Olfactory nerve fibres passes through?

Receptors and the first neuron: (a) The olfactory cells (16-20 million in man) are bipolar neurons. They lie in the olfactory pa of the nasal mucosa, and serve both as receptors as well as the first neurons in the olfactory pathway, (b) The olfactory nerves, about 20 in number, represent central processes of the olfactory cells. Second neuron: The mitral and tufted cells in the olfactory bulb give off fibres that form the olfactory tract and reach the primary olfactory areas. Third neuron: These are located in the primary olfactory coex which includes the anterior perforated substance, and several small masses of grey matter around it. Fouh neuron: Fibres arising in the primary olfactory coex go to the secondary olfactory coex (or entorhinal area) located in the anterior pa of the parahippocampal gyrus. Smell is perceived in both the primary and secondary olfactory areas. Ref: BD Chaurasia's HUMAN ANATOMY, Volume 3, 4th edition.