458 THE SPINAL CORD. 



The seat of the lesion in the spinal cord is determined by the line at 

 which paralysis of sensation and motion begins in the external parts. 

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

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

 ing parts of the trunk retain their feeling and power of motion. 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 at the same time paralysis and insensibility 

 of both upper and lower extremities, together with that of the chest and 

 intercostal muscles. A paralysis of this kind, affecting the arms and 

 intercostal muscles, is more dangerous than that of the legs alone ; 

 because a slight extension of the lesion above the middle cervical region 

 will paralyze the fibres of 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 ; because the injury or disease, when sufficient to 

 destroy one of these nervous functions, almost necessarily reaches those 

 portions of the cord which preside over the other. But in slight or 

 incomplete cases, either sensibility or movement may be more or less 

 affected, according as the lesion is more or less advanced in different 

 parts of the thickness of the cord. 



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

 voluntary motion in the right or left arm and leg, the limbs on the 

 other side of the body remaining uninjured. Sensibility and the power 

 of movement are also lost in the integument and muscles of the chest 

 and abdomen on the corresponding side. It is, therefore, a complete 

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

 exactly limited by the median line, both in front and rear. In these 

 cases the paralysis is due to some lesion within the cavity of the cra- 

 nium, on the opposite side, and above the decussation of the anterior 

 pyramids ; namely, in the upper part of the medulla oblongata, the crura 

 cerebri, the cerebral ganglia, or the hemispheres. It appears to be most 

 frequently seated in the cerebral ganglia or the hemispheres. 



In hemiplegia from this cause, the loss of sensibility and of the power 

 of motion, though occupying the same half of the body, are not necessa- 

 rily equal in degree. According to Hammond, 1 when the cause of tin 

 difficulty is a cerebral hemorrhage, they are rarely present to the 

 extent. If the lesion be situated lower down, in the crus cerebri or th< 

 tuber annulare, they would be more likely to resemble each other in degi 



When hemiplegia is due, 011 the other hand, to a lesion of the spinj 

 cord on one side, the paralysis of motion is on the same side of 

 body, and that of sensibility on the opposite side. A number of thei- 

 cases have been collected by Brown-Sequard, in most of which it 

 ascertained that the injury was seated in the lateral half of the cord 

 corresponding to the paralysis of motion. 



1 Diseases of the Nervous System. New York, 1871, p. 77. 



