DEVELOPMENT OF THE HYPOPHYSIS 399 
remain separated. The distal ends of the tubules are solid and 
by means of branches anastomose with the cords of the other 
tubules. The arrangement of the cells here is the same as that 
in the dorsal lobe. This portion stains more deeply, the capil- 
laries are smaller and less numerous. The endocranial portion 
in embryos is a sac with folded walls. In the adult, many 
tubules and cords have developed. In the main this resembles 
the rostral portion of the perimeningeal part. 
Tilney (11) in his studies on the comparative histology of the 
hypophysis, stated that in Acanthias there is a distal epithelial 
portion made up of parallel cell columns. The cells are deeply 
acidophilic with only a few faintly-staining acidophilic ones 
present. In the juxta-neural part the cells are larger, usually 
irregularly disposed, but forming some acini. However, they 
take the basic stains very markedly. He found this portion 
less vascular than the distal part. Tilney has homologized the 
different portions of the hypophysis in the various vertebrate 
groups. The distal epithelial portion of selachians corresponds 
to the intermediate lobe of mammals. 
In 1913 Stendell made a comparative study of the hypophysis. 
He described intermediate and main lobes in Heptanchus. In 
the mainlobe he described the peripheral cells of the tubules 
as of an acidophilic nature, while those toward the center are 
basophilic or neutral. Stendell has homologized the parts 
found in the hypophysis of selachians with those in the higher 
forms of vertebrates. His homology agrees with that of Tilney, 
i.e., the intermediate lobe of Heptanchus is homologous with the 
same portion in the higher vertebrates, being in Heptanchus 
very large and becoming smaller in the higher forms. The 
ventral sac of the main lobe is not found in higher forms. 
There have been many terms used in the descriptions of the 
different parts of the elasmobranch hypophysis. A comparison 
with figure 1, which is a drawing of a model of the hypophysis 
of a pup, and a table of the terms employed may serve to explain 
the terms used in reviewing the literature. 
