SYMPATHETIC NERVES OF HYRAX CAPENSIS. 151 



The superior laryngeal nerve (b) is replaced by a strong cord 

 which unites with one of tlie divisions of the recurrent nerve. 

 This coxtI gives off internal laryngeal (i.l.n), two external lai-yn- 

 geal (e.l.n), two thyroid {t.y.n), and three external pharyngeal 

 (a) nerves. Small branches {v.n) accompany the common carotid 

 artery. The internal laryngeal branch enters the larynx through 

 the thyro-hyoid interval. 



The left recurrent nerve (e) is given off in the common position. 

 It encircles the aortic arch and runs a,ntero-laterally through the 

 neck. In the middle of the neck it shows a fusiform expansion 

 (E) and divides into a mesial nerve (R.L.N), which is the true 

 inferior laryngeal nerve, and a lateral cord (C) which unites with 

 the superior laryngeal nerve to form a loop, whose upper pai-t 

 has been described above. Numerous tracheal (TN) and (Esopha- 

 geal nerves (ON) are given off. They form plexuses of which the 

 tracheal one is the more superficial. And the oesophageal plexus 

 anastomoses with the oesophageal branches of the right recurrent 

 nerve (d). The latter also forixis a loop with the right superior 

 laryngeal nerve, but there is no fusiform expansion. And both 

 recurrent nerves give off cardiac branches (C.N) which are thicker 

 and more numerous on the left side. 



In some specimens these loops are absent, and there is no 

 external communication between the superior and recurrent 

 laryngeal nerves. 



The existence of anastomoses between the laryngeal nerves in 

 Man has long been known. And Landois and Stirling (2) sum- 

 marised our knowledge as follows : — " A connecting branch runs 

 from the superior laryngeal to the inferior (the anastomosis of 

 Galen), which occasionally gives off sensory branches to the upper 

 half of the trachea (sometimes to the larynx ?) ; perhaps also to 

 the oesophagus {Longet), and sensory fibres (?) for the muscles of 

 the larynx supjalied by the recurrent laryngeal. According to 

 FranQois Frank, sensory fibres pass by this anastomosis from the 

 recui'rent into the superior laryngeal. According to Waller and 

 Burckhard, the motor fibres of both laryngeal nerves are all de- 

 rived from the accessorius, while Chauveau maintains that the 

 crico-thyroid is an exception." In a recent paper Dilworth (1) 

 described and figured a well- mai^ked bi^anch running between the 

 recurrent and internal laryngeal nerves, and says: " . . . . the 

 laryngeal nerves are really a plexus of nerves. Just as the vagus 

 breaks up into its various plexus'es in the body, it does the same 

 in the larynx. It is a highly modified plexus. I would further 

 suggest tliat it ai-ose by the larynx separating a strand of fibres 

 from the vagus — that this strand is represented by the continuovKS 

 nerve joining the internal and recurrent laryngeal, and that the 

 separation from this strand of further fibres forms the various 

 nerves of the larnyx." The conditions shown in text-fig. 6 sup- 

 port Dilworth's views, and I would extend his views of the origin 

 of the laryngeal nerves from the continuous strand to account for 

 the origin of the tracheal, oesophageal, and thyroid nerves. 



