48 THE NERVOUS SYSTEM 



transverse myelitis^ when the disease affects the grey matter in the 

 lumbar region. The paralysed limbs are completely anaesthetic 

 and there is loss of joint and muscle sense. In most cases, 

 since the micturition centre in the hypogastric plexus (p. 373) 

 is cut off from its central connexions, there is at first retention 

 of urine, but the lower centre soon adapts itself to the altered 

 conditions and thereafter the act of micturition becomes 

 automatic. 



A complete transverse lesion in the lower cervical region 

 produces similar, but more widely spread, sensory and motor 

 paralyses. In addition, the symptoms are complicated by 

 complete interruption of the connexions between the sym- 

 pathetic system and the spinal medulla (p. 186). 



It may sometimes be difficult to determine whether a case 

 of spastic paraplegia is functional or organic in origin. If 

 the patient is placed in the dorsal decubitus and one limb is 

 passively lifted, the position assumed by the opposite limb 

 is a valuable guide. When the condition is organic, the 

 muscular rigidity causes the pelvis to become tilted, and this 

 movement of the pelvis causes the limb to be elevated slightly 

 from the bed. 



When the spinal medulla is gradually compressed, e.g. in 

 inflammation of the meninges or vertebral caries, motor par- 

 alysis is the first sign of nervous complications. As the 

 disease progresses, subjective sensory phenomena occur and 

 they are accompanied by hyperaesthesia. In the later stages, 

 there is complete motor and sensory paralysis. 



THE CEREBRAL NERVES 



The First or Olfactory Nerve is represented by a number 

 of small branches which arise from the inferior aspect of the 

 olfactory bulb. They at once pass downwards through fora- 

 mina in the lamina cribrosa of the ethmoid (Fig. 27) and 

 gain the interior of the nose, where they are distributed to 

 the mucous membrane of the septum and of the lateral wall. 



