274 Frederick Tilney, 



tuberalis [12] while its continuity with the rest of the hypophysis 

 depends on its close relation to the pars infundibularis [IS]] with the 

 latter structure it is in direct contact, the cells of one area passing 

 over into the cells of the other without any very distinct boundary 

 line. Only a small residual lumen [15] is interposed between the 

 pars distalis [14] and the pars infundibularis [13]. 



1. Histological characters of the pars tuberalis (plate XVIII, fig-. 41). 



a) Cellular arrangement. The cells are arranged in clusters of 

 deeply staining basophiles, surrounded by irregular masses of faintly 

 staining cells of the same variety. There is some tendency toward 

 the formation of acini. 



b) Cells. The cells as above indicated are of the faintly and 

 deeply staining basophilic types. 



c) Vascularity. Vascular element in this region are relatively few, 



2. Histological characters of the pars infundibularis (plate XVIII, 

 %. 43). 



a) Cellular arrangement. In this portion the cells appear in a 

 deep stratum of irregularly massed basophiles with an occasional 

 cell-cord among them. 



b) Cells. All of the cells are of the deeply staining variety. 



c) Vascularity. Vascular elements are few in number. 



3. Histological characters of the pars distalis (plate XVIII, fig. 42). 



a) Cellular arrangement. The cells are arranged as acini, cell 

 cords and masses. 



b) Cells. All varieties of cells are found. The cell cords and 

 acini are made up of faintly staining and deeply staining basophiles. 

 The cell masses consist of deeply staining and faintly staining acido- 

 phil es. 



c) Vascularity. Vascular elements are numerous. There is a 

 rich plexus of vascular channels. 



Ontogenesis of the Pars Tuberalis 

 in the Domestic Cat. 

 The development of the pars tuberalis differs chronologically and 

 topographically from that of the pars distalis and pars infundibularis. 



