FUNCTIONS OF THE SPINAL CORD. 125 



production requires the integrity of the spinal segments from the eighth to 

 the twelfth. 



5. Epigastric reflex, consisting of a slight muscular contraction in the 

 neighborhood of the epigastrium when the skin between the fourth and sixth 

 ribs is stimulated ; it requires the integrity of the cord between the fourth 

 and seventh dorsal nerves. 



6. Scapular reflex consists of a contraction of the scapular muscles 

 when the skin between the scapula is stimulated; it depends upon the 

 integrity of the cord between the fifth cervical and third dorsal nerves. 



The superficial reflexes, though variable, are generally present in health. 

 They are increased or exaggerated when the gray matter of the cord is 

 abnormally excited, as in tetanus, strychnia poisoning, and in disease of 

 the lateral columns, leading to arrest of their normal functions. The Ten- 

 don or deep reflexes are also of great value in diagnosing the condition of 

 the spinal segments. They are induced by a sharp blow upon a tendon. 

 The following are the principal forms : 



1. Patella reflex or Knee jerk, consisting of a contraction of the extensor 

 muscles of the thigh when the ligamentum patella is struck between the 

 patella and tibia. This reflex is best observed when the legs are freely 

 hanging over the edge of a table. The patella reflex is generally present in 

 health, being absent in only 2. per cent. ; it is greatly exaggerated in lateral 

 sclerosis, in descending degeneration of the cord ; it is absent in locomotor 

 ataxia and in atrophic lesions of the anterior gray cornuse. 



2. Ankle jerk or rejlex. If the extensor muscles of the leg be placed 

 upon the stretch and the tendo-achillis be sharply struck, a quick extension 

 of the foot will take place. 



3. Ankle clonus. This consists of a series of rhythmical reflex con- 

 tractions of the gastrocnemius muscle, varying in frequency from 6 to 10 

 per second. To elicit this reflex, pressure is made upon the sole so as to 

 suddenly and energetically flex the foot at the ankle, thus putting the tendo- 

 achillis upon the stretch. The rhythmical movements thus produced con- 

 tinue so long as the tension is maintained. Ankle clonus is never present 

 in health, but is very marked in lateral sclerosis of the cord. 



The toe reflex, peroneal reflex, wrist reflex are also present in sclerosis of 

 the lateral columns and in the late rigidity of hemiplegia. 



Special Nerve Centres in Spinal Cord. Throughout the spinal cord 

 there are a number of special nerve centres, capable of being excited 

 reflexly and producing complex coordinated movements. Though for the 

 most part independent in action they are subject to the controlling influences 

 of the medulla and brain. 



