In 1783, Alexander Monro published in Edinburgh 'Observations on the Structure and Functions of the Nervous System,' dedicated to the Right Hon. Henry Dundas, and it is in consequence of the description in this book of the communication between the lateral ventricles of the brain that his name is known to every student of medicine at the present day. The opening now always spoken of as the 'foramen of Monro' is very small in the healthy brain, but when abnormal accumulation of CSF on the brain is present (hydrocephalus) may be as large as a sixpence. It was this morbid condition that drew Monro's attention to the foramen, and he first described it in a paper read before the Philosophical Society of Edinburgh in 1764, but gives a fuller account in this work on the nervous system.