The portio dura nerve passes out of the stylo-mastoid foramen and enters the substance of the parotid gland. At its exit from the foramen the nerve sends off three small branches, the posterior auricular, the digastric, and the stylo-hyoid.
The posterior auricular nerve passes off from the anterior part of the portio dura ; it passes upwards and forwards round the anterior sur face of the mastoid process, and is joined by the great auricular nerve of the cervical plexus; it then becomes superilcial, accompanies the artery of the same name, and is distributed to the ear and side of the head.
The digastrie nerve passes backwards and is distributed by several filaments to the posterior belly of the dic,eistric muscle. It sends an anasto moue filanient to the glosso-pharyngeal nerve.
The stylo-hyoid nerve arises often from a common trunk s%ith the preceding; it enters the stylo-hyoid muscle after passing along its supe rior border.
After the portio dura has given off the above mentioned branches it passes forwards through the substance of the parotid gland below the meatus auditorius externus ; it then crosses over the posterior auricular artery and the styloid process, the external jugular vein and the ex ternal carotid artery, and before reaching the ramus of the jaw it divides into two branches, the tempero-facial and the cervico-faciul, which diverge from each other.
The teniperofacial division passes upwards and forwards in the substance of the parotid, forming with the trunk of the facial nerve an arch, the concavity of which is above ; it then crosses the neck of the lower jaw and receives sit this point one and sometimes two branches from the auriculo-temporal branch of the in ferior maxillary nerve. The teinpero-facial nerve then breaks up into a number of branches vvhich ana.stomose and form arches, from the
convexities of which proceed a number of di verging filaments, some of which pass upwards and others forwards, emerging from beneath the parotid, to be distributed to the muscles of the face.
The cervico-facial division is smaller than the preceding ; it takes the same direction as the trunk of the nerve, passing dovviiwards and forwards in the substance of the parotid ; at the angle of the jaw it divides into three or four branches ; these subdivide into secondary branches, some of which pass forwards to sup ply the inuscles of the lower part of the face, while others are distributed to the upper part of the cervical region.
Lymphatic glands.—Several lymphatic glands are found imbedded in the superticial surface, and in the substance of the parotid. These may readily be distinguished from -the tissue of the parotid by their red colour. They are not uncommonly the seat of disease, and if their removal becomes necessary the 'opera tion may be done without much difficulty and without great risk of wounding any important textures. But a slig,ht consideration of the deep connexions of the parotid and of its close relations to the many important parts which pass through it, and by which it is surrounded, will be sufficient to convince the surgeon that the removal of this gland cannot be effected without extreme difficulty and danger, and that it must necessarily be attended by injury to some of the important parts in this region. The division of the facial nem, and conse quent palsy of the face, may be looked upon as one of the most serious and certain conse quences of an attempt to excise the parotid.
( George Johnson.)