640 



THE NERVOUS SYSTEM 



are distinctly limited to particular groups of muscles; with stronger currents 

 the stimulus is communicated to other muscles of the same or neighboring 

 parts. 4. The portions of the brain intervening between these motor centers 

 are inexcitable. 



FIG. 401. Brain of Dog, A, Viewed from Above and B in Profile. F, Frontal fissure 

 sometimes termed crucial sulcus, corresponding to the fissure of Rolando in man; S, 

 fissure of Sylvius, around which the four longitudinal convolutions are concentrically 

 arranged; i, flexion of head on the neck, in the median line; 2, flexion of head on the neck, 

 with rotation toward the side of the stimulus; 3, 4, flexion and extension of anterior limb; 

 5, 6, flexion and extension of posterior limb; 7, 8, 9, contraction of orbicularis oculi and the 

 facial muscles in general. (Dalton.) 



Following strong stimulation of cortical motor centers other groups of 

 muscles than those innervated by the centers stimulated may also take part in 

 the contractions. 



According to the further researches of Schafer and Horsley, electrical 



