Muscles of the Head

Occipitofrontalis (Epicranius)

The superficial fascia in the scalp is a firm, fibro-fatty layer, intimately adherent to the skin, and to the Occipitofrontalis and its aponeurosis; behind, it is continuous with the superficial fascia at the back of the neck; laterally, it is prolonged into the temporal region, where it is looser in texture.

The Occipitofrontalis (Epicranius) is a broad, musculofibrous layer which covers the top of the skull, from the nuchal lines to the eyebrows. It consists of four bellies–two occipital and two frontal-connected by an intervening aponeurosis, termed the epicranial aponeurosis (galea aponeurotica).

Each Occipital belly, thin and quadrilateral in form, arises by tendinous fibers from the lateral two-thirds of the highest nuchal line of the occipital bone, and from the mastoid part of the temporal bone. It ends in the epicranial aponeurosis.

Each Frontal belly (fig. 579) is thin, of a quadrilateral form, and intimately adherent to the superficial fascia. It is broader than the Occipital belly and its fibers are longer and paler in color. It has no bony attachments. Its medial fibers are continuous with those of the Procerus; its intermediate fibers blend with the Corrugator and Orbicularis oculi; and its lateral fibers are also blended with the latter muscle over the zygomatic process of the frontal bone. From these attachments the fibers are directed upwards, and join the epicranial aponeurosis in front of the coronal suture. The medial margins of the Frontal bellies are joined together for some distance above the root of the nose; but between the Occipital bellies there is a considerable, though variable, interval, occupied by an extension of the epicranial aponeurosis.

The epicranial aponeurosis (galea aponeurotica) covers the upper part of the cranium; behind, it is attached, in the interval between the Occipital bellies, to the external occipital protuberance and highest nuchal line of the occipital bone; in front, it sends a short and narrow prolongation between the Frontal bellies. On each side it gives origin to the Auriculares anterior et superior; in this situation it becomes thinner, and is continued over the temporal fascia to the zygomatic arch. It is closely united to the skin by the firm, fibrofatty superficial fascia; it is connected to the pericranium by loose cellular tissue which allows of the movement of the epicranial aponeurosis, the latter carrying with it the skin of the scalp.

Nerve-supply.–The Occipital belly is supplied by the posterior auricular branch, and the Frontal belly by the temporal branches, of the facial nerve.

Actions.-The Occipital bellies draw the scalp backwards; the Frontal bellies acting from above raise the eyebrows and the skin over the root of the nose; acting from below they draw the scalp forwards, throwing the integument of the forehead into transverse wrinkles. The Occipital and Frontal bellies; acting alternately; move the entire scalp backwards and forwards. In the ordinary action of the Frontal bellies the eyebrows are elevated, thus giving to the face the expression of surprise; if the action be exaggerated, the eyebrows are still further raised, and the slain of the forehead thrown into transverse wrinkles, as in the expression of fright or horror.

Figure 579
Muscles of the face and neck lateral view - Figure 579
A thin muscular slip, termed the Transversus nuchce, is present in about 25 per cent. of cases; it arises from the external occipital protuberance or from the superior nuchal line, either superficial or deep to the Trapezius; it is frequently inserted with the Auricularis posterior, but may join the posterior edge of the Sternocleidomastoid.

Applied Anatomy.-The scalp consists of five layers, viz. the skin, subcutaneous tissue, Occipitofrontalia and its aponeurosis, subaponeurotic areolar tissue, and pericranium (fig. 580). But from a surgical standpoint it is better to regard the first three of these as a single layer, since they are all intimately united, and when torn off in an accident, or turned down as a flap in a surgical operation, remain firmly connected to each other. In consequence of the dense character of the subcutaneous tissue, the amount of swelling which occurs as the result of inflammation is slight; and a wound which does not involve the Occipitofrontalis or its aponeurosis does not gape. The blood-vessels which lie in this tissue do not contract when wounded, and therefore the hemorrhage from scalp wounds is often very considerable. It can, however, always be arrested by pressure -a matter of great importance, as it is often very difficult or impossible to pick up with forceps a wounded vessel in the scalp owing to the retraction of its cut ends.

Figure 580
Scalp and skull, dura mater, arachnoid, and pia mater, coronal section - Figure 580
The subaponeurotic areolar tissue is, from a, surgical point of view, of considerable importance. It is loose and lax, and is easily torn through; and hence, in wounds of the scalp, it is this tissue which is torn when the flap is separated from the parts beneath. The vessels are contained in the flap, and there is little risk of sloughing, unless the vitality of the part has been actually destroyed by the injury.

 


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