THE PNEUMO-GASTKIC NERVE. 265 



and the spinal accessory nerve ; and there is sometimes a filament connecting it with 

 the petrosal ganglion of the glosso-pharyngeal. 



The lower ganglion of the pneumo-gastric forms connections with the hypo- 

 glossal nerve, with the superior cervical ganglion of the sympathetic, and with the 

 loop between the first two cervical nerves. 



B. Branches of distribution. 



The recurrent or meningeal branch, arises from the upper ganglion of the 

 pneumo-gastric, and passes backwards through the jugular foramen to be distributed 

 to the dura mater in the posterior fossa of the base of the skull. 



The auricular branch (nerve of Arnold) is given off from the ganglion of the 

 root, and, after receiving a filament from the petrosal ganglion of the glosso-pharyn- 

 geal nerve, runs backwards along the outer boundary of the jugular foramen to an 

 opening near the root of the styloid process. It then traverses the substance of the 

 temporal bone, crosses the acqueduct of Fallopiuson its inner side about 4 mm. from 

 the lower end, forming here a communication with the facial nerve, and finally 

 emerges between the external auditory meatus and the mastoid process, where it 

 divides into two parts, the one of which joins the posterior auricular nerve, while the 

 other is distributed to the skin of the back of the pinna, and the lower and back part 

 of the auditory canal. 



Varieties. In rare instances, absence of the auricular branch has been observed, or of the 

 communication with the facial nerve. The auricular branch occasionally passes entirely into 

 the facial trunk, and in that case its fibres are probably conveyed to the external ear through 

 the posterior auricular nerve. 



The pharyngeal branch, often represented by two or even more offsets, and 

 composed mainly of fibres prolonged from the accessory part of the spinal 

 accessory nerve, leaves the upper part of the ganglion of the trunk of the 

 vagus. It courses inwards over the internal carotid artery, and divides into 

 branches which, conjointly with those derived from the glosso-pharyngeal and 

 the sympathetic, form the pharyngeal plexus. This plexus often contains one or 

 more small ganglia, and from it filaments pass to the muscles and mucous mem- 

 brane of the pharynx. The motor fibres are conveyed to the plexus by the pharyn- 

 geal branch of the vagus, but they are probably derived from the bulbar part of the 

 spinal accessory nerve (see p. 270) ; the levator palati and azygos uvulae muscles are 

 also supplied by a branch from this source. 1 One slender branch (lingual branch of 

 the vagus Luschka) descends from the pharyngeal plexus, receiving its fibres from 

 the pharyngeal branches of both the glosso-pharyngeal and pneumo-gastric nerves, 

 and joins the hypoglossal nerve as that turns round the occipital artery. 



Superior laryngeal nerve. This branch springs from the middle of the 

 ganglion of the trunk of the vagus, and inclines forwards on the inner side of the 

 internal carotid artery towards the larynx. It is joined by filaments from the upper 

 cervical ganglion of the sympathetic and from the pharyngeal plexus, and speedily 

 divides into two branches which are distinguished as external and internal laryngeal. 



The external laryngeal branch, the smaller of the two, runs downwards and for- 

 wards beneath the depressor muscles of the hyoid bone to the crico-thyroid muscle 

 in which it ends. It receives a filament from the upper cervical ganglion of the 

 sympathetic, and it gives off twigs to the inferior constrictor muscle of the pharynx, 

 as well as generally a cardiac branch which joins the superior cardiac branch of the 

 sympathetic. 



The internal laryngeal branch is continued to the interval between the hyoid 



1 The middle constrictor of the pharynx would appear in the monkey to be partly supplied by glosso- 

 pharyngeal fibres (Beevor & Horsley, op. cit. on p. 270). 



