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14 Commentary on plates 3 & 4.

The posterior cervical triangle, 9, 8, 7, Plate 4, in which the subclavian artery is situated, is again sub­divided by the muscle omo-hyoid into two lesser regions, each of which assumes somewhat of a trian­gular shape. The lower one of these embraces the vessel, A, and those nerves of the brachial plexus, I, which are in contact with it. The posterior belly of the omo-hyoid muscle, K, and the anterior scalenus muscle, N, form the sides and apex of this lesser tri­angular space, while the horizontal clavicle forms its base. This region of the subclavian artery is well defined in the necks of most subjects, especially when the muscles are put in action. In lean but muscular bodies, it is possible to feel the projection of the ante­rior scalenus muscle under the skin, external to the sterno-mastoid. The form of the omo-hyoid is also to be distinguished in the like bodies. But in all subjects may be readily recognised that hollow which occurs above the clavicle, and between the trapezius, 8, and the sterno cleido-mastoid, 7 B, in the centre of which hollow the artery lies.

The contents of the larger posterior cervical tri­angle, formed by B, the sterno-mastoid before; 9, the splenius; and 8, the trapezius behind, and by the clavicle below, are the following mentioned structures--viz., A, the subclavian artery, in the third part of its course, as it emerges from behind N, the scalenus anticus; L, the transversalis colli artery, a branch of the thyroid axis, which will be found to cross the subclavian vessel at this region; I, the brachial plexus of nerves, which lie external to and above the vessel; H, the external jugular vein, which sometimes, in conjunction with a plexus of veins coming from behind the trapezius muscle, entirely conceals the artery; M, the posterior scapular artery, a branch of the subclavian, given off from the vessel after it has passed from behind the scalenus muscle; O, numerous lymphatic glands; P, superficial descending branches of the cervical plexus of nerves; and Q, ascending superficial branches of the same plexus. All these structures, except some of the lymphatic glands, are concealed by the platysma myoides A, as seen in Plate 3, and beneath this by the cervical fascia, which latter shall be hereafter more clearly represented.

In somewhat the same mode as the posterior half of the omo-hyoid subdivides the larger posterior triangle into two of lesser dimensions, the anterior half of the same muscle divides the anterior triangle into two of smaller capacity.

The great anterior triangle, which is marked as that space inclosed within the points, 6, the top of the sternum, the mental symphysis and the angle of the maxilla; and whose sides are marked by the median line of the neck before, the sterno-mastoid behind, and the ramus of the jaw above, contains C, the common carotid artery, becoming superficial from beneath the sterno-mastoid muscle, and dividing into E, the internal carotid, and D, the external carotid. The anterior jugular vein, 3, also occupies this region below; while some venous branches, which join the external and internal jugular veins, traverse it in all directions, and present obstacles to the operator from their meshy plexiform arrangement yielding, when divided, a profuse haemorrhage.

The precise locality at which the common carotid appears from under the sterno-mastoid muscle is, in almost all instances, opposite to the thyroid cartilage. At this place, if an incision, dividing the skin, pla­tysma and some superficial branches of nerves, be made along the anterior border of the sterno-mastoid muscle, and this latter be turned a little aside, a pro­cess of cervical fascia, and beneath it the sheath of the carotid artery, will successionally disclose them­selves. In many bodies, however, some degree of careful search requires to be made prior to the full exposure of the vessel in its sheath, in consequence of a considerable quantity of adipose tissue, some lymphatic glands, and many small veins lying in the immediate vicinity of the carotid artery and internal jugular vein. This latter vessel, though usually lying completely concealed by the sterno-mastoid muscle, is frequently to be seen projecting from under its fore part. In emaciated bodies, where the sterno-mastoid presents wasted proportions, it will, in consequence, leave both the main blood-vessels uncovered at this locality in the neck.

