Page:Muscles and Regions of the Neck.djvu/12

10 the prolongation which it sends downward on the scaleni; and which partly fixes itself to the rib around the attachments of those muscles, partly extends itself, as a strong infundibulum on the brachial plexus and subclavian vessels. From this—their fascial sheath—an horizontal slip detaches itself and passes forward to the posterior surface of the clavicle, where it fixes itself by two laminæ; the upper of these is inserted just above the attachment of the sub-clavius muscle, while the lower is continued into the sheath which that muscle derives from the coraco-costal fascia. The horizontal process separates the cavity of the axilla from the lower triangle of the neck, and the vaginal prolongation, contracting as it descends, becomes lost in the sheath of the axillary vessels.

Finally, as these various layers of fascia attach themselves about the inlet of the thorax, (the sub-hyoid part of the cervical aponeurosis in front, and the pre-vertebral behind,) they are connected to one another and to the large vascular and mucous canals, which traverse that passage, by certain horizontal processes of fibrous membrane, which constitute together a kind of diaphragm, or cervico-thoracic septum. Viewed from below this would seem a vaulted membrane, overarching the tops of the pleuræ, and giving infundibular passage to the great arterial and venous trunks and to the trachea; viewed from above it would present the various deep implantations of the cervical fascia, and a surface without aperture or breach of continuity, prolonging itself in several directions round the canals, which it thus indirectly transmits. The obvious use of these arrangements is to supply adequate resistance to the atmospheric pressure, which, were it not borne off by the tension of these fasciae, would at each inspiratory effort tend to flatten the trachea, or to rush through the upper strait of the thorax. Allan Burns, who in this country first drew attention to the importance of the cervical fascia, carefully illustrates its functions in health, and the inconveniences which accompany its destruction. (Op. cit.)

The posterior parts of the neck having been described in a previous article (see ), the present will be restricted to an account of its anterior aspect.

The cervical vertebræ (by their bodies, intervening fibro-cartilaginous discs, and transverse processes), together with the anterior and lateral vertebral muscles, already described, compose the skeleton and supporting fabric of this region; the anterior fibres of the trapezii, as they descend on either side to the inner edge of the acromio-clavicular arch, form its lateral boundaries; the larynx and trachea (covered by their own extrinsic riband-like muscles, and partly covering the pharynx and œsophagus) separate the nearly symmetrical halves of the neck by constituting along its median line a marked columnar relief, in the recesses beside which lie the great cervical vessels; the base of the skull and the oblique line of the jaw are the upper limits of the region; the clavicle (just behind which the great vascular and nervous trunks of the upper extremity course) bounds it below; the skin, the platysma myoides (in its cellular covering), and the cervical aponeurosis are stretched across it as general investments; while the last-named fascia ensheathes the various parts by special processes from its deeper surface.

Thus, in general terms, the structure of the neck may be described; but, for the more precise and particular account, which the importance of its anatomy renders necessary, a division of it into spaces of small extent is convenient. The arrangement, which I propose following, differs but little from that usually adopted, and, perhaps, somewhat exceeds it in precision.

The upper limits of the neck having been stated as the oblique line of the jaw and the base of the skull (which parts, as we shall presently see, are brought into relation by the attachments of the constrictor pharyngis superior), our highest region has in that direction these parts for its boundary, and extends below as far as the curve of the muscle, from which it is named the digastric space.

A small space that can hardly be referred to the digastric,—from which it is separated by the vaginal process of the temporal bone, and by attachments of fascia,—and which, from the importance of its contents, deserves careful consideration, is the posterior pharyngeal; it lies closely beneath the base of the skull, (from the vaginal process to the median line) between the pharynx and spine, and includes the carotid, jugular, and condylic canals, and the organs traversing them.

If now an oblique line be carried across the neck, from the sterno-clavicular articulation to the tip of the mastoid process, it divides, as a diagonal, the remaining quadrilateral surface of the neck into two triangles; an anterior one having its apex at the sterno-clavicular joint, and its base along the posterior belly of the digastric muscle; a posterior one, having, its base at the inner two-thirds of the clavicle,—its apex at the mastoid process,—its posterior side formed by the trapezius,—its anterior border defined by the imaginary line which demarks it from the anterior triangle. The omo-hyoid muscle, in its reflected course, crosses both these triangles, subdividing them; and since the angle of its bend falls just on the line of their separation, and since it proceeds from behind the outer third of the clavicle to the body of the hyoid bone, it acts as a second diagonal in the neck, dividing each into an upper and a lower triangular space. These four triangles will be described in detail; and since the sterno-mastoid (which is too substantial to be treated as a mere boundary-line) enters into all of them, and has to parts of each relations of the extremest practical importance, some separate, chiefly recapitulatory, consideration will be given to its relative anatomy. Finally, to ensure for the organs of the median line the consideration they require (the usefulness of which mainly depends on their being