In publishing a third edition of these Memoirs, I have to express the grateful sense I entertain of the indulgence with which they continue to be received. Since the appearance of the second edition, Miss Abernethy has kindly placed at my disposal the few papers which Mr. Abernethy had preserved; and I trust that the additions they have enabled me to make, may not prove unacceptable. Besides circumstances of minor interest, interspersed through the volume, there are some of great importance. The facts relating to the marriage of Mr. Abernethy not only disprove a number of idle reports, but offer another contribution to the general kindness and sincerity of his character. In selecting a few extracts from his thoughts on Religion and Morals, I have been desirous of placing on record some of Mr. Abernethy's sentiments on these all-important questions, without forgetting that I am writing the Memoirs, not of a Divine, but of a _Philosophical Physiologist_ and _Surgeon_. In like manner, in the accompanying observations which I have submitted on the relations of Science and Religion, I have restricted myself to little more than a Layman's repudiation of a vulgar error. Some little anxiety to impress this may be excused, lest it should be supposed that an argument has been stated in a few pages, which, even in an abridged form, would require a volume; besides being inconsistent with the more measured objects of a Biographical Memoir. I have carefully avoided quoting any papers which, either by opinion or otherwise, reflected on the conduct of any party; and I have taken some pains to render this unnecessary. No man could be more sensitive than Abernethy with regard to any imputation on his honour; but that once satisfied, I am persuaded that nothing would have been more unwelcome to him than that his Memoirs should have contained, unnecessarily, one word that should offend any one; nor anything more acceptable than its avoidance under circumstances of provocation. I have had to contend with difficulties which I need not particularize; it is far more agreeable to express the gratitude I feel for that sympathy and assistance which have placed papers and documents at my disposal, with a generous confidence which, though scarcely easy sufficiently to appreciate, I trust it is impossible knowingly to abuse.