SPINAL CORD. !69 



3. Law of Intensity. Reflex movements are usually more intense on the side 

 of the irritation; at times the movements of the opposite side equal them 

 in intensity, but they are usually less pronounced. 



4. Law of Radiation. If the excitation still continues to increase, it is prop- 

 agated upward, and motor reaction takes place through centrifugal 

 nerves coming from segments of the cord higher up. 



5. Law of Generalization. When the irritation becomes very intense, it is 

 propagated in the medulla oblongata; motor reaction then becomes general, 

 and it is propagated up and down the cord, so that all the muscles of the 

 body are thrown into action, the medulla oblongata acting as a focus 

 whence radiate all reflex movements. 



Special Reflex Movements. 



Among the reflexes connected with the more superficial portions of the body 

 there are some which are so frequently either exaggerated or diminished in 

 pathologic lesions of the spinal cord that their study affords valuable indica- 

 tions as to the seat and character of the lesions. They may be divided into 



1. Skin or superficial, and 



2. Tendon or deep reflexes. 



The skin reflexes, characterized by contraction of underlying muscles, 

 are induced by irritation of the skin e. g., pricking, pinching, scratching, 

 etc. The following are the principal skin reflexes: 



1. Plantar reflex, consisting of contraction of the muscles of the foot, induced 

 by stimulation of the sole of the foot; it involves the integrity of the reflex 

 arc through the lower end of the cord. 



2. Gluteal reflex, consisting of contraction of the glutei muscles when the 

 skin over the buttock is stimulated; it takes place through the segments 

 giving origin to the fourth and fifth lumbar nerves. 



3. Cremasteric reflex, consisting of a contraction of the cremaster muscle 

 and a retraction of the testicle toward the abdominal ring when the skin 

 on the inner side of the thigh is stimulated; it depends upon the integrity 

 of the segments giving origin to the first and second lumbar nerves. 



4. Abdominal reflex, consisting of a contraction of the abdominal muscles 

 when the skin upon the side of the abdomen is gently scratched; its pro- 

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

 twelfth thoiacic nerves. 



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

 borhood 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 thoracic nerves. 



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



