In the first place, he observed that the raising of the bone could only be necessary _where it produced symptoms_. He also observed that experience had recorded certain cases in which, notwithstanding that the bone had been depressed, the patients had recovered without any operation. Then again he thought it not improbable that, where the depression was slight, even though some symptoms might at first arise, yet, if we were not too precipitate, we might find that they would again subside, and thus so serious an operation be rendered unnecessary. These and similar reasonings led him to recommend a more cautious practice, and to refrain from trephining, even where the bone _was depressed_, except on conditions which referred to the general effects of pressure _on the brain_, rather than to the abstract fact of depression of the bone. He did not stop here; but having thus placed restrictions on the use of the trephine, where it had been too indiscriminately employed, he then describes the practice which is to be pursued where the pressure is produced from _effusion_ on the brain. Although, in laying down the rules to be observed in such cases, there is much of painful uncertainty as to the existence of effused blood, the site it may occupy, and other circumstances of embarrassment,—still the rules he proposes in relation to the avoidance of large vessels, the condition of the bone as indicative of the actual state of the parts beneath it, &c. are all clearly and beautifully stated, as deducible from the anatomical and vascular relations of the parts. The result of all this discrimination is, that the trephine is seldom employed, whilst the treatment of the various injuries of the head is much more successfully conducted. He next proceeds to consider the distinction between those cases in which the brain has been _shaken_ merely (concussion), and those where it has been subjected to mechanical pressure. There are two points in this part of the paper of great interest to the practical surgeon: the one in which he treats of the distinction of the two cases; the other, in which he marshals the discordant practices of different surgeons in cases of concussion, and defines the proper phase of the case in which we may make them respectively applicable. When, for example, we may by warmth maintain, or even by cautious stimulation excite, the depressed powers; or, by judicious abstinence from either, avoid provoking too violent reaction; and, lastly, how we should combat the latter, if it unfortunately supervene.