56i THE CRAXIAL NERVES. 



the nerves of the right and left sides, while they lie in contact with the 

 oesophagus. 



Gastric branches. — The l^ranches distributed to the stomach 

 {fiastric ncrvrH) are the terminal branches of both pneumogastric nerves. 

 The nerve of the left side, on arriving in front of the oesophagus, oppo- 

 site the cardiac orifice of the stomach, divides into many branches: the 

 largest of these extend over the fore part of the stomach ; others lie 

 along its small curvature, and unite with branches of the right nerve 

 and the sympathetic ; and some filaments are continued between the 

 layers of the small omentum to the hepatic plexus. The right pneumo- 

 gastric nerve descends on the back of the gullet to the stomach, and 

 distributes branches to the posterior surfoce of the organ : a part of 

 this nerve is continued from the stomach to the left side of the coeliac 

 plexus, and to the splenic plexus of the sympathetic. 



Varieties. —The pneumogastric nerve of the right side has been found in front 

 of the sheath of the great cervical vessels (Quain). In several instances the 

 origin of the descendens noni has been transferred to the trunk of the pneumo- 

 gastric. Turner, who has recorded such cases, mentions also one in -which the 

 entire trunk of the hypoglossal nerve was intimately connected with the pneumo- 

 gastric as low as the posterior belly of the digastric muscle. The superior 

 laryngeal nerve has fi'equently been seen to give branches to the thjTo-hyoid 

 and sterno-hyoid muscles (Meckel, Reid, Cloquet, Krause). The recurrent 

 larj-ngeal in rare cases supplies the crico-thyroid muscle (Reid). This nerve also, 

 in those cases in which the right subclavian artery arises from the left side of the 

 aortic arch, passes directly inwards to the larynx in the neck, and is not hooked 

 downwards towards the thorax by the subclavian. This abnormality is explained 

 developmentally by the origin of the subclavian from the right aortic root 

 posteriorly, and by the closure of the fourth branchial arch, as well as of the 

 fifth, upon the right side. 



SiBiMARY. — The pneumogastric nerves supply branches to the upper 

 part of the alimentary canal, viz., the pharynx, oesophagus, and stomach 

 Avith the liver and spleen ; and to the respiratory passages, namely, the 

 larynx, trachea, and its divisions m tb.e lungs. These nerves give 

 branches likewise to the heart and great vessels by means of their com- 

 munication with the cardiac plexus. Each pneumogastric nerve is 

 connected with the following cranial nerves — the spinal accessor}-, 

 glosso -pharyngeal, facial, and hypoglossal : also, with some spinal 

 nerves ; and with the sympathetic in the neck, thorax, and abdomen. 



III. SPINAL ACCESSORY NERVE. 



The spinal nerve accessory to the vagus, or, as it is shortly named, 

 the spinal accessory nerve, consists of two parts : one (accessory) joins 

 the trunk of the pneumogastric ; the other (spinal) ends in branches 

 to the sterno-mastoid and tra^iezius muscles. 



Surface attacliment. — The accessory nerve arises by a series of 

 roots, the upper of which are attached to the side of the medulla below" 

 those of the pneuuK^gastric, while the remainder arise from the lateral 

 column of the cervical portion of the cord as low down as the sixth or 

 seventh pair of nerves. The lowest spinal roots are attached to the 

 middle of the lateral column ; the highest spinal roots arise close to the 

 posterior nerve roots. 



Deep origin. — The upjier roots pass inwards to a nucleus which 

 lies, on each side, at the back of and close to the central canal. It 

 contains large nerve-cells, and is continuous, above, with the column of 



