886 THE MEDULLA OBLONGATA. 



root cells, leading from the segmental nerves of the whole body below 

 the brachial region ; third (Burdach's nucleus), for afferent root cells, leading 

 from all the brachial and cervical nerves. 



The efferent root cell system discharges impulses to various regions of the 

 alimentary secretory epithelium, from mouth to pancreas inclusive (chorda 

 tympani, Jacobson's nerve, and branches of vagus), and the musculature of the 

 alimentary canal from the soft palate along the pharynx and oesophagus to 

 and inclusive of the stomach, 1 including the respiratory diverticulum (larynx, 

 trachea, and lungs), and the tongue. The nucleus ambiguus is the cell group 

 whence arise most, if not all, of the efferent fibres of the glosso-pharyngeal, 

 vagus, and accessory nerves ; the rootlets of the last named are entirely efferent. 

 Cajal 2 has found that some of the axis cylinders from the nucleus ambiguus 

 pass to the rootlets of the crossed glosso-pharyngeal nerve, though the great 

 majority enter the homonymous nerve : the same condition he found in lesser 

 degree to hold in relation to the vagus rootlets. 



In the frog, removal of the encephalon down to the level of the 

 octavus nerve leaves the animal with regular and apparently normal 

 respiratory movement and circulation, but with considerable impairment 

 of its locomotor powers. It rests sprawling with head sunk. It crawls 

 only under obvious external stimulation. 3 Locomotion is easier to 

 provoke than when the transection lies at the caudal end of the fourth 

 ventricle. 4 It will usually, when laid on its back, try to right itself, and 

 usually succeeds. This evidences the existence of geotropic sense and of 

 considerable muscular co-ordination. The co-ordinating action of the 

 frog's myelencephalon on the skeletal musculature, may be likened to that 

 of the ring commissure of Asterias. When placed in the tank upside down, 

 a united action of the five rays soon rights the animal. But if without 

 injury to the individual nerve systems of the several rays, the circum- 

 buccal nerve ring be severed between the adjacent rays, ability to correct 

 the inverted posture is destroyed. 5 The individual action of the rays 

 is vigorous, but they largely neutralise each other's mechanical effect. 

 The inco-ordinate activity fails to arrive at the result attained when 

 due correlation is ensured by the nerve-ring. The actions of the 

 individual rays must therefore, when the nerve-ring is intact, influence 

 each other. The convergence of afferent spinal paths from the skeletal 

 musculature and of paths from the vestibular nerve towards the region 

 which possesses this, co-ordinating influence, is suggestive of their 

 co-operation toward the result. 



The mammal, after similar removal of all encephalon in front of 

 the bulb, still breathes with regularity, and possesses good circulatory 

 adjustments. There is still some degree of co-ordinate movement of 

 progression, but such movement is difficult to provoke. When the 

 transection lies below the junction of the middle and lowest thirds of 

 the fourth ventricle, it becomes in some mammals 6 extremely difficult to 

 evoke by any sensory stimulus a movement in which all four limbs come 

 into play. I would remark that, by this transection, the vestibular 



1 Bichat, " Anat. gen.," Paris, 1812, tome iii. p. 360 ; Budge, Nov. acta phys.-mcd. Acad. 

 nat. curios, 1860, vol. xxvii. 



a "Origen de los nervios vago y glosso faringeo," Madrid, 1895. 



3 Schrader, Arch. f. d. ges. PhysioL, Bonn, 1887, Bd. xli. 



4 Noted in salamander also by Pfliiger, "Die sensorische Functionen des Riicken- 

 raarkes," Berlin, 1852. 



5 G. Romanes, Phil. Trans., London, 1881 ; J. Demoor and Marcellin Chapeaux, Trav. 

 de I. stat. zool. d. ffelder, 1891. 



6 Owsjannikovv, Arb. a. d. physiol. Anst. zu Leipzig, 1874, S. 314. 



