After a brief notice of the seven bi-vertebral segments of the cranium in man:—

1. The hypo-cranial, or the axis and atlas vertebræ, which is adopted as a key to the cranial segments;

2. Para-cranial, or occipital;

3. Wormi-epiotic parietal, or meta-cranial;

4. Sphenoidal, or meso-cranial;

5. Ethmo-frontal—pro-cranial;

6. Nasal, or apo-cranial.

7. Rhino-nasal.

Professor Macdonald gave a short outline of the osteology of the human cranium, in order to trace the homologous osteology of the osseous fishes, or ichthyia.