This image shows some of the major structures visible on the ventral surface of
the frog brain. Note the previously mentioned olfactory lobes (2) and associated
olfactory nerves (1). On the ventral surface of the diencephalon, the two optic
nerves (4) cross to form the optic chiasma and from there extend to the optic
tracts (5) that carry impulses to the optic lobes on the dorsal surface of the
Note: The olfactory and optic nerves are but two of the 10 pairs of
cranial nerves possessed by all amphibians.
Posterior to the optic chiasma is a ventral outgrowth of the diencephalon called
the pituitary gland, or hypophysis (6). This endocrine gland (which actually
consists of two major subdivisions with different embryonic origins) regulates
many body functions including in amphibians, changes in skin color. Anterior to
the optic chiasma are the large cerebral hemispheres (3) of the
telencephalon. Once again, the medulla oblongata (7) of the myelencephalon can
be seen, along with the cranial nerves (shown in yellow on the model) that arise
from this most posterior portion of the brain.