vii THE MEDULLA OBLONGATA 413 



to ascertain the extent of the centre which gave rise to these 

 general convulsions. According to him it extends from the bulb 

 to the mid-brain. But Owsjannikow (1875) was able by a better 

 method to show that in the rabbit the centre on which the spread 

 of the convulsions depends is seated in the lower third of the 

 bulb, and has an area of some 6 mm., measured from the tip of 

 the calamus. He evoked the spasm by reflex stimulation of the 

 bulb, using electrical stimulation of a hind-limb of the rabbit. 



After dividing the bulb, by a transection 6 mm. above the tip 

 of the calamus scriptorius, it was possible with a given strength of 

 stimulus to provoke reflex movements in the four limbs of the 

 animal ; but if the section of the bulb were made lower down, the 

 convulsions were only partial, on one or both sides. 



It seems to us probable that while in the higher vertebrates 

 the formatio reticularis normally presides over respiratory rhythm, 

 under abnormal conditions the excitation that affects it directly or 

 reflexly may spread to other skeletal muscles. On this theory the 

 collection of motor cells scattered over this region would deserve 

 the physiological name of general motor centre. 



IX. The medulla oblongata and pons Varolii have other 

 important functions. 



We know that the movements of locomotion are started by 

 voluntary impulses, but once set going they can be continued 

 mechanically, without attention on the part of the subject. This 

 shows that the organs which execute and co-ordinate the move- 

 ments of walking are anatomically distinct from those which 

 control the voluntary impulses proper. That man and many other 

 vertebrates do not walk from birth, and need a long education to 

 acquire the power, is due to the fact that at birth the nerve- 

 centres which subserve locomotion are incompletely developed. 



Physiological experiments show that the centre for progression 

 lies in the bulbo-pontine region. Kedi (1810) first observed that 

 land tortoises can crawl after the brain has been removed. Fontana 

 confirmed this observation, but Rolando failed, probably because 

 he extirpated the bulb also. Fano repeated the experiments with 

 marsh tortoises in our laboratory (1884). He found that if the 

 entire brain, with the exception of the bulb, were destroyed these 

 animals began, after a short time, to exhibit unwonted locomotor 

 activity, either continuous or periodical, and accompanied by 

 movements of the neck and tail. The front limbs became more 

 active than the hind-limbs. The curve of progression shows that 

 such animals do not move in a straight line, but follow an irregular 

 course, and sometimes make circus movements in one or the other 

 direction, not apparently due to any asymmetry of lesion (Fig. 

 218). Locomotion is periodical, not continuous, when the tortoise 

 was not properly awake from its winter sleep, when much blood 

 had been lost at the operation, or when the central activities are 



