Page:Muscles and Regions of the Neck.djvu/10

8 constitutes, in lean subjects, a manifest and resisting lamina, yet, in those of an opposite character, it is rendered indistinct by the predominant adipose tissue which occupies its areolæ. Along the side of the neck, from the clavicle to the jaw, these layers are kept asunder by the platysma myoides, which adds, as it were, a third lamina to the subcutaneous expansion; but both in front and behind, where the muscle ceases, they are in close relation, and constitute a single covering to those regions of the neck. The deep layer of this fascia is traversed by the cutaneous nerves and vessels, including the external jugular vein.

2. The cervical fascia is a proper aponeurotic investment of this region, and corresponds in its general characters to the fibrous sheathings of the limbs. Like these, it not only forms a general, compressive, and modelling cincture for the part, but, by various secondary splittings, furnishes dissepiments which isolate the different organs, and allot to each its proper sheath or fascial chamber. It may be briefly, but insufficiently, described as originating from a kind of linea alba, or mesial commissure in front, and in its backward course to the spinous processes furnishing a separate investment to every organ which it encounters, and attaching itself, both below and above, to the chief bony eminences which present themselves. (A section of it, as it thus cellulates the neck, is represented, with Bourgery’s almost invariable accuracy, in a lithograph, (vol. vi. pl. 10,) from which the accompanying woodcut is copied.) It requires, in at least many regions of the neck, a more particular description than this summary contains; and I shall accordingly proceed to consider such portions of it with some detail. The sterno-cleido-mastoideus is ensheathed through its whole extent; the fascia, on reaching its anterior edge, is bi-laminated, encloses the muscle, and becomes again single at its posterior border. When this sheath is laid open by removing its anterior wall, and the muscle carefully everted from its prismatic cell, it will be seen that the posterior lamina is of greater strength than the removed anterior one; and this surface is the one from which the dissector may most conveniently trace the further spread of the membrane. He will find that the cervical fascia (of which the portion covering the sterno-cleido-mastoideus is but a secondary slip) extends itself from behind that muscle in all directions; inwardly to the mesial line,—outwardly to the trapezius,—upwardly to the jaw,—downwardly to the clavicle. a. Traced inwardly, its arrangement differs in the upper and lower parts of the neck; 1. in that below the os hyoides a superficial lamina covers the subhyoid muscles, joins its fellow in the median line, and is fixed below to the interclavicular notch of the sternum; a second, thin process divides the sterno-thyroid from the sterno-hyoid muscle; a third, stronger one, passing between the sterno-thyroid and air-tube, covers this latter organ and the thyroid body, is attached below to the inner surface of the manubrium sterni, internally joins the layer from the opposite side, and helps with it to form a raphe, reaching from the os hyoides to the sternal notch. Previously to the divisions here mentioned, the fascia encloses the flat tendon and anterior belly of the omo-hyoid muscle; and in a line, which will presently be more particularly indicated, covers the carotid artery, jugular vein, and nervus vagus. Just external to these parts, along the outer edge of the jugular vein, it detaches a delicate process, which passes behind the vessels, separating them from the sympathetic nerve, and is continued inwardly to join its fellow from the opposite side, as a cellular clothing to the œsophagus. 2. Above the os hyoides, the arrangement of the fascia is simpler; covering the mylo-hyoid and submaxillary gland, and inclosing the anterior belly of the digastric, it is fixed to the lower border of the symphysis, and hence to a mesial raphe as far as the os hyoides. It has some deep connexions, to which I shall return directly; and, to the sheath of the great cervical vessels it preserves the same relations as below, its deepest process losing itself on the pharynx. b. Traced upwardly, the fascia is seen to split on the inferior edge of the digastric muscle; the superficial lamina is attached, behind, to the mastoid process,—in front, joining the part last described, to the lower edge of the jaw,—and, intermediately, ascends upon the parotid gland, which it invests; the deeper layer is fixed to the styloid process of the temporal bone, and gives origin to a remarkable septal slip, (sometimes called the stylo-maxillary ligament,) which, just in front of the posterior belly of the digastric, passes outwardly, is inserted into the deep surface of the superficial lamina and into the angle of the jaw, so serving to separate the space, circumscribed by the digastric muscle, into two parts, and isolating the parotid gland, which occupies the posterior of these, from the submaxillary, which is situated in the anterior one. Further, this deep layer (joined by a slip from the fascia, which covers the submaxillary gland and is attached to the jaw) prolongs itself around Wharton’s duct, between the mylo-hyoid and hyo-glossal muscles, and likewise furnishes origin to the investing cellular tissue of the pharynx. c. Below, the cervical fascia attaches itself around the insertions of the muscles, which it incloses, viz. towards the median line to the notch of the sternum, and—with the sub-hyoid muscles—to the deep surface of the manubrium and to the cartilage of the first rib, and then to the clavicle in its entire length, both around and between the sterno-cleido-mastoid and trapezius. In descending to the clavicle, it ensheathes the posterior belly of the omo-hyoid; and a firm process of it, folded around this muscle and directed backward to the levator anguli scapulæ, is infixed along the superior costa of that bone, and circumscribes the so-called omo-hyoid space. d. Traced outwardly and backwardly the fascia covers in the interval between the trapezius and sterno-masioid (posterior triangle) from the clavicle to the occiput, and, on arriving at the anterior edge of the trapezius, splits to enclose it. The further distribution of it, in this direction, is in