COMMENTARY ON PLATES 3 & 4. 15

The common carotid artery ascends the cervical region almost perpendicularly from opposite the sterno-clavicular articulation to the greater cornu of the os hyoides. For the greater part of this extent it is covered by the sterno-mastoid muscle; but as this latter takes an oblique course backwards to its insertion into the mastoid process, while the main blood-vessel dividing into branches still ascends in its original direction, so is it that the artery becomes un­covered by the muscle. Even the root of the internal carotid, E, may be readily reached at this place, where it lies on the same plane as the external carotid, but concealed in great part by the internal jugular vein. It would be possible, while relaxing the sterno­-mastoid muscle, to compress either the common caro­tid artery or its main branches against the cervical vertebral column, if pressure were made in a direction backwards and inwards. The facial artery V, which springs from the external carotid, D, may be com­pressed against the horizontal ramus of the lower jaw-bone at the anterior border of the masseter muscle. The temporal artery, as it ascends over the root of the zygoma, may be compressed effectually against this bony point.

The external jugular vein, H, Plate 4, as it descends the neck from the angle of the jaw obliquely back­wards over the sterno-mastoid muscle, may be easily compressed and opened in any part of its course. This vein courses downwards upon the neck in rela­tion to that branch of the superficial cervical plexus, named auricularis magnus nerve, Q, Plate 4, G, Plate 3. The nerve is generally situated behind the vein, to which it lies sometimes in close proximity, and is liable, therefore, to be accidentally injured in the per­formance of phlebotomy upon the external jugular vein. The coats of the external jugular vein, E, Plate 3, are said to hold connexion with some of the fibres of the platysma-myoides muscle, A A, Plate 3, and that therefore, if the vessel be divided transversely, the two orifices will remain patent for a time.

The position of the carotid artery protects the vessel, in some degree, against the suicidal act, as generally attempted. The depth of the incision necessary to reach the main blood-vessels from the fore part of the neck is so considerable that the wound seldom effects more than the opening of some part of the larynx. The ossified condition of the thyroid and cricoid parts of the laryngeal apparatus affords a protection to the vessels. The more oblique the inci­sion happens to be, the greater probability is there that the wound is comparatively superficial, owing to the circumstance of the instrument having encoun­tered one or more parts of the hyo-laryngeal range; but woeful chance sometimes directs the weapon horizontally through that membranous interval be­tween the thyroid and hyoid pieces, in which case, as also in that where the laryngeal pieces persist perma­nently cartilaginous, the resistance to the cutting instrument is much less.

The anatomical position of the parotid, H, Plate 3, and submaxillary glands, W, Plate 4, is so important, that their extirpation, while in a state of disease, will almost unavoidably concern other principal structures. Whether the diseased parotid gland itself or a lym­phatic body lying in connexion with it, be the subject of operation, it seldom happens that the temporo­-maxillary branch of the external carotid, F, escapes the knife. But an accident, much more liable to occur, and one which produces a great inconvenience afterwards to the subject, is that of dividing the portio-dura nerve, S, Plate 4, at its exit from the stylo-mastoid foramen, the consequence being that almost all the muscles of facial expression become paralyzed. The masseter, L, Plate 3, pterygoid, buccinator, 15, Plate 4, and the facial fibres of the pla­tysma muscles, A O, Plate 3, still, however, preserve their power, as these structures are innervated from a different source. The orbicularis oculi muscle, which is principally supplied by the portio-dura nerve, is paralyzed, though it still retains a partial power of contraction, owing to the anatomical fact that some terminal twigs of the third or motor pair of nerves of the orbit branch into this muscle.

The facial artery, V, and the facial vein, U, Plate 4, are in close connexion with the submaxillary gland. Oftentimes they traverse the substance of it. The lingual nerve and artery lie in some part of their course immediately beneath the gland. The former two are generally divided when the gland is excised; the latter two are liable to be wounded in the same operation.

DESCRIPTION OF PLATES 3 & 4.

PLATE 3.

A A A. Subcutaneous platysma myoides muscle, lying on the face, neck, and upper part of chest, and covering the structures contained in the two surgical triangles of the neck.

B. Lip of the thyroid cartilage.

C. Clavicular attachment of the trapezius muscle.

D. Some lymphatic bodies of the post triangle.

E. External jugular vein.

F. Occipital artery, close to which are seen some branches of the occipitalis minor nerve of the cervical plexus.

G. Auricularis magnus nerve of the superficial cervical plexus.

H. Parotid gland.