(_b_) Two homonymous extremities or the two lateral halves of the body may exhibit opposite states of sensibility—anæsthesia on one side and hyperæsthesia on the other. This rare condition is witnessed in hysteria and in some forms of injury to the spine (lesion of one lateral half of the cord at a certain level). In the latter case paralysis is usually present on the hyperæsthetic side: the symptoms constituting, with some others, Brown-Séquard's spinal hemiplegia or hemiparaplegia. (_c_) Alterations of sensibility in one caudal (horizontal) half of the body are said to have a paraplegic distribution, and are usually due to lesions of the spinal cord. The upper level of the symptom may be at any point between the neck and the toes; and the frontal (upper) level indicates, due regard being had to the origin and oblique distribution of the spinal nerves, the highest limit of disease in the nervous centres. Very often, in organic disease especially, this is also indicated by the presence of a cincture feeling (paræsthesia) at the frontal (upper) limit of the anæsthesia, etc. (_d_) Disorders of sensibility may be limited to one extremity. This very rarely depends upon cerebral disease, and in such a case the anæsthesia, etc. is evenly distributed throughout the member, being most intense at its extremity, and being without sharp, distinct limits near the trunk. When due to diseases of the spinal cord, the cerebral (upper) limit of the symptom is usually clearly defined in accordance with the distribution of sensory nerves from the other (healthy) parts of the cord: a constriction band often marks the limit. Sometimes the peripheral anæsthesia, etc. is more or less in the territory of certain nerve-trunks. When we find the distribution of the sensory symptoms to coincide exactly in the areas supplied by the large nerves of the limb, without cincture feeling, it is certain that the lesions affect one or more of these nerve-trunks or the plexus above. In not a few cases the symptoms are due to hysterical or dyscrasic conditions, and the seat of the lesions (dynamic or molecular lesion) is uncertain. In judging of the distribution of anæsthesia, etc. in a limb due regard must be paid to variations in nerve-branching and to collateral nerve-supply.