This muscle is evidently destined to act upon the integuments of the cranium : its influence is most apparent upon the skin of the forehead and eyebrows ; it distinctly raises the latter, and throws the former into transverse wrinkles. Under its influence the whole scalp may be made to move backwards and forwards, but the occipital portion of the muscle cannot create, as the frontal does, wrinkles in its corresponding integument, owing to the less firm adhesion of the muscle to it.
Subjacent to the anterior portion of the occi pito-frontalis is the carragator supercilii muscle. It lies on the inner half or third of the orbital margin of the frontal bone. By its inner extre mity it is attached to the internal angular pro cess of the frontal bone; the fibres pass thence outwards, inclining a little upwards, and are inserted into the integument of the eyebrow, being mixed with the orbicularis and occipito frontalis muscle. This muscle evidently can depress the eyebrow, and acting in conjunction with its fellow, throw the integuments -into vertical wrinkles, approximating the eyebrows, and occasioning the act of frowning. This muscle lies on the supra-orbital nerve and vessels.
4. Nerves.—The anterior part of the occi pito-frontal region is freely supplied with nerves from those branches of the ophthalmic portion of the fifth which originate within the orbit. Of these the supra-orbital is the largest : imme diately after its emergence from the supra-or bital foramen this nerve divides into a series of branches which pass up on the forehead, some adhering to the pericranium, others distributed to the muscle, and others becoming subcu taneous. IIere, too, we find ramifications of the supra-trochleator or internal frontal nerve, chiefly distributed in the internal portion of the muscle. At the external part of this frontal region we find some filaments of the portio dura. In the posterior or occipital region the principal nerves are derived from the cervical plexus; tbe auricular and mastoid branches of this plexus distribute their filaments here; and we also find ramifications from the posterior branch of the first cervical nerve, accompany ing the subdivisions of the occipital artery.
5. Arteries.--In front we have ramifications of the supra-orbital and superficial temporal freely anastomosing with each other; and deeper-seated, a few branches of the deep temporal, distributed to the pericranium. In
the occipital region we have the occipital, often of considerable size, and the posterior auricular also sends some of its ramifications to anastomose with the occipital branches. Both in front and behind, the arteries of oppo site sides inosculate with each other on the middle line.
6. Veins.—Small veins accompany most of the arteries ; but the most remarkable vein is one which is situated in the frontal region nearly on the middle line ; it is the frontal vein, or vena preparata, sometimes replaced by two or three. Velpeau advocates the re vival of the ancient practice of bleeding from this vein in head affections. It carries the blood, as he observes, from all the anterior part of the head to the root of the nose, whence he argues that venesection practised on this vessel would empty the whole of the scalp. How often in practice do we see manifest advantage from cupping the temples or some region of the scalp, when little or no benefit had been derived from other modes of practising the detraction of blood ! 7. Lymphatics.—The lymphatics are very few, and pass into the parotid ganglions, or those behind the ear or in the superior part of the neck.
8. Pericranium .—This fibrous tissue, pos sessing the same properties as the periosteum in other parts of the body, is, in a practical point of view, not the least interesting structure which is to be found in this region. It is largely supplied with blood, more especially in early life. We have already noticed its adhesion to the superjacent aponeurosis ; it adheres to the bone by cellular membrane, and is easily raised from it by dissection in all points except where there are sutures. This membrane is not unfrequently the seat of peri ostitis and of nodes.
II. lateral boundary of the occipito-frontal region consti tutes the superior limit of this region, and a line drawn from the external angular process of the os frontis backwards and a little down wards along the zygoma to the mastoid process of the temporal bone, limits it inferiorly.