UN THE VAGUS NERVES OF HYRAX CAPENSIS. 149 



8. On the Vagus and Syinpatlietic Nerves o£ Hyrax capensis. 

 By Chahles F. Sonntag, M.D., F.Z.S., Anatomist to 

 the Societj^ 



[Received Januavy 23, 1921 ; Read February 21, 1922.] 

 (Text-fig-nres 6-8.) 



The present paper is based on the examination of several speci- 

 mens of Ilyrax capensis, both immature and fully adult, which 

 died in the Society's Gardens. Variations were observed in the 

 branches of their vagus and sympathetic nerves ; and the con- 

 ditions present in some of the animals are more complex than 

 those already described in my papers on the Marsupialia (3, 4) 

 and Edentata (5). They are also more complex than those in 

 many animals belonging to other orders. 



Tlie anterior cervical parts of the nerves are placed deeply, and 

 it is necessary to remove the wide ascending rami of the mandible 

 to gain access to them and their branches. 



In all examples the cervical parts of the vagus and sympathetic 

 nerves are fused on both sides to form vago-sympathetic cords, 

 the union taking place at the level of the middle of the thyroid 

 cartilage. The cords are resolved again into their component 

 elements at the root of the neck, but the separation is usually 

 higher on the left side. After they have parted, however, 

 bi'anches of communication may run between them. 



The Vagus Nerves. 



Course : — As it emerges from the foramen lacerum posticum 

 each vagus has the usual relations to the glosso-pharyngeal, spinal 

 accessory and liypoglossal nerves, and it communicates vvith them 

 and the superior cervical ganglion by well-marked branches 

 (text-fig. 6. Cix, Cxi, Cxii and S.O.G). No ganglion nodosum is 

 present in the neck, as in Tamandua tetradactyla (4), or within 

 the foramen lacerum posticum. It then courses postero-mesially, 

 gives off communicating branches to the cervical plexus (C.C.P) 

 and unites with the cervical sympathetic to form the vago- 

 sympathetic cord (V-S) at the level of the middle of the thyroid 

 cartilage. And the nerve up to this point is internal to the 

 mandible. The vago-sympathetic cords break up again in the 

 posterior third of the neck; the vagus half runs still postero- 

 mesially and enters the thorax. Owing to the high level reached 

 by the heart and aorta the first part of the inti'a-thoracic course 

 is short, but the calibre of the left nerve remains thicker than 

 that of the right one. 



IBehind the roots of the lungs the vagi are united by a sinuous 

 cord which is as thick as the left vagus (text-fig, 7, hr), and the 

 nerves emerge again from its extremities, sc the ai-rangement is 

 H-shaped. The left vagus is replaced by right and left branches. 



