Unless a practitioner be thoroughly acquainted with every step in the mechanism of a natural labour, how can he be expected to understand and detect with certainty any deviation from its usual course, still less make use of those means which may be required under the particular circumstances of the case; and yet, strange to say, there are few subjects which, generally speaking, have excited so little attention, and upon which such incorrect opinions have prevailed even up to the present time. The investigation is confessedly one of considerable difficulty, and as it was more easy to calculate how the head ought to pass in this or that position through the pelvis than to ascertain how it really did pass, ingenuity has been taxed, and theories have been invented, and positions of the child without number have been described, which have never existed in nature, and which have only added to the difficulty and perplexity of the subject. We consider that to form an accurate diagnosis in these cases, requires the highest perfection of the _tactus eruditus_, which can only be acquired by long practice and patient observation: and it is chiefly from this circumstance that we can explain why such gross errors and vague notions should have existed about a process of every day occurrence, and why, with but few exceptions, they should have been transmitted from one author to another even up to the present time. In the last century, when it was so much the fashion to resolve every physiological process into a mathematical problem, it was scarcely deemed necessary to spend much time in actual observation and examination; the proportions between the head and pelvis were ascertained, their angles were measured, and their curves determined, and from these data it was inferred, what must be the course which nature would follow; few attempted the slow but surer method of ascertaining by patient research the real facts connected with the process of parturition.