532 THE THORAX AND VERTEBRAL COLUMN 



segment is indicated by the collapse of the upper limbs upon 

 the trunk. 



In transverse lesions of the spinal medulla occurring between 

 the fourth cervical and the second thoracic segments the limit 

 of anaesthesia on the anterior surface of the body is placed at 

 the level of the second costal cartilage (p. 530). The distribution 

 of the areas of altered sensibility in the upper limbs gives an 

 indication of the exact level at which the spinal medulla is 

 injured. When a lesion occurs below the second segment in the 

 thoracic region, the upper limit of the anaesthesia corresponds to 

 a horizontal line drawn round the trunk at the level of the 

 terminal branches of the intercostal nerve which arises from the 

 injured segment. As the thoracic nerve-roots pass downwards 

 before they leave the vertebral canal, and as the nerves sub- 

 sequently descend for some distance before they terminate 

 (p. 240), the site of the injury to the vertebral column is placed 

 at a much higher level than the upper limit of the anaesthesia. 



A complete transverse lesion of the spinal medulla in the lower 

 thoracic region is accompanied by total motor and sensory 

 paralysis of both lower limbs. Although the lesion in the 

 vertebral column is above the level of the transpyloric plane, 

 the muscles of the abdominal wall, which are supplied by the 

 seventh to twelfth thoracic nerves, are little affected, and the 

 cutaneous sensibility is altered only in the lowest part of the wall. 

 Reflex evacuations of the bladder and rectum occur, as the lesion 

 is above the level of the spinal centres for these viscera (p. 529). 



In complete transverse lesions above the level of the seventh 

 thoracic segment all the muscles of the abdominal wall are 

 paralysed and the condition of meteorism supervenes ; owing 

 to the absence of the expulsive force, gas accumulates in the 

 alimentary canal and the abdomen becomes greatly distended. 



Fracture dislocation in the lumbar region of the vertebral 

 column involves the cauda equina. All the nerve-roots of the 

 cauda are rarely affected, and the alteration of sensibility in the 

 saddle-shaped area supplied by the third sacral nerves (Fig. 116) 

 is usually asymmetrical. As the condition arises from a root 

 injury, the area of epicritic loss is smaller than the area of 

 protopathic loss (p. 97). In these cases the bladder and 

 rectum are often affected, but the paralysis is rarely complete. 



Fracture of the Articular Processes alone does not necessarily 

 give rise to symptoms of nerve pressure. 



Surgical Approach to the Spinal Medulla. It may be 



