Vomero-nasal organ, the accessory and olfactory bulbs, and the anterior olfactory nucleus of the Sphenodon punctatum

Abstract

#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 investigated.

#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 primitive.

#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.