The cases that I propose to relate belong to a group either entirely overlooked or rarely met with until lately, and, doubtless, confounded with other forms of infantile paralysis. Having through the kindness of Mr. William Adams had the opportunity of seeing an example of the affection in the Royal Orthopædic Hospital, I was enabled to recognise the nature of the two first of these cases when called to see them in October last. I may observe that in a practice of upwards of thirty years, including during several years the charge of a large parochial infirmary for children, I had never recognised the disease. The association of mental imbecility with muscular paralysis, which is peculiar in these cases, has induced me to bring them under the notice of the members of this Association. In order to complete their history and to endeavour to render them the more worthy of your attention, I have embodied in my remarks the principal points that I have been able to gather from the study of M. Duchenne's pamphlet.∗