{93} (_ε_) A lesion so placed laterally in or on the pons as to affect the origin of one trigeminus (N. v.) will cause, besides motor symptoms in the face and body (types _γ_ or _δ_), special direct symptoms—viz. anæsthesia in the distribution of the fifth nerve and paralysis of the masticatory muscles opposite to the body symptoms. This is the trigeminus and body type. Lesions may be so placed ventrad or laterad upon or in the oblongata as to give rise to other types of crossed paralysis: these are easily assumed in a theoretical manner, but in practice such cases are extremely rare, present a complicated semeiology, and are usually not correctly diagnosticated during the patient's life. V. Cranio-cerebral Topography. The study of cerebral localizations from a diagnostic and practical point of view would be incomplete without a brief reference to the relations existing between the various gyri of the cerebrum and the external surface of the head, in order to render more accurate the estimation of the actual location of cerebral injuries and diseases. The surgical anatomy of the head with reference to its contents has been developed with remarkable completeness during the past fifteen years, chiefly by the researches of Broca, Bischoff, Heftler, Turner, and Féré. Acting upon these data, a number of surgeons have successfully trephined the skull for the result of injuries, for abscess, and even for tumors. The location of many convolutions and fissures of the cerebrum can be accurately mapped out upon the surface of the skull, or even upon the head of the living subject, from the projections of certain lines and measurements from points thus obtained, as well as from some natural landmarks. For the projection of these lines the head is placed in a particular position, as can easily be done when we operate upon a bare skull, but which can also be approximated when we deal with a living subject either sitting or lying in bed. The skull or the shaven head should be so placed and held that a line passing from the alveolar process of the superior maxilla and through the lowest part (condyles) of the occipital bone shall be truly horizontal. The greatest care should be used to determine this line—the alveolo-condyloid plane of Broca—for upon it all other projections and measurements are based. This position of the head and the alveolo-condyloid plane (line 1-1) are represented in Fig. 12. [Illustration: FIG.12. Topographical Lines applied to the External Contour of the Head.]