Thus, (I) a region of the median line, (2) an antero-iriferior, (3) an antero-superior, (4) a postero-superior, and (5) a postero-inferior tri angle, (6) a &gastric, and (7) a posterior pha ryngeal space, are to be severally considered ; and a few preliminary remarks may be given to the tegurnentary parts, which are more or less common to all.
The skin is fine, thin, and extensible, espe cially below and in front ; becoming coarser and more adherent toward the upper part of the posterior triangle ; it frequently presents some transverse wrinkling above the hyoid bone, which seems to depend on the platysina myoides ; here, too, the follicles are larger and more abundant than in the other parts of the neck, and, in the male subject, the surface is overgrown by the beard. The subcutaneous cellular tissue has already been described ; in the upper part of the posterior triangle it be comes almost inseparably confounded with the cervical aponeurosis ; the platysma myoides lies between its layers and keeps them apart over the greater surface of the neck ; the fibres of this muscle are absent in the lower part of the anterior, and upper part of the posterior triangle, and at these spots the two layers of the superficial fascia fall together and are nearly confounded. In .the deeper lamina of this texture, subjacent to the platysma in the parts where it lies, run the superficial veins and nerves. The external jugular vein commences in the parotid gland, usually by radicles, which correspond to the terminal branches of the ex ternal carotid artery, temporal, internal maxil lary, and transverse facial ; pierces the fascia near the angle of the jaw, and directs itself al most vertically toward the middle of the cla vicle, in the deep layer of' superficial fascia : just at the edge of the clavicular insertion of the sterno-mastoid muscle it bends inward, pierces the aponeurosis, and dischaiges itself into the subclavian vein. It thus very ob liquely crosses the sterno-cleido-mastoideus from its anterior to its posterior edge, sepa rated from that muscle by its fascial sheath ; the auricular nerve runs upward parallel to its posterior border ; the platysma covers it in its whole course with fibres which cross its direction ; its place of discharge into the subclavian vein is usually just opposite the scalenus anticus, covered by fascia and by the sterno-rnastoid muscle. It receives superficial
occipital, superior and posterior scapular veins ; branches from the posterior triangle of the neck, and from the trapezius; it has uncertain and irregular communication with the anterior jugular vein, and receives a certain, though not regular, branch from the internal jugular ; this is usually given to it at the lower part of the parotid, or on its emergence from that gland, and occasionally seems to constitute its com mencement. Obvious surgical inferences from the anatomy of this vein are : the relief that its communication with the internal jugular en ables it to give, when opened in cases of cere bral congestion; the elig,ibility of its ltne of passage over the thick helly of the stemo mastoid for that mode of venesection ; the ne cessity for dividing some fibres yf the platysma transversely to their length (by an lacision nearly in the direction of the sterno-mastoid) in order to obtain a clear opening and free jet of blood ; the need for care in this operation, but still more in proportion as the vein is wounded lower in the neck, to hinder the possibility of air being inspired through its cavity.
The anteriorjugular vein is an irregular sub cutaneous supplement to the external : it com mences in the submental region, near the hyoid bone; descends vertically beside the median line, receiving branches from the larynx, and sometimes from the thyroid body ; on arriving at the sternum, or near that bone, it bends horizontally outward, piercing the fascia, and runs behind the origin of the sterno-mastoid, to throw itself into the suhelavian vein, somewhat within the termination of the external jugular. It generally has free communications with its fellow and with the internal and external ju gular. Its size is in inverse proportion to that of the external ; and, in absence of this, it is generally a very considerable branch ; it is sometanes single and mesial ; but more usually two exist, which are commonly of unequal calibre.