The superficial nerves are of two classes, being partly derived from the cervical plexus, partly from the portio dura.
The cervical plexus sends its superficial branchings in three directions : the mastoid and auricular pass upward ; the anterior cervical runs forward ; the supra-clavicular and super acromial, as their names denote, descend more or less obliquely.
The mastoid, originating from the second cervical nerve, winds upwardly across the sple nius, and almost parallel with the posterior edge of the sterno-mistoid, which it crosses in its ascent. It pierces the fascia soon after its origin, and becomes subcutaneous. Its distri bution is entirely to the skin of the mastoid and occipital regions. The auricular, rising from the second and third cervical nerves by a trunk, common to it with the anterior cervical, di rectly pierces the fascia, loops round the .pos terior edge of the sterno-mastoid, and ascends across its surface (the fascia] sheath intervening) toward the angle of the jaw; where, after sup plying twigs to the integuments over the pa rotid gland, it divides into terminal branches, which are distributed to the external and in ternal surfaces of the auricle and to the adjoin ing integument, in a manner which need not be particularised in the present article. In crossing the sterno-mastoid it is parallel to the external jugular vein, and behind it. The anterior cervical rises in common with the last, and pierces the fascia in its company ; bends at right angles across the sterno-mastoid muscle, and is itself crossed by the external jugular vein. On arriving at the edge of the muscle, it di vides into many twigs, which, traversing the platysma at several spots, distribute themselves to the skin of the anterior triangle of the neck, and to that of the adjacent part of the digastric space. This nerve, where crossed by the external jugular vein, gives one or two tninute twigs, which follow its direction toward the angle of the jaw.
The supra-clavicular and super-acromial are the two superficial branches in which the plexus terminates: as they descend, they di vide into a lash of twigs, i.vhich diverge in the posterior triangle of the neck, and at various heights pierce its fascia, become subjacent to the platysma, and contribute to supply it. Their ultimate bmnching takes a very wide range: the inner filaments obliquely cross the clavicular origin of the sterno-mastoid ; the outer, the anterior fibres of the trapezius; the middle ones, the clavicle itself; and are dis tributed, in their respective regions, to the in teguments of the scapula, shoulder, chest, and swrnu m.
The branch from theportio tiara, which enters the neck, is the lower division of its cervico facial part. From near the angle of the jaw, where it traverses the fascia, it passes toward the hyoid bone, and supplies the platysma from its deeper side. Some of these twigs, approaching the cutaneous surface of the muscle in the anterior triangle of the neck, communic-ate with filaments of the anterior cer vical nerve.
1. lliesiol region if the neck.—This presents different relations, as considered above or below the level of the os hyoides.
Above the os hyoides, and extending from the body of that bone to the symphysis of the lower jaw, is the narrow space vvhich sepamtes the anterior bellies of the digastric muscles. It is an elongated triangle, broadest below—where the tendons of the digastrics are kept apart by the body of the hyoid bone—having its apex above, where these, having expanded into the fleshy anterior bellies, are infixed side by side at the median line of the jaw. The platysmata in their cellular sheath cover this space, and sometimes decussate across it with each other. The cervical aponeurosis likewise extends over it, adhering to its bony limits, and strength ened by the tendinous slip, wh.ich is derived from the digastric. Deeper than the digastrics are seen the fibres of the mylo-hyoid muscles, meeting in the median raphe, which runs along the space. The natural direction of this raphe is almost antero-posterior, and that of the fibres which meet in it almost horizontally transverse: but when (as in any opemtion on this part of the neck) the head is thrown back and the chin elevated, the raphe presents a considerable downward slope, and the fibres of the mylo hyoid have a corresponding obliquity. The same observation applies to the deeper fibres which course from the tubercles within the sym physis to the body of the hyoid bone--those, namely, of the genio-hyoid and genio-hyo-glos sal muscles. This little region can hardly be said to have any special surgical relations; it contains neither vessels nor nerves of size ;its injuries only assume importance when they extend beyond it into the adjoining digastric space; its diseases derive no peculiarities from their situation, and for the most part belong to the integuments, which are vascular, highly folliculated, and in the male densely bearded : sycosis often extends to them, and they are a frequent seat of sebaceous tumours.