CRANIUM, REGIONS AND MUSCLES OF THE, (Surgical Anatomy.)—If a line be drawn on the skull from the external ancrular process of the frontal bone, backwards :long the rough line on that and the parietal bone, which indicates the attachment of the temporal fascia, be continued downwards and backwards parallel and a little external to the occipito mastoid suture, and then be carried forwards along the inferior surface of the occipital bone to end just behind the foramen jugale, and a little internal to the stylo-mastoid foramen,—this line, with another similar one on the other side, will include an oblong region which has very natural limits both before and behind. Ante riorly this region is limited on each side by the anterior margins of the roof of the orbit, in the centre by the line of articulation of the frontal bone with the nasal and superior maxil lary, posteriorly by the superior curved line of the occipital bone, and on each side by the mastoid process. To this oblong region may be appropriately given the designation occipito frontal region.
The line which thus limits laterally the region just named circumscribes another region which occupies nearly the whole lateral surface of the cranium, and which is called the temporo parietal region. This region passes into the base of the cranium, and may be limited below and within by a line from the styloid process external to the glenoid cavity, as far as the spheno-maxillary fissure.* Occipito-frontalregion.—The anterior and posterior boundaries of this region are suffi ciently obvious on the integuments, the eye brows forming the anterior, the posterior being constituted by a line extending as far as the mastoid process on each side of the occipital protuberance corresponding to the insertion of the superficial muscles of the back of the neck, which protuberance can be felt through the integuments. The lateral limits, however, are not so distinct; in the living subject, however, when the temporal muscle is rendered tense, a distinct line of demarcation is felt along the upper margin of this muscle, extending down wards and backwards nearly as far as the mas toid process.
We proceed to examine the several structures which are presented to the anatomist as he pursues the dissection of this region.
1. is in this region that we can best examine the general characters of the integument of the cranium, commonly known under the name of scalp (Fr. cuir chevelu). The greatest part of it is remarkable for the more or less luxuriant growth of hair from the nature of which, it is hardly necessary to observe, differs materially in the male and in the female. In the natural state about two thirds or three-fourths of the scalp are covered with hair, the anterior third or fourth,—namely, the skin of the forehead,—being uncovered. In front the hairs terminate abruptly on the frontal region ; behind they terminate less ab ruptly, and descend in general to a variable distance on the posterior part of the neck, becoming finer and more downlike as they descend. The natural direction of the hairs is at right angles with that portion of the scalp flom which they grow; consequently the dif ference of direction of the hairs depends upon the differences in the aspects of those regions. This is most obvious in that part of the head which is'called the crown, which in most per sons inclines downwards and backwards to a greater or less extent. Such, however, is the influence of art in the arrangement of the hair, that it is difficult to meet with " a head of hair"—to borrow the phrase from the hair dresser,—where the growth is perfectly na tural.
There is an obvious difference in the nature of that portion of the scalp from which hairs grow, and that which is naturally bald : the former is much thicker and denser, owing, no doubt, to a larger developement of the fibres of the corion, and to the great magnitude of the hairs which pierce it. It is at the posterior part of the occipito-frontal region that the hairs are strongest, and that portion of the scalp very rarely becomes bald.