102 EXERCISE XVI 



YI. ii. The same as given above in § IV, i, but with addition of severance 

 of 1st cervical nerve by clearing left side of arch of atlas and cutting the nerve 

 as it emerges from that bone. 



VI. iii. Take the thread which was left loosely looped round the dorsal 

 branch of great auricular nerve in § VI, i, of the procedure. Draw it steadily 

 tight upon the nerve, crushing the latter by this ligation. 



While this is done your colleague observes the pinna ; probably the 

 pinna reflex is evoked. 



Turn to the dorsal neck wound ; remove the swab ; pass the small brass 

 hook carefully under the dorsal root, and, drawing the root slightly away from 

 the ventral, sever the dorsal root with fine-pointed scissors, not injuring the 

 ventral in so doing. 



Place another thread ligature round the dorsal branch of great auricular 

 nerve, a millimetre central to the previous one. Tighten the second ligature 

 in the same manner as the first, observing the pinna, as before. No reflex 

 response ensues. 



Expose the great auricular nerve on the right side, repeating the whole 

 of the procedure § VI, i, on that side. 



Turning to the dorsal neck wound, incise the dura mater of the spinal 

 cord longitudinally in the mid-line, taking care not to injure the cord itself. 

 Open the dura freely on the right side. The fan-shaped set of filaments of the 

 dorsal root of right 2nd cervical nerve are thus exposed. Make out ventrally 

 to them the smaller ventral root. 



Evoke the pinna reflex of right side by ligating tightly the dorsal division 

 of great auricular, as you did on the left. 



Carefully pass the small brass hook under ventral root (PL VIII, fig. 4) 

 of right 2nd cervical, avoiding engaging in the hook any filaments of the dorsal 

 root. Drawing the ventral root slightly forward and laterally, sever it with 

 fine scissors without harming the dorsal root. Cover the wound with a warm 

 moist swab. 



Pass a ligature round dorsal branch of great auricular, and draw it tight 

 proximal to the former ligature. The reflex response is still elicited by the 

 crushing of the nerve. D 



ANNOTATION 



Ohs. 75. In regard to this and Obs. 72 Obs. 76, 77. The exercise uses a specific 



(exerc, XV) consult Brain, vol. xxxviii, skin-reflex to test the Magendie ' law '. For 



p. 210 (Sherrington), 1915, and H. Pieron, account of the pinna reflexes and of the 



Compt. rend. d. I. Soc. d. Biologic, p. 410 : head-shake reflex protecting auditory meatus 



Paris, 1917; La Presse M^dicale, Paris, see Jnl of Physiol, vol. li, -p. 404:, 1917. 

 Feb. 18, 1918. 



