2. Subcutaneous to the integument is a dense and lamellated_ cellular tissue, with little fat, and such as does exist. deposited in small pellets, much more nume rous in the posterior part of the region. This cellular membrane is very intimately connected with those parts of the scalp especially from which hairs grow ; it is much more loose and less adipose in the frontal region ; it also ad heres pretty closely to the subjacent aponeurotic expansion of the occipito-frontalis muscle. The bulbs of the hairs are lodged in it. The firm adhesion of this cellular membrane on the one hand to the skin,- and on the other to the subjacent aponeurosis, is sufficient to ac count for the great pain and danger which at tend punctured wounds of the scalp, in conse quence of the non-extensibility of the membrane and the tension which a very slight degree of swelling consequently gives rise to.
3. the scalp and subcutaneous tissue be divided by a transverse incision over the vertex, and the flaps carefully dissected off, —one as far as the eyebrows, the other to the superior curved line of the occipital bone, the occipito-frontalis muscle is brought into view. _ Anteriorly and inferiorly we find the few fibres of the orbicularis palpebrarum muscle overlap ping the occipito-frontalis just above the mar gin of the orbit.
Occipito7frontalis (epicranius, Albin. : de scribed by some anatomists as two distinct muscles, the ,frontal and occipital).
This is an expanded digastric muscle occu pying the whole of this region. The two bellies of which the muscle is composed are united in the centre by a broad aponeurotic expansion. The anterior belly corresponds to a great part of the frontal bone, and the posterior to a part of the occipital. Very frequently the fibres are weak and pale, so that the dissector finds it difficult to trace out the extent arid attachments of the muscle ; and, moreover, even in its most developed state it is a thin muscle, so that great care is required for the accurate dissection of it.
The anterior belly of this muscle, or that which is by some called the frontal, consists distinctly of two lateral portions united by a. narrow triangular slip of aponeurosis. Each portion is connected inferiorly to the integu ment of the eyebrow through the intervention of cellular membrane, and slightly overlapped by the superior fibres of the orbicular muscle of the eyelids, and commingled with some of. .the fibres of the last named muscle, as well as of the corrugator supercilii. The aponeurotic
slip before alluded to, situated in the middle line, forms the internal boundary of each la teral portion. On the outside the fibres gra dually shorten and extend a very short distance into the temporal region, over the temporal fascia. Each portion presents a convex margin above, which is inserted into the thin tendinous aponeurosis, which extends over the middle portion ofthe occipito-frontal region, correspond ing to the posterior margin of the frontal bone, the fronto-parietal suture, internal portions of the parietal bones, the sagittal and lambdoidal sutures and part of the occipital bones, but se parated from them by the pericranium and by some fine cellular tissue which connected the aponeurosis to the last-named membrane. This aponeurosis is called the cranial or epicranial aponeurosis : in some instances its fibrous cha racter is very distinct in all its extent ; but very frequently it is most manifest in its posterior third or half, the anterior part being little more than condensed cellular membrane, excepting near to the fleshy fibres of the frontal portion of the muscles, where the aponeurotic structure again becomes manifest. On the sides this aponeurosis gradually degenerates into cellular membrane without leaving any defined margin. The aponeurosis in its whole extent adheres closely to the superjacent subcutaneous cellular tissue and to the subjacent pericmnium through the intervention of a fine cellular membrane already referred to. Proceeding from before backwards, we find that this aponeurosis ends in affording insertion. to the fibres which form the posterior belly of the muscle.
This portion of the muscle, also called the Occipital muscle, consists likewise of two lateral portions which are attached inferiorly to the ex ternal part of the superior curved line of the occipital bone, and to the mastoid portion of the temporal. The fibres are parallel and nearly vertical, inclining a little inwards, and are inserted, as already described, into the pos terior margin of the epicranial aponeurosis. The attachment of the muscle to the occipital bone is immediately above that of the sterno mastoid and splenins muscles. On the sides the fibres gradually disappear over the mastoid portion of the temporal bone, and the fleshy belly of the inuscle lies immediately over the pericranium, some cellular membrane only in tervening; its adhesion to the skin, however, is less intimate than that of the frontal portion.