PNEUMO-GASTR1C XERVE. 621 



Inferiorly, it forms a single trunk in front of the oesophagus, and is spread 

 out on the anterior or superior 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 development. The recurrent direction of the inferior laryngeal 

 branches in all probability arises from the extreme shortness or rather absence of the 

 neck in the embryo at first, and from the branchial 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 circumstance that one recurrent laryngeal nerve passes round the 

 subclavian artery, and the other round the aorta, is seen to arise from an originally 

 symmetrical disposition, when it is remembered that the innominate artery and the 

 arch of the aorta are derived from corresponding arches of the right and left sides. 

 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 sub- 

 sequent growth. 



BRANCHES OF THE PNEUMO-GASTRIC NERVE. 



Some of its branches serve to connect the pneumo-gastric with other 

 nerves, and others are distributed to the muscular substance or the mucous 

 lining of the organs which the nerve supplies. The principal con- 

 necting branches of this nerve are derived from the ganglia. In the 

 different stages of its course branches are supplied to various organs aa 

 follows. In the jugular foramen, a branch is given to the ear ; in the neck, 

 branches are furnished successively to the pharynx, the larynx, and the 

 heart ; and in the thorax, additional branches are distributed to the heart, 

 as well as to the lungs and the oesophagus. Terminal branches in the 

 abdomen are distributed to the stomach, liver, and other organs. 



CONNECTING BRANCHES AND AURICULAR BRANCH. 



Connections between the upper ganglion of the vagus nerve and the spinal accessory, 

 glosso-pharyngeal, and sympathetic nerves. The connection with the spinal accessory 

 is effected by one or two filaments. The filament to the petrous ganglion of the 

 glosso-pharyngeal is directed transversely ; it is not always present. The communi- 

 cation with the sympathetic is established by means of the ascending branch of the 

 upper cervical ganglion. 



The auricular branch is continued to the outer ear. Arising from the ganglion of 

 the root, this branch is joined by a filament from the glosso-pharyngeal nerve, and 

 then turns backwards along the outer boundary of the jugular foramen to an opening 

 near the styloid process. Next, it traverses the substance of the temporal bone, 

 crossing the aqueduct of Fallopius, about two lines from the lower end, and, reaching 

 the surface between the mastoid process and the external auditory meatus, is distri- 

 buted to the integument of the back of the ear. On the surface it joins with a twig 

 from the posterior auricular branch of the facial nerve. 



Connections of the second ganglion with the hypoglossal, sympathetic, and spinal 

 nerves. This ganglion is connected by filaments with the trunk of the hypoglossal, 

 with the upper cervical ganglion of the sympathetic, and with the loop formed between 

 the first two cervical nerves. 



PHARYNGEAL BRANCH. 



The pharyngeal branch arises from the upper part of the ganglion of the 

 trunk of the nerve. In its progress inwards to the pharynx this nerve 

 crosses in some cases over, in others under the internal carotid artery ; and 



