464 THE SPINAL CORD. 



irritation to which it is subjected. When an irritation is applied to the 

 skin on the side of the trunk, it is common to see a hind foot applied to 

 the irritated spot, as if to protect if from a repetition of the stimulus ; 

 and in some instances the adaptation of reflex movements to accom- 

 plish a definite result is very marked. This cannot be attributed to 

 any faculty of perception belonging to the spinal cord ; since we know, 

 from pathological cases in man, that when the cord is separated from 

 the brain by disease or injury, the parts below are left absolutely with- 

 out conscious sensibility or power of volition. The character of the 

 movement produced therefore depends directly upon the anatomical 

 structure of the limbs and the nervous mechanism of the spinal cord. 

 In the case of reflex action observed by Robin in a decapitated criminal, 

 the effect of gentle irritation of the skin over the front of the chest 

 was a simple movement of flexion and inward rotation of the arm and 

 forearm; and this necessarily brought the hand near the point irri- 

 tated. It is evident that the connection of the sensitive nerve fibres 

 with motor fibres, through the gray matter of the cord, may be such as 

 to call into action muscles which are adapted to accomplish a particular 

 movement, without the intervention of any perception or voluntary im- 

 pulse. This is the character of the reflex action of the spinal cord. 



As a general rule, movements of flexion are adapted to protect the 

 part from external irritation or injury, and are excited by ordinary or 

 moderate causes ; those of extension are calculated to repel the foreign 

 substance or to escape from it by moving the whole body, and are only 

 called out by an unusual or excessive stimulus. The defensive or pro- 

 tective character of these movements is often to be seen, in a state of 

 health, when the brain takes no part in their production. If the surface 

 of the skin, for example, be unexpectedly brought in contact with a 

 heated body, the injured part is often withdrawn by a rapid and con- 

 vulsive movement, before we feel the pain, or even fairly understand the 

 cause of the involuntary act. When the body by any accident suddenly 

 loses its balance, the limbs are thrown into a flexed position, calculated 

 to protect the exposed parts and to break the fall, by a similar invol- 

 untary and instantaneous movement. Notwithstanding, therefore, the 

 evident utility of these actions, they have no intentional character, and 

 there is not even any distinct consciousness of their object. 



The spinal cord has also an important action in regard to the attitude 

 and to locomotion. The preservation of the attitude alone requires the 

 harmonious action of many different muscles, all of which contribute 

 in various degrees to the position of the whole body. This is especially 

 the case in man, where, in the standing posture, the bod}*- is balanced 

 upon its narrow supports, in such a way as to preserve its equilibrium 

 without attention or fatigue. In the movements of locomotion also, the 

 different flexors and extensors of the anterior and posterior limbs are 

 associated in a manner peculiar to each species of animal ; and in man 

 the balancing of the body requires, in progression, a still more exten- 

 sive combination of muscular action than when at rest. 



