400 THE NERVOUS SYSTEM. 



especially demonstrated by the effects of a longitudinal section in the 

 median line. Such a section in the lumbar region of the cord, sepa- 

 rating at that point its two lateral halves from each other, is followed 

 by complete loss of sensibility in both hind legs. This result alone 

 would not be decisive, since the suspension of sensibility might.be 

 due to the shock of the operation ; but it is of much value in connec- 

 tion with the fact that, although sensibility is lost, the power of volun- 

 tary motion is retained in both posterior limbs. 



Finally, instances in man, where a lesion of the spinal cord is accom- 

 panied by loss of voluntary motion on the same side and loss of sensi- 

 bility on the opposite side, confirm the results derived from experiment 

 on animals. The decussation of both motor and sensitive tracts is 

 completed in the upper part of the medulla oblongata ; but below this 

 point the cord acts as a conductor for motor impulses going to the 

 muscles on the same side, and for sensitive impressions coming from 

 the integument of the opposite side. 



Various forms of Paralysis, from lesions of the Cerebro-spinal 

 Axis. In consequence of disease or injury in the cerebro-spinal axis, 

 a variety of symptoms may be produced affecting sensation and motion. 

 The principal forms of paralysis from this cause are, first, " paraplegia," 

 or paralysis of the lower portion of the body and lower limbs ; and 

 secondly, " hemiplegia," or paralysis of one lateral half of the body, 

 and of one or both limbs on the corresponding side. 



I. In Paraplegia, the injury affects the whole substance of the spinal 

 cord at a particular level, and the result is loss of sensation and volun- 

 tary motion on both sides, for all parts below the level of the injury. 

 If the lesion occupy the lumbar portion of the cord, the legs and the 

 pelvic regions are paralyzed and insensible, while the arms and the 

 rest of the trunk are unaffected. If it be in the dorsal region, a 

 corresponding part of the abdomen and thorax is also deprived of 

 sense and movement ; and if situated in the middle cervical region, it 

 produces paralysis and insensibility of both upper and lower limbs, as 

 well as of the chest and intercostal muscles. A paralysis of this kind, 

 involving the arms and the intercostal muscles, is more dangerous than 

 that of the legs alone ; because a slight extension of the lesion will 

 reach the origin of the phrenic nerves, and produce death by stoppage 

 of respiration. 



In complete paraplegia, sensation and motion are both abolished in 

 the affected parts ; and injury or disease in the spinal cord, when suffi- 

 cient to destroy one of these functions, almost necessarily reaches the 

 parts which preside over the other. But in slight or incomplete cases, 

 either sensibility or movement may be more or less affected, accord- 

 ing to the intensity of the lesion in different parts of the cord. 



II. In Hemiplegia of the simplest form, there is loss of sensation and 

 voluntary motion in one upper and lower limb, and in the integument 

 and muscles of the trunk on the corresponding side. It is, therefore, a 

 complete paralysis of one lateral half of the body ; the affection being 



