Between the unyielding walls of this nar row 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 max illary vessels between the insertions of the pterygoidei. In its substance the external ca rotid ascends to its terminal subdivision,—the portio dura curves from the stylo-rnastoid fora men, 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 durawith the superficial temporal nerve, and with the auri cular branch of the cervical plexus, are met with. Its remarkable impaction behind the jaw is probably designed for affecting its func tion by the mechanical stimulus of the masti catory movements. Its enlargement may in conveniently 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 sur face, 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 pa rotid, 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 digastrie space cOnsiderably exceeds the posterior in size : its vertical extent behind is from the curve of the dig,astric up to the outward surface of the buccal mucous membrane, where reflected from the molar alveoli to the side of the tong-ue ; but an teriorly it seems to be limited by the lower sur face 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 paitial septum, dividing the shallow and super ficial part, just mentioned, from a deeper, sub lingual portion of great importance. The ante rior division of the digastric space may accord ingly 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 syrnphysis ; 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 a partial septum, divides a superficial space front the general submucous tract ; and it is necessary to understand this arrangement, in order to apprehend the mode in which the sub maxillary gland approaches the mucous mem brane of the mouth : the gland lies in the su perficial division of the space, and it is round the posterior edge of the mylo-hyoid muscle that its duct is reflected in proceeding to dis charge itself, which by so entering the sublin gual space it is enabled to do. The anterior division of the diga.stric space contains, super 5cially the gland just mentioned, the facial artery and vein with some of their branches, the mylo-hyoid twig from the third division of the fifth, and many lymphatic ganglia. The gland receives a thin capsular investment from the deep surface of the fascia, closing the space, and this prolongation contracts and condenses itself round the posterior extremity and duct, accompanying these in their turn round the mylo-hyoid, and furnishing the duct with a dense fibrous tunic. The artery enters the space from below, by passing beneath the pos terior belly of the digastric muscle, very tor tuously winds through the submaxillary gland, and bends over the basial edge of the jaw a little in front of the masseter. It furnishes a deep ascending branch (the tonsillary) near the angle of the jaw and many glandular twigs; but its only considerable branch in this region is the sub-mental, which runs toward the me dian line jtist beneath the jaw, and, supplying the mylo-hyoid muscle on which it is applied, and the anterior belly of the digastric. termi nates by freely communicating with its fellow. The sub-mental branch derives additional im portance from the frequency of an anomalous distribution, by vvhich, piercing the mylo-hyoid muscle and entering the sublingual space, it partly discharges the functions of the lingual artery in supplying the sublingual gland. The facial vein lies behind the artery, and quits the space below in passing over the digastrie and stylo-hyoid muscles, which divide it from the artery. Its usual or chief termination is in the internal jugular ; hut it frequently contributes more or less to form the external or the ante rior jugular vein. The mylo-hyoid nerve runs parallel to the origin of the muscle, which gives it its name, and supplies it and the anterior belly of the dig,astric. The lymphatic glands are numerous and important: they receive the absorbent vessels from the face and likewise from the mouth and pharynx, are the frequent seat of stnimous inflammation, readily sympa thize in disnrdered conditions of the fauces and alveoli, and take an active part in propagating the malignant influence of cancerous ulcerations on the face. These parts are all covered in by the aponeurosis,—which fixes itself to the base of the jaw,—and by the platysma and superficial fascia,—which continue themselves on the face. They are readily accessible to the surgeon, but seldom subjected to any operation of impor tance. The deep or sublingual portion of the digastric space has its roof formed by the mu cous membrane, which, between the tongue and alveolar arch, constitutes the floor of the mouth : the side of the tongue and the continuous sur face of the pharynx, as already described, com pose its inner wall ; and it follows from the previous description that, in part at least, the mylo-hyoid is its floor. The gustatory nerve runs through it beneath the mucous membrane, which it supplies: the hypo-glossal, describing a parallel but inferior curve, is distributed in succession to the muscles of the inner wall of the space ; the glosso-pharyngeal between these two in heig,ht, but confined to the root of the tongue, bends inwardly beneath the stylo glossus ; the lingual artery, emerging from under cover of the hyo-glossus, which has hidden its tortuous ascent, divides anteriorly into two branches ; a ranine, which follows the curved border of the tongue to its tip, where it archingly unites with its fellow ; a sublingual, which directing itself a little outward, supplies the third salivary gland : this little body lies on the divergent fibres of the genio-glossus, near their origin, and close beneath the membrane of the mouth : finally, the duct of the submaxillary gland, traversing the space obliquely, crosses its.
