Page:Muscles and Regions of the Neck.djvu/23

Rh approaches the root of the neck than in adult growth, and, as also the branches arising from it, may more easily be endangered in tracheotomy and other operations in the neighbourhood. Its length is somewhat above an inch: its direction obliquely upward and outward, toward the sterno-clavicular joint, opposite to which it divides. In this course it corresponds, behind, to the trachea,—in front to the sternum, from which the remains of the thymus gland, the origin of the sterno-hyoid and sterno-thyroid muscles, and (close to its origin) the transverse crossing of the left vena innominata separate it,—externally, to its accompanying vein, and, mediately, to the pleura,—internally, to the left carotid from which it is separated by a triangular interval in which the thymus, or its remnant, lies upon the trachea.

The frequency of its undue extension beyond the precise limit assigned to it, and consequent appearance in the sub-hyoid region of the neck, together with the fact of its often furnishing a middle inferior thyroid artery, are contingencies never to be disregarded in operations thereabout.

This artery has now been tied for cure of aneurism at least six times; unsuccessfully—it is true—but with such nearness to success as not to forbid cautious repetition. The mode of procedure adopted by Dr. Mott consisted in a transverse division of the skin, muscles, and fasciæ along the edge of the clavicle and sternum,—in raising these, and taking the subclavian and carotid arteries (which he seems to have denuded to some extent) as guides to the innominata, in drawing the jugular vein, the vagus, phrenic and recurrent nerves outwards, in pressing the pleura carefully downwards with the convexity of the needle, while he carried its point from below upwards around the vessel.

6. The digastric space is bounded below by the curve of the digastric muscle, and extends above within the angle and horizontal ramus of the jaw, so that, if considered as a triangle, it may be described as having its base represented by the internal oblique (or myloid) ridge of the lower jaw, and an imaginary prolongation of this to the root of the mastoid process,—its anterior border formed by the ascending belly of the digastric muscle,—its posterior by the descending fibres of the same; and its apex will obviously be at the point of their reflexion by the hyoid bone. The skin, the superficial fascia with the platysma, and the cervical aponeurosis, wall it in, and that part of the inferior maxilla which lies beneath the oblique line, to the basial edge of which the fascia adheres, overhangs it; its deep surface is constituted by the mylo-hyoid muscle and by the side of the tongue and pharynx in front, by the vaginal and styloid processes of the temporal bone behind. A fibrous slip, reflected outwardly from the styloid process to the angle of the jaw, and to the deep surface of the aponeurosis, distinctly divides the digastric space into two parts. Of these, the posterior is the smaller; its vertical extent is to the temporo-maxillary articulation: backwards it is bounded by the auditory canal and mastoid process; inwardly, by the vaginal plate, the styloid process and its muscles. In the anterior direction the border of the jaw, together with the septum just described, are its limits: whence it seems, within the neck of the jaw, to prolong itself as an interspace between the attachments of the pterygoid muscles.

Between the unyielding walls of this narrow space, the parotid gland contracts itself into a wedge-like form, reaches in the one direction to the styloid process and is folded round it, in the other is prolonged with the maxillary vessels between the insertions of the pterygoidei. In its substance the external carotid ascends to its terminal subdivision,—the portio dura curves from the stylo-mastoid foramen, and breaks into the lash of communicating branches, known as pes anserinus,—the roots of the external jugular vein unite to assume that name,—and junctions of the portio dura with the superficial temporal nerve, and with the auricular branch of the cervical plexus, are met with. Its remarkable impaction behind the jaw is probably designed for affecting its function by the mechanical stimulus of the masticatory movements. Its enlargement may inconveniently hinder these motions, and, where accompanied by much induration, actually lock the jaw. The merely anatomical difficulties of extirpating the parotid gland have probably been somewhat over-rated; but cases requiring the operation must be of exceeding rareness. Absorbent glands lie on many points of its surface, and in its substance; their enlargement is frequent, and has been mistaken, in several instances, for an affection of the parotid itself.

The arteries met with in this space are all branches of the external carotid: the occipital and auricular follow its posterior border, the latter usually traversing a part of the gland; the temporal artery emerges at the upper, the transverse facial at the anterior edge of the parotid, while from its deep portion the internal maxillary passes forward, within the neck of the jaw, toward the zygomatic fossa.

The anterior division of the digastric space considerably exceeds the posterior in size: its vertical extent behind is from the curve of the digastric up to the outward surface of the buccal mucous membrane, where reflected from the molar alveoli to the side of the tongue; but anteriorly it seems to be limited by the lower surface of the mylo-hyoid muscle, and so to be shallower; though, in reality, this is not the case, for the muscle referred to merely forms a partial septum, dividing the shallow and superficial part, just mentioned, from a deeper, sublingual portion of great importance. The anterior division of the digastric space may accordingly be considered as bounded above by the mucous membrane of the mouth in its reflexion from the oblique line of the jaw to the border of the tongue, in an extent reaching from the base of the coronoid process to the symphysis; and, internally, by the side of the tongue, (presenting the muscular substance of the genio-hyoideus, genio-hyoglossus, hyoglossus, and stylo-glossus,) and by that of the pharynx. It is only in front that the mylo-hyoid muscle, as