560 CRANIAL NERYES. 



The Posterior pulmonary branches, more numerous and larger than the anterior, 

 are distributed on the posterior aspect of the root of the lung ; they are joined by 

 filaments from the third and fourth thoracic ganglia of the sympathetic, and form 

 the posterior pulmonary plexus. Branches from both plexuses accompany the 

 ramifications of the air-tubes through the substance of the lungs. 



The CEsopkageal branches are given off from the pneumogastric both above 

 and below the pulmonary branches. The latter are the more numerous and 

 largest. They form, together with branches from the opposite nerve, the ceso- 

 phageal plexus. 



The Gastric branches are the terminal filaments of the pneumogastric nerve. 

 The nerve on the right side is distributed to the posterior surface of the stomach, 

 and joins the left side of the cceliac plexus, and the splenic plexus. The nerve 

 on the left side is distributed over the anterior surface of the stomach, some 

 filaments passing across the great cul-de-sac, and others along the lesser curvature. 

 They unite with branches of the right nerve and sympathetic, some filaments 

 passing through the lesser omentum to the left hepatic plexus. 



(3.) SPINAL ACCESSORY NERVE. 



The SPINAL ACCESSORY NERVE consists of two parts ; one, the accessory part 

 to the vagus, and the other the spinal portion. 



The accessory part, the smaller of the two, arises by four or five delicate 

 filaments from the lateral tract of the cord below the roots of the vagus ; these 

 filaments may be traced to a nucleus of gray matter at the back of the medulla, 

 below the origin of the vagus. It joins, in the jugular foramen, with the upper 

 ganglion of the vagus by one or two filaments, and is continued into the vagus 

 below the second ganglion. It gives branches to the pharyngeal and superior 

 laryngeal branches of the vagus. 



The spinal portion, firm in texture, arises by several filaments from the lateral 

 tract of the cord, as low down as the sixth cervical nerve ; the fibres pierce the 

 tract, and are connected with the anterior horn of the gray crescent of the cord. 

 This portion of the nerve ascends between the ligamentum denticulaturn and the 

 posterior roots of the spinal nerves, enters the skull through the foramen magnum, 

 and is then directed outwards to the jugular foramen, through which it passes, 

 lying in the same sheath as the pneumogastric, separated from it by a fold of the 

 arachnoid, and is here connected with the accessory portion. At its exit from the 

 jugular foramen, it passes backwards behind the internal jugular vein, and descends 

 obliquely behind the Digastric and Stylo-hyoid muscles to the upper part of the 

 Sterno-mastoid. It pierces this muscle, and passes obliquely across the sub- 

 occipital triangle, to terminate in the deep surface of the Trapezius. This nerve 

 gives several branches to the Sterno-mastoid during its passage through it, and 

 joins in its substance with branches from the third cervical. In the sub-occipital 

 triangle it joins with the second and third cervical nerves, assists in the formation 

 of the cervical plexus, and occasionally of the great auricular nerve. On the 

 front of the Trapezius, it is reinforced by branches from the third, fourth, and 

 fifth cervical nerves, joins with the posterior branches of the spinal nerves, and is 

 distributed to the Trapezius, some filaments ascending and others descending in 

 its substance as far as its inferior angle. 



4. MIXED NERVES. 



The Pneumogastric and Spinal Accessory Nerves, which constitute this sub- 

 division, have already been described in connection with the Eighth Pair, of which 

 they form part. 



For fuller details concerning the Cranial Nerves, the student may refer to F. Arnold's "Icones 

 Nervorum Capitis." 



