitary of Gallus doraesticus and describes 

 two portions in the anterior lobe, one of which, the superior, is closely 

 applied to the infundibulum. The other portion, or anterior lobe proper, 

 Haller believes to be tubular, and to constitute a gland whose secretion is 

 poured into the subdural space by a small mesial opening. Haller noted 

 the diverticula in the posterior lobe, and states that the arrangement met 

 within it gives the lobe a glandular appearance. 



Sterzi (11) examined the pituitary of several species of birds, and 

 describes a division of the anterior lobe into two parts, one of which is 

 made up of chromophobe cells and nearly surrounds the posterior lobe, 

 while the other, more massive, consists of chromophil cells. 



Gentes (1) also describes two segments in the anterior lobe. One of 



