824 



THE SPINAL CORD. 



To excite movement of one fore-limb from the other is less easy than to excite 

 one hind-limb from the other, at least in many animals. In the neck region 

 irradiation across the median sagittal plane is fairly easy, and the yoking 

 connects in large part asymmetrical muscles. 



On the whole the long spinal reflexes are more variable and less 

 certain and validly predictable than the short. They vary in a series 

 of experiments, not only as to order of relative facility of direction of 

 irradiation, but especially as to the sense of the movement elicited 

 at the joint, whatever it may be, to which irradiation extends. Not 

 unfrequently a region to which the reflex action usually demonstrably 

 irradiates is altogether omitted, and omitted consistently throughout 

 the whole of a lengthy experiment, although the spinal region in 

 question has as far as known suffered no damage, nor indeed been 



Fig. 357. — Diagram of irradiation of reflex movement in spinal cat in response to 

 stimuli applied — 1, to left hind-foot ; 2, to left fore-foot ; 3, to left pinna. 

 The movements of the head are included in 1 and 2. The numbers attached 

 to the limbs, etc., indicate the order usually taken by the parts in the 

 "march " of the reaction. 



directly implicated in any of the procedure. Thus excitation of the 

 skin of the neck or pinna will sometimes spread back along the cord 

 and produce movement in the tail or in the hind-limbs, and in doing so 

 pass by the fore-limbs without evoking a twitch in either of them. The 

 motor mechanisms of the fore-limb thus skipped over may show no sign, 

 when examined by the local reflexes, of being less amenable than usual. 

 Besides the limb movements, some other reflexes involve considerable 

 co-ordination of trunk muscles, thus the " shaking " of the body on 

 stimulating the skin of the back and shoulder. This seems analogous 

 to the shaking of the head and ears on stimulating the ears, well seen in 

 the bulbo-spinal dog. Related to it appears the " scratching " movement 

 called from the hind-limb by rubbing the flank or shoulder. 



There seems in the spinal mammal a disproportionate restriction of 

 the range of spread of the reaction below the normal range. It is 

 true that in response to a stimulus, e.g. of the skin of the normal animal, no 



