(_c_) Paraplegia.—The loss of voluntary power involves one transverse half of the body, usually the caudal. When only the lower extremities are affected, the condition is designated simply a paraplegia; when all the parts below the head are paralyzed, the term cervical paraplegia is employed. Frequently, the bladder and rectum are paralyzed, and in some cases the thoracic muscles also, leaving inspiration to be performed by the diaphragm alone. Often there is coextensive anæsthesia. {44} Hemiparaplegia is a rare variety in which one lower extremity is paralyzed while the other is anæsthetic. The location of the lesion in paraplegias is in the spinal cord at various levels and in various portions of the gray and white columns. Theoretically, we may now again admit the old proposition that a paraplegia may be of cerebral origin: in such a case the loss of power should follow the laws of distal prevalence (vide (_α_)); there should be no anæsthesia or vesical paralysis, and the lesion ought to be one involving the paracentral lobules of both hemispheres (meso-vertex at fissure of Rolando). (_d_) Monoplegia, or paralysis of one extremity or of one side of the face, is not rarely observed. It may be caused by central lesions in the brain or spinal cord, or by an affection of the nerve-trunks of the part. Cerebral monoplegias are of great importance in diagnosis, and may be distinguished from others by—(1) loss of power is greatest in the distal part of the affected member; (2) the precedence or coincidence of spasm (usually clonic or epileptiform) in the limb; (3) the absence of marked anæsthesia; (4) the preservation of muscular nutrition. (_e_) Localized Paralysis.—The extreme types of this form of paralysis are paralysis of one external rectus and of one superior oblique. These muscles are each supplied by one whole nerve, and may therefore exhibit isolated paralysis. In the rest of the body, however, localized paralysis shows itself in groups of muscles as innervated by nerve-trunks or by certain so-called centres in the spinal cord. As examples of the former variety may be cited common facial paralysis (Bell's palsy) and paralysis of the extensor muscles of the hand by injury to the musculo-spinal (radial) nerve, of the foot and leg from lesions of the sciatic nerve. As examples of the second variety we have the irregular paralysis of anterior poliomyelitis (infantile spinal paralysis). In localized paralyses due to lesion of the nerve-trunks anæsthesia is usually present, whereas it is not common in the second variety. The determination of the seat of lesion in neural localized paralysis is much facilitated by bearing in mind Van der Kolk's law of the distribution of the motor and sensory fibres of a nerve-trunk. Pseudo-paralysis—_i.e._ conditions in which voluntary motion is lost without defect in innervation, as from muscular disease, injuries, inflammations, etc.—is usually localized or irregularly distributed.