264. 



THE CRANIAL NERVES. 



posterior pulmonary plexus, whence it descends along the oesophagus, and takes part 

 in the formation of the oesophageal plexus. Inferiorly, it forms a single trunk in 

 front of the oesophagus, and is spread out on the anterior surface of the stomach. 



There are various circumstances in the distribution of the pneumo-gastric nerves which at 

 first sight appear anomalous, but which are explained by reference to the process of develop- 

 ment. The recurrent direction of the inferior laryngeal branches arises from the extreme 

 shortness or rather absence of the neck in the embryo at first, and from the primitive arterial 

 arches having- originally occupied a position at a higher level than the parts in which those 

 branches are ultimately distributed, and having dragged them down as it were in the descent 

 of the heart from the neck to the thorax. The recurrent direction may therefore be accepted 

 as evidence of the development of those nerves before the occurrence of that descent. The 

 passage of one recurrent laryngeal nerve round the subclavian artery, and of the other round 

 the aorta, arises from the originally symmetrical disposition in which the innominate and sub- 

 clavian arteries on the right side, a,nd the arch of the aorta on the left, are derived from cor- 

 responding arches. The supply of the back of the stomach by the right pneumo-gastric nerve, 

 and of the front by the left nerve, is connected with the originally symmetrical condition of the 

 alimentary canal, and the turning over of the stomach on its right side in its subsequent 

 growth. 



BRANCHES. Some of the branches of the pneumo-gastric serve to connect this 

 with other nerves, but the larger number are distributed to various parts of the cir- 



Fig. 180. DIAGRAM OF THE ROOTS AND COMMUNI- 

 CATING BRANCHES OP THE PNEUMO-GASTRIC AND 



NEIGHBOURING NERVES. (From Sappey, after 

 Hirschfeld and Leveille.) 



1, facial nerve ; 2, glosso-pharyngeal with the 

 petrosal ganglion ; 2', connection of the digastric 

 branch of the facial nerve with the glosso-pharyngeal 

 nerve ; 3, pneumo- gastric, with its two ganglia ; 

 4, spinal accessory ; 5, hypoglossal ; 6, superior 

 cervical ganglion of sympathetic ; 7, 7, loop of union 

 between the first two cervical nerves ; 8, carotid 

 branch of sympathetic ; 9, nerve of Jacobson (tym- 

 panic), given off from the petrosal ganglion ; 10, 

 its cavotico-tympanic filaments ; 11, twig to Eusta- 

 chian tube ; 12, twig to fenestva ovalis ; 13, twig to 

 fenestra rotunda ; 14, small supei'ficial petrosal 

 nerve ; 15, large superficial petrosal nerve ; 1(5, otic 

 ganglion ; 17, auricular branch of pneumo-gastric ; 

 18, connection of spinal accessory with pneumo- 

 gastric ; 19, union of hypoglossal with first cervical 

 nerve ; 20, union between the sterno-mastoid branch 

 of the spinal accessory and that of the second 

 cervical nerve ; 21, pharyngeal plexus ; 22, superior 

 laryngeal nerve ; 23, external laryngeal ; 24, middle 

 cervical ganglion of sympathetic. 



culatory, respiratory and digestive systems. 

 The special connecting branches arise 

 from the two ganglia of the nerve. The 

 branches of distribution arise from the 

 nerve in the several stages of its course 

 as follows : In the jugular foramen, one 



small branch is given to the dura mater, and another to the ear ; in the neck, 

 branches are furnished successively to the pharynx, the larynx, and the heart ; in the 

 thorax, additional branches are supplied to the heart, as well as offsets to the peri- 

 cardium, lungs and oesophagus ; and in the abdomen, its terminal branches are dis- 

 tributed to the stomach, liver, and other organs. 

 A. Branches of communication. 



The upper ganglion of the pneumo-gastric nerve receives a twig from the 

 superior cervical ganglion of the sympathetic ; one or two filaments pass between it 



