Slide 6 Posterior Pituitary
The majority of the space is occupied by axons descended from the hypothalamus. It is thus not a true endocrine gland, but a specialization of the hypothalamus that maintains the blood brain barrier while still secreting hormones into the bloodstream by the axon endings.

Bar = 250 Microns

The dark dots in the section reflect the presence of pituicytes that are the equivalent of glia in the brain.
Expanded View