(_a_) Diffused bilateral lesions of this class situated frontad of the crura give rise to more or less distinct symptoms, and a diagnosis is sometimes possible. (1) Lesions in the vicinity of the sella turcica and optic chiasm produce symptoms in the optic apparatus very early, and these remain prominent throughout the illness. These symptoms are, irregular (at least not lateral) hemianopsia, neuro-retinitis followed by atrophy of the optic nerve, temporary or permanent paralysis of one or several ocular nerves. If these exist without symptoms of lesion of other parts of the brain (reasoning by the process of exclusion), we may strongly suspect the seat of the lesion to be in the region named. Other symptoms are paroxysmal headache and occasional vomiting, epileptiform convulsions (never Jacksonian in distribution), partial hemiplegia, or general muscular weakness. By such data we were recently led to the correct localization of a tumor. (2) If the lesion be farther frontad—_i.e._ strictly in the orbital areas of the basis cerebri—anosmia, uni- or bilateral, usually with hallucinations of smell, will be an early symptom, along with neuro-retinitis and obscure motor and sensory symptoms (headache and convulsions more especially). (_b_) Lesions situated caudad of the infundibulum. (1) Bilateral lesions give rise to symptoms which are the symmetrical duplication on either side of the face and body of those to be next described as characteristic of— (2) Unilateral focal lesions of the base of the encephalon from the crura caudad to the pyramidal decussation. In a general way, the symptoms of these lesions are designated as varieties of crossed paralysis. Clinically, a crossed paralysis is one in which one or several cranial {92} nerves show symptoms of irritation or destruction on one side of the median line, while body symptoms are present on the opposite side. Physiologically and anatomically, a crossed paralysis is one in which the lesion is so placed as to affect a cranial nerve (or more than one) at a point caudad (below) of the decussation of the fibres which connect its nucleus with the cerebral cortex, or at its nucleus of origin, or so as to injure the nerve-trunk itself; while at the same time the lesion affects the main fasciculus of the pyramidal tract frontad (above) of its decussation, in the crus, pons, or oblongata. In many cases of crossed paralysis, besides common motor and sensory symptoms, there is apt to be neuro-retinitis with its consequences. The chief forms or types of crossed paralysis are: