#1. The organ of Jacobson of the
Sphenodon is well developed. It is mammalian rather
than reptilian in type and is very similar to that of
the ornithorhyncus. It gives the Sphenodon a place
in mammalian phylogeny that is nearer the main line
of descent than that of any other reptile hitherto
#2. There is an accessory bulb in the
Sphenodon. It receives from the organ of Jacobson.
It is primitive in type, showing no lamination.
Its cells are different in character from those of
the olfactory bulb. This supports the theory that
the accessory bulb is an earlier development than the
olfactory bulb and that the organ of Jacobson with
which it is related represents the olfactory organ of
fishes. The structure of the accessory bulb gives
information of phylogenetic value and indicates that
the Sphenodon abandoned its aquatic life when very
#3. The olfactory bulb is of the reptilian
type and its cells are well differentiated.
#4. The axons of the two bulbs - accessory
and olfactory - intermingle and probably are distributed to the same centres in the hemisphere.
#5. There is in the Sphenodon what corresponds with the reptilian anterior olfactory nucleus.
It is formed by the attenuated rostral tip of
different parts of the cortex of the hemisphere and
is not a detached cell mass.