Spastic paralysis of voluntary Flaccid paralysis of voluntary muscles. muscles. No marked wasting of paralysed Marked wasting of paralysed muscles. muscles. No reaction of degeneration. Reaction of degeneration. Exaggeration of reflexes. Loss of reflexes. Irritative lesions of the sensory mechanism cause numbness and tingling (paræsthesia); more extensive paralytic lesions produce anæsthesia, astereognosis, loss of muscle sense, loss of pain, or inability to distinguish temperature, according to the tracts that are affected. _Lesions of the Upper Motor Neurone_ may occur in any part of its course. _Localised lesions of the motor cortex_ of an irritative kind, for example, a patch of meningitis, a tumour, meningeal hæmorrhage, or a spicule of bone, produce spasms in those groups of muscles on the opposite side of the body that are supplied by the centres implicated--Jacksonian epilepsy. The cortical discharge may overflow into neighbouring centres and cause more widespread convulsive movements, or, if strong and long-continued, may even lead to general convulsions. Consciousness is usually lost before the whole of one side becomes implicated in the spasms; always before they spread to the opposite side. Contracture may occur in the muscles affected after the spasms cease. If an area of the cortex is destroyed by the lesion, paralysis is produced of the corresponding muscles on the opposite side of the body. At first the paralysed muscles are flaccid, but spasticity soon develops. In some cortical lesions, for reasons not yet understood, the paralysis remains of the flaccid type. The seat and extent of the paralysis depend upon the area of the cortex destroyed. In rare cases the whole motor area is destroyed--_cortical hemiplegia_; more generally the lesion affects one or more groups of muscles, and occasionally all the muscles of one limb are paralysed--_cortical monoplegia_. Lesions are often both irritative and destructive, and lead to paralysis of one or more groups of muscles associated with spasms and convulsions of the muscles governed by neighbouring areas of the cortex. Irritation or destruction of the sensory centres may also exist, giving rise to areas of paræsthesia and anæsthesia. Lesions in the _centrum ovale_, which destroy the fibres proceeding from the overlying cortex, produce a corresponding spastic paralysis on the opposite side of the body. No irritative phenomena are associated with such a sub-cortical lesion. Lesions in the region of the _internal capsule_ often produce complete spastic hemiplegia of the opposite side of the body. When the posterior part of the capsule is involved, there are, in addition, hemianæsthesia and hemianopia, and sometimes disturbances of hearing, smell, and taste.