SPINAL CORD 



159 



These reflex functions of the cord in mammals have been 

 very fully investigated by Sherrington in dogs and cats in 

 which the cerebrum has been separated from the rest of the 

 nervous system, and his results have been considered on p. 92. 

 On suspending such animals in the normal horizontal position, 

 with legs dependent, it is found that all four legs are in a state 

 of tonic slight extension as they are in supporting the body. 

 This he terms " decerebration rigidity." It appears to be due 

 to impulses passing down from the semicircular canal mechan- 

 ism, which reinforce the spinal reflex arcs. That this is so is 

 shown by the fact that section of the posterior roots of the 



External rotators of hi|>. 

 Hamstrings. 



Calf muscles and extrinsic muscles 

 of foot. 



Intrinsic muscles of foot. 



Muscles of bladder and urethra. 

 Extrinsic muscles of foot. 

 Intrinsic muscles of foot. 



Levator and sphincter ani. 



FIG. 79. The Groups of Cells in the Ventral Horn of grey matter at the level 

 of the 2nd, 3rd, and 4th sacral nerves. (From BRUCE.) 



spinal nerves removes the rigidity. Stimulation of definite 

 areas of skin at once causes the animal to strike a special 

 attitude (p. 95). Thus stimulation of the left fore paw 

 produces the attitude of walking, which is assumed normally 

 when that paw reaches the ground. Stimulation of the left 

 pinna produces the attitude assumed if -the animal were 

 turning away from the stimulus. 



The anatomical connection between the different levels of 

 the cord involved in such reflexes has been demonstrated by 

 Sherrington by keeping a dog in which the spinal cord is cut 

 in the neck till all the down-going tracts below the point of 

 section have completely degenerated so as to leave a clean 



