PINNA REFLEXES AND SPINAL ROOTS 99 



atlas, and retract them aside both from atlas and axis. When the ganglion 

 of each side has been seen, clip off with the oblique-jawed cutting bone-pliers 

 the whole overhanging beak of the spinous process of axis. Follow very 

 carefully by dissection with the small scalpel the root of the 2nd cervical 

 nerve of the left side. Follow up the median end of the root, still sheathed 

 in a prolongation from the dura mater, and observe the separation between 

 dorsal root and ventral. There is usually a slight separation into two of the 

 dorsal root in its sheath : this must not be mistaken for the separation between 

 the dorsal root and the smaller ventral root. The latter root lies slightly 

 anterior as well as ventral to the dorsal. 



Having ascertained the distinction between dorsal and ventral root, pass 

 the small brass hook between them to open up their separation (PI. VIII, fig. 4) 

 and then withdraw it. Cover dorsal neck wound with a warm moist swab. 



IV. ii. Test the pinna reflex of the left ear by gently twisting or 

 crumpling the tip of the pinna between finger and thumb. This elicits the 

 reflex, whose response consists in a quick retraction of the pinna and usually a 

 folding back of the free end of the pinna. The motor nerve executive of the 

 response is the 7th cranial. The dorsal root of the 2nd cervical nerve contains 

 a large share of the afferent nerve-fibres which specifically evoke the reflex 

 (see text-fig. 36). 



IV. iii. Follow carefully the nerve-trunk of 2nd cervical of left side 

 laterally from the ganglion, exposing it without dragging on it or on the 

 ganglion, and not actually touching either. It has two (PI. VIII, fig. 3) relatively 

 superficial branches passing laterally over muscle, and a third, a deeper, 

 descending closer to the side of the bone (atlas). It is the deeper branch (PI. 

 VIII, fig. 3) which contains afferent fibres from the pinna : these have passed 

 by way of n. auricularis magnus and are en route to enter the spinal cord 

 by the ganglion and dorsal root of the 2nd cervical nerve. Carefully expose this 

 branch and pass a ligature of coarse thread round it as far from ganglion 

 as practicable. In doing so, despite of all care, you will probably excite the 

 retraction and back-folding reflex of the pinna ; be on the look out for that ; 

 it is the reflex by which you are going to test the conductivity of the spinal 

 nerve-roots. The coarse thread-loop passed round the nerve-branch is for 

 stimulating the nerve mechanically by ligation. Ligate, tightening steadily 

 and rather slowly and watching the while the ipsilateral pinna. Reflex 

 retraction of the pinna will be evoked. 



Place similarly round the nerve a second ligature, close proximal to the 

 former, but leaving it loose for the present. With the fine hook-seeker 

 (PI. VIII, fig. 4) carefully separate the dorsal root of the nerve from the 

 ventral and cut the dorsal root completely through with the small, fine-pointed 



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