150 



separate again into two mixed nerves, and pass downwards 

 and backwards. The lower one receives the R. coniniuni- 

 cans from the first spinal sympathetic ganglion [com. 1). 

 They subsequently unite again, and distal to the union a 

 large sensory and motor nerve is given olt', which curves 

 downwards and forwards. This is the R. cervicalis or 

 so-called N. hypoglossus (r. cerv.). It courses at first at 

 the side of the pericardium opposite the junction of the 

 auricle and ventricle, and the upper sensory and the lower 

 motor components are quite obvious. In front, the two 

 components separate out into a dorsal sensory and a 

 ventral motor nerve. Shortly after giving oif the above, 

 the R. ventralis receives a sensory and motor anastomosis 

 from the R. ventralis of the second spinal nerve (r. v. 2^), 

 thus forming the brachial plexus. The compound trunk 

 (r. V. 1) then courses downwards and slightly backwards, 

 and gives off a motor nerve in front and behind to the 

 muscles of the pectoral girdle (?'. i'. 1^ and r. v. 1^). It 

 now passes through the scapular fenestra (see fig. 8 — 

 indicated by a ring in the chart), in order to reach the 

 external aspect of the pectoral girdle, where the two com- 

 ponents at once separate out into an anterior motor nerve 

 (r. V. 1^) and a posterior sensory nerve (r. v. 1 ), which are 

 distributed to the pectoral fin, the latter to its dorsal 

 region. 



The following nerves arise from the extracranial 

 ganglion : — 



1. R. communicans, b. (r. com. b.). — A large sensory 

 nerve from the extreme dorsal point of the ganglion. It 

 passes forwards over the roof of the skull at the same 

 transverse level as the R. spinosus, b., but external to it. 

 It ultimately passes first outwards and then downwards 

 between the skull and the skin, and is distributed to the 

 latter in the region of the auditory capsule. As the R. 



