Middle meningeal hæmorrhage, uncomplicated by brain injury, is of infrequent occurrence, the associated injuries to bone and brain confusing the diagnosis. Moreover, the special pressure effects are dependent not only on the absence of serious brain lesion, but also on the non-existence of a safety-valve, such, for instance, as is afforded by a comminuted fracture of the bones entering into the formation of the temporal fossa, or of the roof of the middle and external ears. In the former case, blood will force its way into the temporal region, there forming a temporal hæmatoma--one that may pulsate--whilst, in the latter case, the blood escapes freely from the external auditory meatus. It should be noted, however, that pressure applied to the temporal hæmatoma may lead to the development of irritative or paralytic symptoms confined to the muscles of the opposite side of the body, whilst the restriction of aural bleeding, by means of plugs inserted into the ear, will lead to the early development of compression symptoms. The amount of blood extravasated varies--according to the calibre of the vessel involved--from a drachm to several ounces. The largest coagulum that has come under my observation was 4¹⁄₂ inches in the long diameter and 1 inch in thickness. Krönlein narrates a case in which the clot weighed 9 ounces. [Illustration: FIG. 50A. THE INNER ASPECT OF THE SKULL.] [Illustration: FIG. 50B. THE INNER ASPECT OF THE SKULL SEEN ON TRANSILLUMINATION.] In shape the clot is elliptical; in consistency it is either fluid or jelly-like. During the early stages of its formation it can be readily removed. Later on, it adheres to the dura mater, and, when removed, leaves that membrane rough and discoloured. Some uncertainty exists as to the relative frequency with which the trunk and the two terminal branches are exposed to injury. There can be no doubt that the majority of cases in which typical clinical symptoms are present are such as evidence injury to the anterior terminal division; this is due to the anatomical relation of the clot to the motor cortex. Injury to the main trunk is of the rarest occurrence, for the foramen spinosum lies immediately anterior to the petro-sphenoidal suture, the course pursued by typical middle fossa fractures. I have seen one case only, and have read the accounts of two others, in which the foramen spinosum was directly implicated.