THE NERVOUS SYSTEM 



495 



e.m 



function of its localities ; the subject is generally spoken of as 

 the localisation of cerebral junction. 



The Motor Area. — A region of the brain of the monkey or 

 man, known as the fissure of Rolando, is intimately connected 

 with the cells which give rise to the motor nerves passing to 

 muscles. In the dog there is no fissure of Rolando, but there is 

 a fissure, known as the frontal or crucial sulcus (Fig. 148, c.s.), 

 in which the motor cells for the muscles are localised as in the 

 fissure of Rolando, and 



similar localities must § \j ft 



exist in other animals, 

 although, with the ex- 

 ception of the sheep, 

 dog, cat, rabbit, and 

 monkey, little has been 

 done to identify them. 



If the brain in the 

 region of the crucial 

 sulcus of the dog be 

 exposed, and the part 

 stimulated electrically, 

 the muscle, or group of 

 muscles, contract which 

 are connected with those 

 cells of the cortex im- 

 mediately beneath the 

 electrode. It is remark- 

 able that a great Euro- 

 pean war was necessary 

 to demonstrate this fact, 

 but physiologists for 

 years remained in this 



matter under the influ- The areas are only marked on the left side of 

 ence of the teachings Of tne n 8 ure except the eye areas, whose position, 

 t^, , ir • !• to avoid confusion, is indicated on the right 



Flourens and Majendie, hem is P here. 

 who stated that the 



cerebral cortex was inexcitable. Gradually the knowledge 

 derived from stimulation of the cortex has accumulated, until 

 a very remarkable picture of the cortical functions can 

 be obtained. Fig. 149 shows the motor area of the chim- 

 panzee ; that for man is still more complex. The size of a 

 motor area bears a relation to the degree of complexity of limb 

 movements. The limb movements in quadrupeds are simple ; 

 for instance, in the horse they are mainly pendular ; in the dog 

 they are more complicated ; and still more so in the cat, in which 

 the delicate movements of face- washing are necessarily of a 



Fig. 148. — Motor Areas of Dog's Brain 

 (Stewart). 



n, Neck ; /./., fore-limb ; h.l., hind-limb ; t, tail ; 

 /, face (the position here assigned to the 

 facial muscles is unusual, it is generally more 

 laterally situated, and farther forward) ; c.s., 

 crucial sulcus ; e.m., eye movements ; p, dila- 

 tation of the pupil in both eyes, but especially 

 in the opposite eye. 