contents, and communicates with the cavity of the mouth just beside the frcenum. This space is the seat of ranula (a tumour formed by ob struction of the submaxillary duct), and of) some salivary concretions ; in both which com-I plaints the distended canal is brought so imme diately beneath the mucous membrane, which it raises, that other parts are little liable to in jury : here, too, it is that the surgeon, when. obliged to divide the frcenum lingute, must: cautiously cut the too tight fold near to the' symphysis, and vertically, lest, in extending" his incision backward, he should wound the ranine artery. Sharp instruments penetrating downward be.side the tongue may wound the sublingual artery, and the consequent hmor rhage, distending the submucous space, raise the reflected membrane on each side into swell ings of such size, as to suggest imminent peril of suffocation." 7. The small region to which, under the name of posterior pluoyngeol, I propose giving brief notice, has for its roof the basilar portion of the occiput and petrous part of the temporal bone, and presents in this direction the orifices of the jugular, carotid, and anterior condylic canals : it extends downwards between the pha rynx and vertebrx into the anterior triangle of the neck, and is separated from the posterior division of the digastric space, within which it lies, by the styloid and vaginal processes, and by the attachment to these of a strong layer of fascia, which passes beneath the dig,astric mus cle. The internal carotid artery, surrounded by branches from the superior cervical ganglion, ascends here ; and since, from the angle of the jaw to the base of the skull, it lies beside the pharynx, covered by the lateral parts of that cylinder, it is liable to be involved in a punc tured wound from the mouth; and this unfor tunate accident has not unfrequently occurred in operations on the tonsil, which organ in its swollen state is so closely applied to the in ternal carotid artery, that if it were transfixed by a bistoury in an outvvard direction, the vessel could hardly escape. Hence the im portance of care, in relieving tonsillary ab scesses, to direct the point of the instrument, as much as possible, towards the median line, a,nd to select for incision that part of the cyst which most nearly adjoins the palate. The jugular vein emerges behind the artery and runs downwardly along its outer side : of the three divisions of the eighth nerve, which leave the cranium in front of the vein, the glosso pharyngeal is applied to the outer, the vagus and spinal accessary to the inner part of its circumference. The muscular branch of the latter winds from within behind the vein, and obliquely descends to the sterno-mastoid : the vagus continues to descend vertically along its inner side, but both the glosso-pharyngeal and hypo-glossal nerves obliquely cross between it and the artery, and subsequently arch over the latter in their passage to the tongue. From its relations to the vertebra in this space, the pha lynx may participate in their diseased condi tions, and give vent to abscesses, dependent on caries of the cervical spine. The surgeon may sometimes assist his diagnosis of complaints so situated, by introducing his finger into the pharynx.* 8. Lastly, I proceed to recapitulate, briefly and in connexion, the practical relations of the sterno-cleido-mastoideus in regard of the spaces which have been described. Its clavicular origin is in the inferior division of the posterior triangle, covers the subclavian artery in the first and second portions of its course, and in many instances extends this origin so far outwardly as to hide the vessel during a considerable part of its third stage ; it likewise, of course, covers many parts lying between it and the artery,— the jugular and subclavian veins, the vagus and phrenic nerves, the scalenus anticus and omo hyoid muscles, and the origin and divergence of many arterial branches: these fibres obviously require division, varying according to circum stances, vvhen the subclavian artery is to be exposed. The interval between its origins cor responds to the sterno-clavicular joint, and, on the right side, to the bifurcation of the arteria innominata : along the cellular line, prolonged from this interval, (which answers to the dia gonal dividing the two great triangles,) M. Se dillot proposes to penetrate, without section of muscular fibre, in order to reach tFe common carotid artery. The sternal head of k.e niuscle, directing itself backward, obliquely crosses, in the inferior segment of the great anterior trian gle, the sheath of the vessels, from which the sub-hyoid muscles partly divide it. In order to reach the conimon carotid artery these fibres are accordingly cut asunder, except where the operator prefers the anatomicalfinesse of M. Se dillot's plan. Tracing the muscle in the middle of the neck, we find it a most serviceable guide in operations on tbe common carotid, and on its primary or secondary branches. A vertical incision directed to the point of its intersection with the omo-hyoid muscle (nearly opposite the cricoid cartilage) enables the surgeon conve niently to draw these muscles aside, and to expose, according as the wound is higher or lower, the external and internal carotids, or the trunk from which they orioinate, and, in close connexion with the anteriorlayer of their sheath, the descending branch of the hypo-glossal. Finally, about and above the level of the hyoid bone, the anterior edge of the sterno-mastoid, with the posterior belly of the digastric, and the cornu of the os hyoides, furnish definite marks for discovering the superior thyroid, the lingual, the facial or the continued external carotid artery; since, in the space so bounded, the last named vessel vertically ascends, the first alinost horizontally advances, and the other two pass to their destinations with intermediate obliqu ity.