PINNA KEFLEXES AND SPINAL ROOTS 101 



The great auricular nerve is thus exposed (PI. VIII, fig. 5) emerging from 

 under anterior border of m. clavio-trapezius and running towards the parotid 

 gland and concha ; the nerve passes forwards and divides just behind the 

 concha of the ear into branches ; some of these twigs turn ventrally, some 

 continue horizontally, but those which slope dorsally are the essential ones for 

 the experiment ; pass a ligature under them and leave it untied. 



Text-fig. 36. Scheme of reflex path used in employing pinna reflex for testing the 

 conduction of afferent root of 2nd cervical nerve and auricularis magnus trunk, viith, the 

 left facial nerve ; 1st, 2nd, 3rd, first, second, and third left cervical nerves ; p, part of parotid 

 gland ; La., levatw auris longus muscle ; g.x, thread loop round great auricular nerve in 

 superficial part of its course (ligation provides stimulus) ; m, muscles of neck covering deeper 

 course of great auricular nerve. Spinal cord and bulb indicated by shaded area. 



Follow the nerve-trunk backward under cephalo-humeralis, cutting through 

 part of this muscle and retracting it laterally to expose the nerve. Just under 

 the muscle the nerve seems to be joined by a nerve, n. accessorius, which 

 crosses it — this crossing is the ' carrefour ' (PI. VIII, fig. 6). Without damaging 

 the great auricular nerve, cut through the accessorius nerve to either side of 

 great auricular itself. Follow the great auricular nerve backward. It lies 

 upon the splenius muscle, and proceeds to dip under levator scapulae ventralis ; 

 the dissection is facilitated by retracting with clip-weight the lateral edges of 

 these muscles. Carefully open up the intermuscular space into which the 

 nerve plunges ; in doing so some bleeding may be caused, but pursue the 

 nerve until a point is reached where the nerve divides into two, a more 

 posterior trunk which passing inwards and backwards joins the 3rd cervical 

 nerve, and an anterior which passes inwards to join the 2nd cervical nerve 

 (PI. VIII, fig. 6). Carefully sever with the scissors the former of these two 

 divisions and when cutting it note the pinna of the ear ; this will probably 

 give a retractive movement ; the movement is a spinal reflex, the motor nerve of 

 the pinna being the 7th cranial. Take pains not to damage in any way the 

 anterior of the two divisions. Remove the retracting clip-weights, replace the 

 skin-flaps over the wound. 



